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Reason

Reason is the capacity of applying logic consciously by drawing conclusions from new or existing information, with the aim of seeking the truth. It is associated with such characteristically human activities as philosophy, religion, science, language, mathematics, and art, and is normally considered to be a distinguishing ability possessed by humans. Reason is sometimes referred to as rationality.

Reasoning involves using more-or-less rational processes of thinking and cognition to extrapolate from one's existing knowledge to generate new knowledge, and involves the use of one's intellect. The field of logic studies the ways in which humans can use formal reasoning to produce logically valid arguments and true conclusions. Reasoning may be subdivided into forms of logical reasoning, such as deductive reasoning, inductive reasoning, and abductive reasoning.

Aristotle drew a distinction between logical discursive reasoning (reason proper), and intuitive reasoning, in which the reasoning process through intuition—however valid—may tend toward the personal and the subjectively opaque. In some social and political settings logical and intuitive modes of reasoning may clash, while in other contexts intuition and formal reason are seen as complementary rather than adversarial. For example, in mathematics, intuition is often necessary for the creative processes involved with arriving at a formal proof, arguably the most difficult of formal reasoning tasks.

Reasoning, like habit or intuition, is one of the ways by which thinking moves from one idea to a related idea. For example, reasoning is the means by which rational individuals understand the significance of sensory information from their environments, or conceptualize abstract dichotomies such as cause and effect, truth and falsehood, or good and evil. Reasoning, as a part of executive decision making, is also closely identified with the ability to self-consciously change, in terms of goals, beliefs, attitudes, traditions, and institutions, and therefore with the capacity for freedom and self-determination.

In contrast to the use of "reason" as an abstract noun, a reason is a consideration that either explains or justifies events, phenomena, or behavior. Reasons justify decisions, reasons support explanations of natural phenomena, and reasons can be given to explain the actions (conduct) of individuals.

The words are connected in this way: Using reason, or reasoning, means providing good reasons. For example, when evaluating a moral decision, "morality is, at the very least, the effort to guide one's conduct by reason—that is, doing what there are the best reasons for doing—while giving equal [and impartial] weight to the interests of all those affected by what one does."

Psychologists and cognitive scientists have attempted to study and explain how people reason, e.g. which cognitive and neural processes are engaged, and how cultural factors affect the inferences that people draw. The field of automated reasoning studies how reasoning may or may not be modeled computationally. Animal psychology considers the question of whether animals other than humans can reason.

Etymology and related words
In the English language and other modern European languages, "reason", and related words, represent words which have always been used to translate Latin and classical Greek terms in their philosophical sense.
 * The original Greek term was "λόγος", the root of the modern English word "logic" but also a word that could mean for example "speech" or "explanation" or an "account" (of money handled).
 * As a philosophical term was translated in its non-linguistic senses in Latin as ratio. This was originally not just a translation used for philosophy, but was also commonly a translation for  in the sense of an account of money.
 * French raison is derived directly from Latin, and this is the direct source of the English word "reason".

The earliest major philosophers to publish in English, such as Francis Bacon, Thomas Hobbes, and John Locke also routinely wrote in Latin and French, and compared their terms to Greek, treating the words "", "ratio", "raison" and "reason" as interchangeable. The meaning of the word "reason" in senses such as "human reason" also overlaps to a large extent with "rationality" and the adjective of "reason" in philosophical contexts is normally "rational", rather than "reasoned" or "reasonable". Some philosophers, Thomas Hobbes for example, also used the word ratiocination as a synonym for "reasoning".

Philosophical history
The proposal that reason gives humanity a special position in nature has been argued to be a defining characteristic of western philosophy and later western science, starting with classical Greece. Philosophy can be described as a way of life based upon reason, while reason has been among the major subjects of philosophical discussion since ancient times. Reason is often said to be reflexive, or "self-correcting", and the critique of reason has been a persistent theme in philosophy.

Classical philosophy
For many classical philosophers, nature was understood teleologically, meaning that every type of thing had a definitive purpose that fit within a natural order that was itself understood to have aims. Perhaps starting with Pythagoras or Heraclitus, the cosmos was even said to have reason. Reason, by this account, is not just a characteristic that people happen to have. Reason was considered of higher stature than other characteristics of human nature, because it is something people share with nature itself, linking an apparently immortal part of the human mind with the divine order of the cosmos. Within the human mind or soul, reason was described by Plato as being the natural monarch which should rule over the other parts, such as spiritedness and the passions. Aristotle, Plato's student, defined human beings as rational animals, emphasizing reason as a characteristic of human nature. He described the highest human happiness or well being as a life which is lived consistently, excellently, and completely in accordance with reason.

The conclusions to be drawn from the discussions of Aristotle and Plato on this matter are amongst the most debated in the history of philosophy. But teleological accounts such as Aristotle's were highly influential for those who attempt to explain reason in a way that is consistent with monotheism and the immortality and divinity of the human soul. For example, in the neoplatonist account of Plotinus, the cosmos has one soul, which is the seat of all reason, and the souls of all people are part of this soul. Reason is for Plotinus both the provider of form to material things, and the light which brings people's souls back into line with their source.

Christian and Islamic philosophy
The classical view of reason, like many important Neoplatonic and Stoic ideas, was readily adopted by the early Church as the Church Fathers saw Greek Philosophy as an indispensable instrument given to mankind so that we may understand revelation. For example, the greatest among the early Church Fathers and Doctors of the Church such as Augustine of Hippo, Basil of Caesarea, and Gregory of Nyssa were as much Neoplatonic philosophers as they were Christian theologians, and they adopted the Neoplatonic view of human reason and its implications for our relationship to creation, to ourselves, and to God.

The Neoplatonic conception of the rational aspect of the human soul was widely adopted by medieval Islamic philosophers and continues to hold significance in Iranian philosophy. As European intellectual life reemerged from the Dark Ages, the Christian Patristic tradition and the influence of esteemed Islamic scholars like Averroes and Avicenna contributed to the development of the Scholastic view of reason, which laid the foundation for our modern understanding of this concept.

Among the Scholastics who relied on the classical concept of reason for the development of their doctrines, none were more influential than Saint Thomas Aquinas, who put this concept at the heart of his Natural Law. In this doctrine, Thomas concludes that because humans have reason and because reason is a spark of the divine, every single human life is invaluable, all humans are equal, and every human is born with an intrinsic and permanent set of basic rights. On this foundation, the idea of human rights would later be constructed by Spanish theologians at the School of Salamanca.

Other Scholastics, such as Roger Bacon and Albertus Magnus, following the example of Islamic scholars such as Alhazen, emphasised reason an intrinsic human ability to decode the created order and the structures that underlie our experienced physical reality. This interpretation of reason was instrumental to the development of the scientific method in the early Universities of the high Middle Ages.

Subject-centred reason in early modern philosophy
The early modern era was marked by a number of significant changes in the understanding of reason, starting in Europe. One of the most important of these changes involved a change in the metaphysical understanding of human beings. Scientists and philosophers began to question the teleological understanding of the world. Nature was no longer assumed to be human-like, with its own aims or reason, and human nature was no longer assumed to work according to anything other than the same "laws of nature" which affect inanimate things. This new understanding eventually displaced the previous world view that derived from a spiritual understanding of the universe. Accordingly, in the 17th century, René Descartes explicitly rejected the traditional notion of humans as "rational animals", suggesting instead that they are nothing more than "thinking things" along the lines of other "things" in nature. Any grounds of knowledge outside that understanding was, therefore, subject to doubt.

In his search for a foundation of all possible knowledge, Descartes decided to throw into doubt all knowledge—except that of the mind itself in the process of thinking:

"At this time I admit nothing that is not necessarily true. I am therefore precisely nothing but a thinking thing; that is a mind, or intellect, or understanding, or reason—words of whose meanings I was previously ignorant."

This eventually became known as epistemological or "subject-centred" reason, because it is based on the knowing subject, who perceives the rest of the world and itself as a set of objects to be studied, and successfully mastered, by applying the knowledge accumulated through such study. Breaking with tradition and with many thinkers after him, Descartes explicitly did not divide the incorporeal soul into parts, such as reason and intellect, describing them instead as one indivisible incorporeal entity.

A contemporary of Descartes, Thomas Hobbes described reason as a broader version of "addition and subtraction" which is not limited to numbers. This understanding of reason is sometimes termed "calculative" reason. Similar to Descartes, Hobbes asserted that "No discourse whatsoever, can end in absolute knowledge of fact, past, or to come" but that "sense and memory" is absolute knowledge.

In the late 17th century through the 18th century, John Locke and David Hume developed Descartes's line of thought still further. Hume took it in an especially skeptical direction, proposing that there could be no possibility of deducing relationships of cause and effect, and therefore no knowledge is based on reasoning alone, even if it seems otherwise.

Hume famously remarked that, "We speak not strictly and philosophically when we talk of the combat of passion and of reason. Reason is, and ought only to be the slave of the passions, and can never pretend to any other office than to serve and obey them." Hume also took his definition of reason to unorthodox extremes by arguing, unlike his predecessors, that human reason is not qualitatively different from either simply conceiving individual ideas, or from judgments associating two ideas, and that "reason is nothing but a wonderful and unintelligible instinct in our souls, which carries us along a certain train of ideas, and endows them with particular qualities, according to their particular situations and relations." It followed from this that animals have reason, only much less complex than human reason.

In the 18th century, Immanuel Kant attempted to show that Hume was wrong by demonstrating that a "transcendental" self, or "I", was a necessary condition of all experience. Therefore, suggested Kant, on the basis of such a self, it is in fact possible to reason both about the conditions and limits of human knowledge. And so long as these limits are respected, reason can be the vehicle of morality, justice, aesthetics, theories of knowledge (epistemology), and understanding.

Substantive and formal reason
In the formulation of Kant, who wrote some of the most influential modern treatises on the subject, the great achievement of reason (Vernunft) is that it is able to exercise a kind of universal law-making. Kant was able therefore to reformulate the basis of moral-practical, theoretical, and aesthetic reasoning on "universal" laws.

Here, practical reasoning is the self-legislating or self-governing formulation of universal norms, and theoretical reasoning is the way humans posit universal laws of nature.

Under practical reason, the moral autonomy or freedom of people depends on their ability, by the proper exercise of that reason, to behave according to laws that are given to them. This contrasted with earlier forms of morality, which depended on religious understanding and interpretation, or on nature, for their substance.

According to Kant, in a free society each individual must be able to pursue their goals however they see fit, as long as their actions conform to principles given by reason. He formulated such a principle, called the "categorical imperative", which would justify an action only if it could be universalized: "Act only according to that maxim whereby you can, at the same time, will that it should become a universal law."

In contrast to Hume, Kant insisted that reason itself (German Vernunft) could be used to find solutions to metaphysical problems, especially the discovery of the foundations of morality. Kant claimed that these solutions could be found with his "transcendental logic", which unlike normal logic is not just an instrument that can be used indifferently, as it was for Aristotle, but a theoretical science in its own right and the basis of all the others.

According to Jürgen Habermas, the "substantive unity" of reason has dissolved in modern times, such that it can no longer answer the question "How should I live?" Instead, the unity of reason has to be strictly formal, or "procedural". He thus described reason as a group of three autonomous spheres (on the model of Kant's three critiques):

 * Cognitive–instrumental reason: the kind of reason employed by the sciences; used to observe events, to predict and control outcomes, and to intervene in the world on the basis of its hypotheses
 * Moral–practical reason: what we use to deliberate and discuss issues in the moral and political realm, according to universalizable procedures (similar to Kant's categorical imperative)
 * Aesthetic reason: typically found in works of art and literature, and encompasses the novel ways of seeing the world and interpreting things that those practices embody

For Habermas, these three spheres are the domain of experts, and therefore need to be mediated with the "lifeworld" by philosophers. In drawing such a picture of reason, Habermas hoped to demonstrate that the substantive unity of reason, which in pre-modern societies had been able to answer questions about the good life, could be made up for by the unity of reason's formalizable procedures.

The critique of reason
Hamann, Herder, Kant, Hegel, Kierkegaard, Nietzsche, Heidegger, Foucault, Rorty, and many other philosophers have contributed to a debate about what reason means, or ought to mean. Some, like Kierkegaard, Nietzsche, and Rorty, are skeptical about subject-centred, universal, or instrumental reason, and even skeptical toward reason as a whole. Others, including Hegel, believe that it has obscured the importance of intersubjectivity, or "spirit" in human life, and they attempt to reconstruct a model of what reason should be.

Some thinkers, e.g. Foucault, believe there are other forms of reason, neglected but essential to modern life, and to our understanding of what it means to live a life according to reason. Others suggest that there is not just one reason or rationality, but multiple possible systems of reason or rationality which may conflict (in which case there is no super-rational system one can appeal to in order to resolve the conflict).

In the last several decades, a number of proposals have been made to "re-orient" this critique of reason, or to recognize the "other voices" or "new departments" of reason:

For example, in opposition to subject-centred reason, Habermas has proposed a model of communicative reason that sees it as an essentially cooperative activity, based on the fact of linguistic intersubjectivity.

Nikolas Kompridis proposed a widely encompassing view of reason as "that ensemble of practices that contributes to the opening and preserving of openness" in human affairs, and a focus on reason's possibilities for social change.

The philosopher Charles Taylor, influenced by the 20th century German philosopher Martin Heidegger, proposed that reason ought to include the faculty of disclosure, which is tied to the way we make sense of things in everyday life, as a new "department" of reason.

In the essay "What is Enlightenment?", Michel Foucault proposed a critique based on Kant's distinction between "private" and "public" uses of reason:
 * Private reason : the reason that is used when an individual is "a cog in a machine" or when one "has a role to play in society and jobs to do: to be a soldier, to have taxes to pay, to be in charge of a parish, to be a civil servant"
 * Public reason : the reason used "when one is reasoning as a reasonable being (and not as a cog in a machine), when one is reasoning as a member of reasonable humanity"; in these circumstances, "the use of reason must be free and public"

Reason compared to logic
The terms logic or logical are sometimes used as if they were identical with reason or rational, or sometimes logic is seen as the most pure or the defining form of reason: "Logic is about reasoning—about going from premises to a conclusion. ... When you do logic, you try to clarify reasoning and separate good from bad reasoning." In modern economics, rational choice is assumed to equate to logically consistent choice.

However, reason and logic can be thought of as distinct—although logic is one important aspect of reason. Author Douglas Hofstadter, in Gödel, Escher, Bach, characterizes the distinction in this way: Logic is done inside a system while reason is done outside the system by such methods as skipping steps, working backward, drawing diagrams, looking at examples, or seeing what happens if you change the rules of the system. Psychologists Mark H. Bickard and Robert L. Campbell argue that "rationality cannot be simply assimilated to logicality"; they note that "human knowledge of logic and logical systems has developed" over time through reasoning, and logical systems "can't construct new logical systems more powerful than themselves", so reasoning and rationality must involve more than a system of logic. Psychologist David Moshman, citing Bickhard and Campbell, argues for a "metacognitive conception of rationality" in which a person's development of reason "involves increasing consciousness and control of logical and other inferences".

Reason is a type of thought, and logic involves the attempt to describe a system of formal rules or norms of appropriate reasoning. The oldest surviving writing to explicitly consider the rules by which reason operates are the works of the Greek philosopher Aristotle, especially Prior Analytics and Posterior Analytics. Although the Ancient Greeks had no separate word for logic as distinct from language and reason, Aristotle's newly coined word "syllogism" identified logic clearly for the first time as a distinct field of study. When Aristotle referred to "the logical", he was referring more broadly to rational thought.

Reason compared to cause-and-effect thinking, and symbolic thinking
As pointed out by philosophers such as Hobbes, Locke, and Hume, some animals are also clearly capable of a type of "associative thinking", even to the extent of associating causes and effects. A dog once kicked, can learn how to recognize the warning signs and avoid being kicked in the future, but this does not mean the dog has reason in any strict sense of the word. It also does not mean that humans acting on the basis of experience or habit are using their reason.

Human reason requires more than being able to associate two ideas—even if those two ideas might be described by a reasoning human as a cause and an effect—perceptions of smoke, for example, and memories of fire. For reason to be involved, the association of smoke and the fire would have to be thought through in a way that can be explained, for example as cause and effect. In the explanation of Locke, for example, reason requires the mental use of a third idea in order to make this comparison by use of syllogism.

More generally, according to Charles Sanders Peirce, reason in the strict sense requires the ability to create and manipulate a system of symbols, as well as indices and icons, the symbols having only a nominal, though habitual, connection to either (for example) smoke or fire. One example of such a system of symbols and signs is language.

The connection of reason to symbolic thinking has been expressed in different ways by philosophers. Thomas Hobbes described the creation of "Markes, or Notes of remembrance" as speech. He used the word speech as an English version of the Greek word so that speech did not need to be communicated. When communicated, such speech becomes language, and the marks or notes or remembrance are called "Signes" by Hobbes. Going further back, although Aristotle is a source of the idea that only humans have reason, he does mention that animals with imagination, for whom sense perceptions can persist, come closest to having something like reasoning and , and even uses the word "" in one place to describe the distinctions which animals can perceive in such cases.

Reason, imagination, mimesis, and memory
Reason and imagination rely on similar mental processes. Imagination is not only found in humans. Aristotle asserted that (imagination: that which can hold images or ) and  (a type of thinking that can judge and understand in some sense) also exist in some animals. According to him, both are related to the primary perceptive ability of animals, which gathers the perceptions of different senses and defines the order of the things that are perceived without distinguishing universals, and without deliberation or. But this is not yet reason, because human imagination is different.

Terrence Deacon and Merlin Donald, writing about the origin of language, connect reason not only to language, but also mimesis. They describe the ability to create language as part of an internal modeling of reality, and specific to humankind. Other results are consciousness, and imagination or fantasy. In contrast, modern proponents of a genetic predisposition to language itself include Noam Chomsky and Steven Pinker.

If reason is symbolic thinking, and peculiarly human, then this implies that humans have a special ability to maintain a clear consciousness of the distinctness of "icons" or images and the real things they represent. Merlin Donald writes: "A dog might perceive the 'meaning' of a fight that was realistically play-acted by humans, but it could not reconstruct the message or distinguish the representation from its referent (a real fight).... Trained apes are able to make this distinction; young children make this distinction early—hence, their effortless distinction between play-acting an event and the event itself"

In classical descriptions, an equivalent description of this mental faculty is, in the philosophy of Plato. This is the ability to perceive whether a perception is an image of something else, related somehow but not the same, and therefore allows humans to perceive that a dream or memory or a reflection in a mirror is not reality as such. What Klein refers to as is the  concerned specifically with thinking and mental images, such as those mental symbols, icons, signes, and marks discussed above as definitive of reason. Explaining reason from this direction: human thinking is special in that we often understand visible things as if they were themselves images of our intelligible "objects of thought" as "foundations" ( in Ancient Greek). This thinking is "...an activity which consists in making the vast and diffuse jungle of the visible world depend on a plurality of more 'precise' ".

Both Merlin Donald and the Socratic authors such as Plato and Aristotle emphasize the importance of, often translated as imitation or representation. Donald writes: "Imitation is found especially in monkeys and apes [...but...] Mimesis is fundamentally different from imitation and mimicry in that it involves the invention of intentional representations.... Mimesis is not absolutely tied to external communication."

is a concept, now popular again in academic discussion, that was particularly prevalent in Plato's works. In Aristotle, it is discussed mainly in the Poetics. In Michael Davis's account of the theory of man in that work: "It is the distinctive feature of human action, that whenever we choose what we do, we imagine an action for ourselves as though we were inspecting it from the outside. Intentions are nothing more than imagined actions, internalizings of the external. All action is therefore imitation of action; it is poetic..."

Donald, like Plato (and Aristotle, especially in On Memory and Recollection), emphasizes the peculiarity in humans of voluntary initiation of a search through one's mental world. The ancient Greek, normally translated as "recollection" was opposed to or "memory". Memory, shared with some animals, requires a consciousness not only of what happened in the past, but also that something happened in the past, which is in other words a kind of "...but nothing except man is able to recollect." Recollection is a deliberate effort to search for and recapture something once known. Klein writes that, "To become aware of our having forgotten something means to begin recollecting." Donald calls the same thing autocueing, which he explains as follows: "Mimetic acts are reproducible on the basis of internal, self-generated cues. This permits voluntary recall of mimetic representations, without the aid of external cues—probably the earliest form of representational thinking."

In a celebrated paper, the fantasy author and philologist J.R.R. Tolkien wrote in his essay "On Fairy Stories" that the terms "fantasy" and "enchantment" are connected to not only "the satisfaction of certain primordial human desires" but also "the origin of language and of the mind".

Logical reasoning methods and argumentation
A subdivision of philosophy and a variety of reasoning is logic. The traditional main division made in philosophy is between deductive reasoning and inductive reasoning. Formal logic has been described as the science of deduction. The study of inductive reasoning is generally carried out within the field known as informal logic or critical thinking.

Deductive reasoning
Deduction is a form of reasoning in which a conclusion follows necessarily from the stated premises. A deduction is also the name for the conclusion reached by a deductive reasoning process. A classic example of deductive reasoning is evident in syllogisms like the following: The reasoning in this argument is deductively valid because there is no way in which both premises could be true and the conclusion be false.

Inductive reasoning
Induction is a form of inference that produces properties or relations about unobserved objects or types based on previous observations or experiences, or that formulates general statements or laws based on limited observations of recurring phenomenal patterns.

Inductive reasoning contrasts with deductive reasoning in that, even in the strongest cases of inductive reasoning, the truth of the premises does not guarantee the truth of the conclusion. Instead, the conclusion of an inductive argument follows with some degree of probability. For this reason also, the conclusion of an inductive argument contains more information than is already contained in the premises. Thus, this method of reasoning is ampliative.

A classic example of inductive reasoning comes from the empiricist David Hume:

Analogical reasoning
Analogical reasoning is a form of inductive reasoning from a particular to a particular. It is often used in case-based reasoning, especially legal reasoning. An example follows:

Analogical reasoning is a weaker form of inductive reasoning from a single example, because inductive reasoning typically uses a large number of examples to reason from the particular to the general. Analogical reasoning often leads to wrong conclusions. For example:

Abductive reasoning
Abductive reasoning, or argument to the best explanation, is a form of reasoning that does not fit in either the deductive or inductive categories, since it starts with incomplete set of observations and proceeds with likely possible explanations. The conclusion in an abductive argument does not follow with certainty from its premises and concerns something unobserved. What distinguishes abduction from the other forms of reasoning is an attempt to favour one conclusion above others, by subjective judgement or by attempting to falsify alternative explanations or by demonstrating the likelihood of the favoured conclusion, given a set of more or less disputable assumptions. For example, when a patient displays certain symptoms, there might be various possible causes, but one of these is preferred above others as being more probable.

Fallacious reasoning
Flawed reasoning in arguments is known as fallacious reasoning. Bad reasoning within arguments can result from either a formal fallacy or an informal fallacy.

Formal fallacies occur when there is a problem with the form, or structure, of the argument. The word "formal" refers to this link to the form of the argument. An argument that contains a formal fallacy will always be invalid.

An informal fallacy is an error in reasoning that occurs due to a problem with the content, rather than the form or structure, of the argument.

Unreasonable decisions and actions
In law relating to the actions of an employer or a public body, a decision or action which falls outside the range of actions or decision available when acting in good faith can be described as "unreasonable". Use of the term is considered in the English law cases of Short v Poole Corporation (1926), Associated Provincial Picture Houses Ltd v Wednesbury Corporation (1947) and Braganza v BP Shipping Limited (2015).

Traditional problems raised concerning reason
Philosophy is often characterized as a pursuit of rational understanding, entailing a more rigorous and dedicated application of human reasoning than commonly employed. Philosophers have long debated two fundamental questions regarding reason, essentially examining reasoning itself as a human endeavor, or philosophizing about philosophizing. The first question delves into whether we can place our trust in reason's ability to attain knowledge and truth more effectively than alternative methods. The second question explores whether a life guided by reason, a life that aims to be guided by reason, can be expected to lead to greater happiness compared to other approaches to life.

Reason versus truth, and "first principles"
Since classical antiquity a question has remained constant in philosophical debate (sometimes seen as a conflict between Platonism and Aristotelianism) concerning the role of reason in confirming truth. People use logic, deduction, and induction to reach conclusions they think are true. Conclusions reached in this way are considered, according to Aristotle, more certain than sense perceptions on their own. On the other hand, if such reasoned conclusions are only built originally upon a foundation of sense perceptions, then our most logical conclusions can never be said to be certain because they are built upon the very same fallible perceptions they seek to better.

This leads to the question of what types of first principles, or starting points of reasoning, are available for someone seeking to come to true conclusions. In Greek, "first principles" are, "starting points", and the faculty used to perceive them is sometimes referred to in Aristotle and Plato as which was close in meaning to awareness or consciousness.

Empiricism (sometimes associated with Aristotle but more correctly associated with British philosophers such as John Locke and David Hume, as well as their ancient equivalents such as Democritus) asserts that sensory impressions are the only available starting points for reasoning and attempting to attain truth. This approach always leads to the controversial conclusion that absolute knowledge is not attainable. Idealism, (associated with Plato and his school), claims that there is a "higher" reality, within which certain people can directly discover truth without needing to rely only upon the senses, and that this higher reality is therefore the primary source of truth.

Philosophers such as Plato, Aristotle, Al-Farabi, Avicenna, Averroes, Maimonides, Aquinas, and Hegel are sometimes said to have argued that reason must be fixed and discoverable—perhaps by dialectic, analysis, or study. In the vision of these thinkers, reason is divine or at least has divine attributes. Such an approach allowed religious philosophers such as Thomas Aquinas and Étienne Gilson to try to show that reason and revelation are compatible. According to Hegel, "...the only thought which Philosophy brings with it to the contemplation of History, is the simple conception of reason; that reason is the Sovereign of the World; that the history of the world, therefore, presents us with a rational process."

Since the 17th century rationalists, reason has often been taken to be a subjective faculty, or rather the unaided ability (pure reason) to form concepts. For Descartes, Spinoza, and Leibniz, this was associated with mathematics. Kant attempted to show that pure reason could form concepts (time and space) that are the conditions of experience. Kant made his argument in opposition to Hume, who denied that reason had any role to play in experience.

Reason versus emotion or passion
After Plato and Aristotle, western literature often treated reason as being the faculty that trained the passions and appetites. Stoic philosophy, by contrast, claimed most emotions were merely false judgements. According to the Stoics the only good is virtue, and the only evil is vice, therefore emotions that judged things other than vice to be bad (such as fear or distress), or things other than virtue to be good (such as greed) were simply false judgements and should be discarded (though positive emotions based on true judgements, such as kindness, were acceptable). After the critiques of reason in the early Enlightenment the appetites were rarely discussed or were conflated with the passions. Some Enlightenment camps took after the Stoics to say reason should oppose passion rather than order it, while others like the Romantics believed that passion displaces reason, as in the maxim "follow your heart".

Reason has been seen as cold, an "enemy of mystery and ambiguity", a slave, or judge, of the passions, notably in the work of David Hume, and more recently of Freud.

Reasoning that claims the object of a desire is demanded by logic alone is called rationalization.

Rousseau first proposed, in his second Discourse, that reason and political life is not natural and is possibly harmful to mankind. He asked what really can be said about what is natural to mankind. What, other than reason and civil society, "best suits his constitution"? Rousseau saw "two principles prior to reason" in human nature. First we hold an intense interest in our own well-being. Secondly we object to the suffering or death of any sentient being, especially one like ourselves. These two passions lead us to desire more than we could achieve. We become dependent upon each other, and on relationships of authority and obedience. This effectively puts the human race into slavery. Rousseau says that he almost dares to assert that nature does not destine men to be healthy. According to Richard Velkley, "Rousseau outlines certain programs of rational self-correction, most notably the political legislation of the Contrat Social and the moral education in Émile. All the same, Rousseau understands such corrections to be only ameliorations of an essentially unsatisfactory condition, that of socially and intellectually corrupted humanity."

This quandary presented by Rousseau led to Kant's new way of justifying reason as freedom to create good and evil. These therefore are not to be blamed on nature or God. In various ways, German Idealism after Kant, and major later figures such Nietzsche, Bergson, Husserl, Scheler, and Heidegger, remain preoccupied with problems coming from the metaphysical demands or urges of reason. Rousseau and these later writers also exerted a large influence on art and politics. Many writers (such as Nikos Kazantzakis) extol passion and disparage reason. In politics modern nationalism comes from Rousseau's argument that rationalist cosmopolitanism brings man ever further from his natural state.

In Descartes' Error, Antonio Damasio presents the "Somatic Marker Hypothesis" which states that emotions guide behavior and decision-making. Damasio argues that these somatic markers (known collectively as "gut feelings") are "intuitive signals" that direct our decision making processes in a certain way that cannot be solved with rationality alone. Damasio further argues that rationality requires emotional input in order to function.

Reason versus faith or tradition
There are many religious traditions, some of which are explicitly fideist and others of which claim varying degrees of rationalism. Secular critics sometimes accuse all religious adherents of irrationality; they claim such adherents are guilty of ignoring, suppressing, or forbidding some kinds of reasoning concerning some subjects (such as religious dogmas, moral taboos, etc.). Though theologies and religions such as classical monotheism typically do not admit to being irrational, there is often a perceived conflict or tension between faith and tradition on the one hand, and reason on the other, as potentially competing sources of wisdom, law, and truth.

Religious adherents sometimes respond by arguing that faith and reason can be reconciled, or have different non-overlapping domains, or that critics engage in a similar kind of irrationalism:
 * Reconciliation : Philosopher Alvin Plantinga argues that there is no real conflict between reason and classical theism because classical theism explains (among other things) why the universe is intelligible and why reason can successfully grasp it.
 * Non-overlapping magisteria : Evolutionary biologist Stephen Jay Gould argues that there need not be conflict between reason and religious belief because they are each authoritative in their own domain (or "magisterium"). If so, reason can work on those problems over which it has authority while other sources of knowledge or opinion can have authority on the big questions.
 * Tu quoque : Philosophers Alasdair MacIntyre and Charles Taylor argue that those critics of traditional religion who are adherents of secular liberalism are also sometimes guilty of ignoring, suppressing, and forbidding some kinds of reasoning about subjects. Similarly, philosophers of science such as Paul Feyarabend argue that scientists sometimes ignore or suppress evidence contrary to the dominant paradigm.
 * Unification : Theologian Joseph Ratzinger, later Benedict XVI, asserted that "Christianity has understood itself as the religion of the Logos, as the religion according to reason," referring to Ἐν ἀρχῇ ἦν ὁ λόγος, usually translated as "In the beginning was the Word (Logos)." Thus, he said that the Christian faith is "open to all that is truly rational", and that the rationality of Western Enlightenment "is of Christian origin".

Some commentators have claimed that Western civilization can be almost defined by its serious testing of the limits of tension between "unaided" reason and faith in "revealed" truths—figuratively summarized as Athens and Jerusalem, respectively. Leo Strauss spoke of a "Greater West" that included all areas under the influence of the tension between Greek rationalism and Abrahamic revelation, including the Muslim lands. He was particularly influenced by the Muslim philosopher Al-Farabi. To consider to what extent Eastern philosophy might have partaken of these important tensions, Strauss thought it best to consider whether dharma or tao may be equivalent to Nature ( in Greek). According to Strauss the beginning of philosophy involved the "discovery or invention of nature" and the "pre-philosophical equivalent of nature" was supplied by "such notions as 'custom' or 'ways, which appear to be really universal in all times and places. The philosophical concept of nature or natures as a way of understanding (first principles of knowledge) brought about a peculiar tension between reasoning on the one hand, and tradition or faith on the other.

Psychology and cognitive science
Scientific research into reasoning is carried out within the fields of psychology and cognitive science. Psychologists attempt to determine whether or not people are capable of rational thought in a number of different circumstances.

Assessing how well someone engages in reasoning is the project of determining the extent to which the person is rational or acts rationally. It is a key research question in the psychology of reasoning and cognitive science of reasoning. Rationality is often divided into its respective theoretical and practical counterparts.

Behavioral experiments on human reasoning
Experimental cognitive psychologists carry out research on reasoning behaviour. Such research may focus, for example, on how people perform on tests of reasoning such as intelligence or IQ tests, or on how well people's reasoning matches ideals set by logic (see, for example, the Wason test). Experiments examine how people make inferences from conditionals like if A then B and how they make inferences about alternatives like A or else B. They test whether people can make valid deductions about spatial and temporal relations like A is to the left of B or A happens after B, and about quantified assertions like all the A are B. Experiments investigate how people make inferences about factual situations, hypothetical possibilities, probabilities, and counterfactual situations.

Developmental studies of children's reasoning
Developmental psychologists investigate the development of reasoning from birth to adulthood. Piaget's theory of cognitive development was the first complete theory of reasoning development. Subsequently, several alternative theories were proposed, including the neo-Piagetian theories of cognitive development.

Neuroscience of reasoning
The biological functioning of the brain is studied by neurophysiologists, cognitive neuroscientists, and neuropsychologists. This includes research into the structure and function of normally functioning brains, and of damaged or otherwise unusual brains. In addition to carrying out research into reasoning, some psychologists—for example clinical psychologists and psychotherapists—work to alter people's reasoning habits when those habits are unhelpful.

Automated reasoning
In artificial intelligence and computer science, scientists study and use automated reasoning for diverse applications including automated theorem proving the formal semantics of programming languages, and formal specification in software engineering.

Meta-reasoning
Meta-reasoning is reasoning about reasoning. In computer science, a system performs meta-reasoning when it is reasoning about its own operation. This requires a programming language capable of reflection, the ability to observe and modify its own structure and behaviour.

Evolution of reason
A species could benefit greatly from better abilities to reason about, predict, and understand the world. French social and cognitive scientists Dan Sperber and Hugo Mercier argue that, aside from these benefits, there could have been other forces driving the evolution of reason. They point out that reasoning is very difficult for humans to do effectively, and that it is hard for individuals to doubt their own beliefs (confirmation bias). Reasoning is most effective when it is done as a collective—as demonstrated by the success of projects like science. They suggest that there are not just individual, but group selection pressures at play. Any group that managed to find ways of reasoning effectively would reap benefits for all its members, increasing their fitness. This could also help explain why humans, according to Sperber, are not optimized to reason effectively alone. Sperber's & Mercier's argumentative theory of reasoning claims that reason may have more to do with winning arguments than with the search for the truth.

Reason in political philosophy and ethics
Aristotle famously described reason (with language) as a part of human nature, because of which it is best for humans to live "politically" meaning in communities of about the size and type of a small city state ( in Greek). For example: "It is clear, then, that a human being is more of a political = of the ] animal [] than is any bee or than any of those animals that live in herds. For nature, as we say, makes nothing in vain, and humans are the only animals who possess reasoned speech []. Voice, of course, serves to indicate what is painful and pleasant; that is why it is also found in other animals, because their nature has reached the point where they can perceive what is painful and pleasant and express these to each other. But speech [] serves to make plain what is advantageous and harmful and so also what is just and unjust. For it is a peculiarity of humans, in contrast to the other animals, to have perception of good and bad, just and unjust, and the like; and the community in these things makes a household or city [].... By nature, then, the drive for such a community exists in everyone, but the first to set one up is responsible for things of very great goodness. For as humans are the best of all animals when perfected, so they are the worst when divorced from law and right. The reason is that injustice is most difficult to deal with when furnished with weapons, and the weapons a human being has are meant by nature to go along with prudence and virtue, but it is only too possible to turn them to contrary uses. Consequently, if a human being lacks virtue, he is the most unholy and savage thing, and when it comes to sex and food, the worst. But justice is something political [to do with the ], for right is the arrangement of the political community, and right is discrimination of what is just."

If human nature is fixed in this way, we can define what type of community is always best for people. This argument has remained a central argument in all political, ethical, and moral thinking since then, and has become especially controversial since firstly Rousseau's Second Discourse, and secondly, the Theory of Evolution. Already in Aristotle there was an awareness that the had not always existed and had to be invented or developed by humans themselves. The household came first, and the first villages and cities were just extensions of that, with the first cities being run as if they were still families with Kings acting like fathers. "Friendship seems to prevail in man and woman according to nature []; for people are by nature [] pairing more than political [], in as much as the household [] is prior and more necessary than the and making children is more common [] with the animals. In the other animals, community [] goes no further than this, but people live together [] not only for the sake of making children, but also for the things for life; for from the start the functions [] are divided, and are different for man and woman. Thus they supply each other, putting their own into the common []. It is for these reasons that both utility and pleasure seem to be found in this kind of friendship."

Rousseau in his Second Discourse finally took the shocking step of claiming that this traditional account has things in reverse: with reason, language, and rationally organized communities all having developed over a long period of time merely as a result of the fact that some habits of cooperation were found to solve certain types of problems, and that once such cooperation became more important, it forced people to develop increasingly complex cooperation—often only to defend themselves from each other.

In other words, according to Rousseau, reason, language, and rational community did not arise because of any conscious decision or plan by humans or gods, nor because of any pre-existing human nature. As a result, he claimed, living together in rationally organized communities like modern humans is a development with many negative aspects compared to the original state of man as an ape. If anything is specifically human in this theory, it is the flexibility and adaptability of humans. This view of the animal origins of distinctive human characteristics later received support from Charles Darwin's Theory of Evolution.

The two competing theories concerning the origins of reason are relevant to political and ethical thought because, according to the Aristotelian theory, a best way of living together exists independently of historical circumstances. According to Rousseau, we should even doubt that reason, language, and politics are a good thing, as opposed to being simply the best option given the particular course of events that led to today. Rousseau's theory, that human nature is malleable rather than fixed, is often taken to imply (for example by Karl Marx) a wider range of possible ways of living together than traditionally known.

However, while Rousseau's initial impact encouraged bloody revolutions against traditional politics, including both the French Revolution and the Russian Revolution, his own conclusions about the best forms of community seem to have been remarkably classical, in favor of city-states such as Geneva, and rural living.

title: Reason


text:
Pentaerythritol tetranitrate

Pentaerythritol tetranitrate (PETN), also known as PENT, pentyl, PENTA (ПЕНТА, primarily in Russian), TEN (tetraeritrit nitrate), corpent, or penthrite (or, rarely and primarily in German, as nitropenta), is an explosive material. It is the nitrate ester of pentaerythritol, and is structurally very similar to nitroglycerin. Penta refers to the five carbon atoms of the neopentane skeleton. PETN is a very powerful explosive material with a relative effectiveness factor of 1.66. When mixed with a plasticizer, PETN forms a plastic explosive. Along with RDX it is the main ingredient of Semtex and C4.

PETN is also used as a vasodilator drug to treat certain heart conditions, such as for management of angina.

History
Pentaerythritol tetranitrate was first prepared and patented in 1894 by the explosives manufacturer of Cologne, Germany. The production of PETN started in 1912, when the improved method of production was patented by the German government. PETN was used by the German Military in World War I. It was also used in the MG FF/M autocannons and many other weapon systems of the Luftwaffe in World War II.

Properties
PETN is practically insoluble in water (0.01 g/100 mL at 50 °C), weakly soluble in common nonpolar solvents such as aliphatic hydrocarbons (like gasoline) or tetrachloromethane, but soluble in some other organic solvents, particularly in acetone (about 15 g/100 g of the solution at 20 °C, 55 g/100 g at 60 °C) and dimethylformamide (40 g/100 g of the solution at 40 °C, 70 g/100 g at 70 °C). PETN forms eutectic mixtures with some liquid or molten aromatic nitro compounds, e.g. trinitrotoluene (TNT) or tetryl. Due to steric hindrance of the adjacent neopentyl-like moiety, PETN is resistant to attack by many chemical reagents; it does not hydrolyze in water at room temperature or in weaker alkaline aqueous solutions. Water at 100 °C or above causes hydrolysis to dinitrate; presence of 0.1% nitric acid accelerates the reaction.

The chemical stability of PETN is of interest, because of the presence of PETN in aging weapons. Neutron radiation degrades PETN, producing carbon dioxide and some pentaerythritol dinitrate and trinitrate. Gamma radiation increases the thermal decomposition sensitivity of PETN, lowers melting point by few degrees Celsius, and causes swelling of the samples. Like other nitrate esters, the primary degradation mechanism is the loss of nitrogen dioxide; this reaction is autocatalytic. Studies were performed on thermal decomposition of PETN.

In the environment, PETN undergoes biodegradation. Some bacteria denitrate PETN to trinitrate and then dinitrate, which is then further degraded. PETN has low volatility and low solubility in water, and therefore has low bioavailability for most organisms. Its toxicity is relatively low, and its transdermal absorption also seems to be low. It poses a threat for aquatic organisms. It can be degraded to pentaerythritol by iron.

Production
Production is by the reaction of pentaerythritol with concentrated nitric acid to form a precipitate which can be recrystallized from acetone to give processable crystals.

Variations of a method first published in US Patent 2,370,437 by Acken and Vyverberg (1945 to Du Pont) form the basis of all current commercial production.

PETN is manufactured by numerous manufacturers as a powder, or together with nitrocellulose and plasticizer as thin plasticized sheets (e.g. Primasheet 1000 or Detasheet). PETN residues are easily detectable in hair of people handling it. The highest residue retention is on black hair; some residues remain even after washing.

Explosive use

The most common use of PETN is as an explosive with high brisance. It is a secondary explosive, meaning it is more difficult to detonate than primary explosives, so dropping or igniting it will typically not cause an explosion (at standard atmospheric pressure it is difficult to ignite and burns vigorously), but is more sensitive to shock and friction than other secondary explosives such as TNT or tetryl. Under certain conditions a deflagration to detonation transition can occur, just like that of ammonium nitrate.

It is rarely used alone in military operations due to its lower stability, but primarily used in main charges of plastic explosives such as C4 along with other explosives (especially RDX), booster and bursting charges of small caliber ammunition, in upper charges of detonators in some land mines and shells, as the explosive core of detonation cord. PETN is the least stable of the common military explosives, but can be stored without significant deterioration for longer than nitroglycerin or nitrocellulose.

During World War II, PETN was most importantly used in exploding-bridgewire detonators for the atomic bombs. These exploding-bridgewire detonators gave more precise detonation, compared with primacord. PETN was used for these detonators because it was safer than primary explosives like lead azide: while it was sensitive, it would not detonate below a threshold amount of energy. Exploding bridgewires containing PETN remain used in current nuclear weapons. In spark detonators, PETN is used to avoid the need for primary explosives; the energy needed for a successful direct initiation of PETN by an electric spark ranges between 10–60 mJ.

Its basic explosion characteristics are:
 * Explosion energy: 5810 kJ/kg (1390 kcal/kg), so 1 kg of PETN has the energy of 1.24 kg TNT.
 * Detonation velocity: 8350 m/s (1.73 g/cm3), 7910 m/s (1.62 g/cm3), 7420 m/s (1.5 g/cm3), 8500 m/s (pressed in a steel tube)
 * Volume of gases produced: 790 dm3/kg (other value: 768 dm3/kg)
 * Explosion temperature: 4230 °C
 * Oxygen balance: −6.31 atom -g/kg
 * Melting point: 141.3 °C (pure), 140–141 °C (technical)
 * Trauzl lead block test: 523 cm3 (other values: 500 cm3 when sealed with sand, or 560 cm3 when sealed with water)
 * Critical diameter (minimal diameter of a rod that can sustain detonation propagation): 0.9 mm for PETN at 1 g/cm3, smaller for higher densities (other value: 1.5 mm)

In mixtures
PETN is used in a number of compositions. It is a major ingredient of the Semtex plastic explosive. It is also used as a component of pentolite, a 50/50 blend with TNT. The XTX8003 extrudable explosive, used in the W68 and W76 nuclear warheads, is a mixture of 80% PETN and 20% of Sylgard 182, a silicone rubber. It is often phlegmatized by addition of 5–40% of wax, or by polymers (producing polymer-bonded explosives); in this form it is used in some cannon shells up to 30 mm caliber, though it is unsuitable for higher calibers. It is also used as a component of some gun propellants and solid rocket propellants. Nonphlegmatized PETN is stored and handled with approximately 10% water content. PETN alone cannot be cast as it explosively decomposes slightly above its melting point, but it can be mixed with other explosives to form castable mixtures.

PETN can be initiated by a laser. A pulse with duration of 25 nanoseconds and 0.5–4.2 joules of energy from a Q-switched ruby laser can initiate detonation of a PETN surface coated with a 100 nm thick aluminium layer in less than half of a microsecond.

PETN has been replaced in many applications by RDX, which is thermally more stable and has a longer shelf life. PETN can be used in some ram accelerator types. Replacement of the central carbon atom with silicon produces Si-PETN, which is extremely sensitive.

Terrorist use
Ten kilograms of PETN was used in the 1980 Paris synagogue bombing.

In 1983, 307 people were killed after a truck bomb filled with PETN was detonated at the Beirut barracks.

In 1983, the "Maison de France" house in Berlin was brought to a near-total collapse by the detonation of 24 kg of PETN by terrorist Johannes Weinrich.

In 1999, Alfred Heinz Reumayr used PETN as the main charge for his fourteen improvised explosive devices that he constructed in a thwarted attempt to damage the Trans-Alaska Pipeline System.

In 2001, al-Qaeda member Richard Reid, the "Shoe Bomber", used PETN in the sole of his shoe in his unsuccessful attempt to blow up American Airlines Flight 63 from Paris to Miami. He had intended to use the solid triacetone triperoxide (TATP) as a detonator.

In 2009, PETN was used in an attempt by al-Qaeda in the Arabian Peninsula to murder the Saudi Arabian Deputy Minister of Interior Prince Muhammad bin Nayef, by Saudi suicide bomber Abdullah Hassan al Asiri. The target survived and the bomber died in the blast. The PETN was hidden in the bomber's rectum, which security experts described as a novel technique.

On 25 December 2009, PETN was found in the underwear of Umar Farouk Abdulmutallab, the "Underwear bomber", a Nigerian with links to al-Qaeda in the Arabian Peninsula. According to US law enforcement officials, he had attempted to blow up Northwest Airlines Flight 253 while approaching Detroit from Amsterdam. Abdulmutallab had tried, unsuccessfully, to detonate approximately 80 g of PETN sewn into his underwear by adding liquid from a syringe; however, only a small fire resulted.

In the al-Qaeda in the Arabian Peninsula October 2010 cargo plane bomb plot, two PETN-filled printer cartridges were found at East Midlands Airport and in Dubai on flights bound for the US on an intelligence tip. Both packages contained sophisticated bombs concealed in computer printer cartridges filled with PETN. The bomb found in England contained 400 g of PETN, and the one found in Dubai contained 300 g of PETN. Hans Michels, professor of safety engineering at University College London, told a newspaper that 6 g of PETN—"around 50 times less than was used—would be enough to blast a hole in a metal plate twice the thickness of an aircraft's skin". In contrast, according to an experiment conducted by a BBC documentary team designed to simulate Abdulmutallab's Christmas Day bombing, using a Boeing 747 plane, even 80 grams of PETN was not sufficient to materially damage the fuselage.

On 12 July 2017, 150 grams of PETN was found in the Assembly of Uttar Pradesh, India's most populous state.

Detection
In the wake of terrorist PETN bomb plots, an article in Scientific American noted PETN is difficult to detect because it does not readily vaporize into the surrounding air. The Los Angeles Times noted in November 2010 that PETN's low vapor pressure makes it difficult for bomb-sniffing dogs to detect.

Many technologies can be used to detect PETN, including chemical sensors, X-rays, infrared, microwaves and terahertz, some of which have been implemented in public screening applications, primarily for air travel. PETN is one of the explosive chemicals typically of interest in that area, and it belongs to a family of common nitrate-based explosive chemicals which can often be detected by the same tests.

One detection system in use at airports involves analysis of swab samples obtained from passengers and their baggage. Whole-body imaging scanners that use radio-frequency electromagnetic waves, low-intensity X-rays, or T-rays of terahertz frequency that can detect objects hidden under clothing are not widely used because of cost, concerns about the resulting traveler delays, and privacy concerns.

Both parcels in the 2010 cargo plane bomb plot were x-rayed without the bombs being spotted. Qatar Airways said the PETN bomb "could not be detected by x-ray screening or trained sniffer dogs". The Bundeskriminalamt received copies of the Dubai x-rays, and an investigator said German staff would not have identified the bomb either. New airport security procedures followed in the U.S., largely to protect against PETN.

Medical use
Like nitroglycerin (glyceryl trinitrate) and other nitrates, PETN is also used medically as a vasodilator in the treatment of heart conditions. These drugs work by releasing the signaling gas nitric oxide in the body. The heart medicine Lentonitrat is nearly pure PETN.

Monitoring of oral usage of the drug by patients has been performed by determination of plasma levels of several of its hydrolysis products, pentaerythritol dinitrate, pentaerythritol mononitrate and pentaerythritol, in plasma using gas chromatography-mass spectrometry.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Pentaerythritol tetranitrate


text:
Kirkendall effect

The Kirkendall effect is the motion of the interface between two metals that occurs due to the difference in diffusion rates of the metal atoms. The effect can be observed for example by placing insoluble markers at the interface between a pure metal and an alloy containing that metal, and heating to a temperature where atomic diffusion is reasonable for the given timescale; the boundary will move relative to the markers.

This process was named after Ernest Kirkendall (1914–2005), assistant professor of chemical engineering at Wayne State University from 1941 to 1946. The paper describing the discovery of the effect was published in 1947.

The Kirkendall effect has important practical consequences. One of these is the prevention or suppression of voids formed at the boundary interface in various kinds of alloy to metal bonding. These are referred to as Kirkendall voids.

History
The Kirkendall effect was discovered by Ernest Kirkendall and Alice Smigelskas in 1947, in the course of Kirkendall's ongoing research into diffusion in brass. The paper in which he discovered the famous effect was the third in his series of papers on brass diffusion, the first being his thesis. His second paper revealed that zinc diffused more quickly than copper in alpha-brass, which led to the research producing his revolutionary theory. Until this point, substitutional and ring methods were the dominant ideas for diffusional motion. Kirkendall's experiment produced evidence of a vacancy diffusion mechanism, which is the accepted mechanism to this day. At the time it was submitted, the paper and Kirkendall's ideas were rejected from publication by Robert Franklin Mehl, director of the Metals Research Laboratory at Carnegie Institute of Technology (now Carnegie Mellon University). Mehl refused to accept Kirkendall's evidence of this new diffusion mechanism, and denied publication for over six months, only relenting after a conference was held and several other researchers confirmed Kirkendall's results.

Kirkendall's experiment
A bar of brass (70% Cu, 30% Zn) was used as a core, with molybdenum wires stretched along its length, and then coated in a layer of pure copper. Molybdenum was chosen as the marker material due to it being very insoluble in brass, eliminating any error due to the markers diffusing themselves. Diffusion was allowed to take place at 785 °C over the course of 56 days, with cross-sections being taken at six times throughout the span of the experiment. Over time, it was observed that the wire markers moved closer together as the zinc diffused out of the brass and into the copper. A difference in location of the interface was visible in cross sections of different times. Compositional change of the material from diffusion was confirmed by x-ray diffraction.

Diffusion mechanism
Early diffusion models postulated that atomic motion in substitutional alloys occurs via a direct exchange mechanism, in which atoms migrate by switching positions with atoms on adjacent lattice sites. Such a mechanism implies that the atomic fluxes of two different materials across an interface must be equal, as each atom moving across the interface causes another atom to move across in the other direction.

Another possible diffusion mechanism involves lattice vacancies. An atom can move into a vacant lattice site, effectively causing the atom and the vacancy to switch places. If large-scale diffusion takes place in a material, there will be a flux of atoms in one direction and a flux of vacancies in the other.

The Kirkendall effect arises when two distinct materials are placed next to each other and diffusion is allowed to take place between them. In general, the diffusion coefficients of the two materials in each other are not the same. This is only possible if diffusion occurs by a vacancy mechanism; if the atoms instead diffused by an exchange mechanism, they would cross the interface in pairs, so the diffusion rates would be identical, contrary to observation. By Fick's 1st law of diffusion, the flux of atoms from the material with the higher diffusion coefficient will be larger, so there will be a net flux of atoms from the material with the higher diffusion coefficient into the material with the lower diffusion coefficient. To balance this flux of atoms, there will be a flux of vacancies in the opposite direction—from the material with the lower diffusion coefficient into the material with the higher diffusion coefficient—resulting in an overall translation of the lattice relative to the environment in the direction of the material with the lower diffusion constant.

Macroscopic evidence for the Kirkendall effect can be gathered by placing inert markers at the initial interface between the two materials, such as molybdenum markers at an interface between copper and brass. The diffusion coefficient of zinc is higher than the diffusion coefficient of copper in this case. Since zinc atoms leave the brass at a higher rate than copper atoms enter, the size of the brass region decreases as diffusion progresses. Relative to the molybdenum markers, the copper-brass interface moves toward the brass at an experimentally measurable rate.

Darken's equations
Shortly after the publication of Kirkendall's paper, L.S. Darken published an analysis of diffusion in binary systems much like the one studied by Smigelskas and Kirkendall. By separating the actual diffusive flux of the materials from the movement of the interface relative to the markers, Darken found the marker velocity $$v$$ to be $v = (D_1-D_2)\frac{dN_1}{dx},$ where $$D_1$$ and $$D_2$$ are the diffusion coefficients of the two materials and $$N_1$$ is an atomic fraction. One consequence of this equation is that the movement of an interface varies linearly with the square root of time, which is exactly the experimental relationship discovered by Smigelskas and Kirkendall.

Darken also developed a second equation that defines a combined chemical diffusion coefficient $$D$$ in terms of the diffusion coefficients of the two interfacing materials: $D = N_1 D_2 + N_2 D_1.$ This chemical diffusion coefficient can be used to mathematically analyze Kirkendall effect diffusion via the Boltzmann-Matano method.

Kirkendall porosity
One important consideration deriving from Kirkendall's work is the presence of pores formed during diffusion. These voids act as sinks for vacancies, and when enough accumulate they can become substantial and expand in an attempt to restore equilibrium. Porosity occurs due to the difference in diffusion rate of the two species.

Pores in metals have ramifications for mechanical, thermal, and electrical properties, and thus control over their formation is often desired. The equation $X^K = (a_1 \Delta C_1^\circ + a_2 \Delta C_2^\circ + \dots + a_{n-1} \Delta C_{n-1}^\circ)\sqrt{t}$ where $$X^K$$ is the distance moved by a marker, $$a$$ is a coefficient determined by intrinsic diffusivities of the materials, and $$\Delta C^\circ$$ is a concentration difference between components, has proven to be an effective model for mitigating Kirkendall porosity. Controlling annealing temperature is another method of reducing or eliminating porosity. Kirkendall porosity typically occurs at a set temperature in a system, so annealing can be performed at lower temperatures for longer times to avoid formation of pores.

Examples
In 1972, C.W. Horsting of the RCA Corporation published a paper which reported test results on the reliability of semiconductor devices in which the connections were made using aluminium wires bonded ultrasonically to gold plated posts. His paper demonstrated the importance of the Kirkendall effect in wire bonding technology, but also showed the significant contribution of any impurities present to the rate at which precipitation occurred at the wire bonds. Two of the important contaminants that have this effect, known as Horsting effect (Horsting voids) are fluorine and chlorine. Both Kirkendall voids and Horsting voids are known causes of wire bond fractures, though historically this cause is often confused with the purple colored appearance of one of the five different gold-aluminium intermetallics, commonly referred to as "purple plague" and less often "white plague".

title: Kirkendall effect


text:
1063

Year 1063 (MLXIII) was a common year starting on Wednesday (link will display the full calendar) of the Julian calendar.

Europe

 * May 8 – Battle of Graus: Allied Muslim and Christian troops, under King Sancho II (the Strong) and Emir Ahmad al-Muqtadir (maybe led by El Cid), defeat the Aragonese army. King Ramiro I is killed and succeeded by his son Sancho V, as ruler of Aragon.
 * Battle of Cerami: Duke Roger I leads a small Norman force (supported by 136 mounted knights), and defeats a much larger Saracen army (35,000 men) at Cerami (near Troina) in Sicily.
 * Summer – The Pisan fleet assaults and sacks Palermo (controlled by the Saracens) – this in support of the Norman forces of Roger I.
 * August–September: The Holy Roman Empire invades Hungary and installs Solomon as their proxy ruler.
 * Duke William I (the Bastard) claims the province of Maine and betroths his son Robert to Margaret, daughter of late Count Herbert II.

Seljuk Empire

 * Battle of Damghan: Seljuk forces under Alp Arslan defeat his brother Qutalmish who claims the throne of late Tughril, founder of the Seljuk Empire. Qutalmish flees from the battle, but his son Suleiman is taken prisoner.

Architecture

 * The Pizhi Pagoda located at Lingyan Temple (Shandong province) in China is completed, standing at a height of 54 m (177 ft) tall.
 * Doge Domenico I orders the construction of the present building of St Mark's Basilica at Venice (approximate date).

Religion

 * Anselm, later to become archbishop of Canterbury, becomes prior at the Abbey of Bec (approximate date).
 * The bishopric of Olomouc (located on the River Morava) is founded (modern Czech Republic).

Births

 * Eight Deer Jaguar Claw (or 8 Deer), Mixtec ruler (d. 1115)
 * Yuanwu Keqin, Chinese Chan Buddhist monk (d. 1135)

Deaths

 * March 21 – Richeza of Lotharingia, queen of Poland
 * April 30 – Ren Zong, emperor of the Song Dynasty (b. 1010)
 * May 8 – Ramiro I, king of Aragon (House of Jiménez)
 * August 5 – Gruffydd ap Llywelyn, king of Gwynedd
 * August 9 – Constantine III, Byzantine patriarch
 * September 3 – Henry II, archbishop of Augsburg
 * September 4 – Tughril, sultan of the Seljuk Empire (b. 990)
 * September 11 – Béla I (the Champion), king of Hungary
 * December 7 – Qutalmish, prince of the Seljuk Empire
 * Gotebald (or Gotebold), patriarch of Aquileia
 * Hedwig (or Advisa), countess of Nevers
 * Hilduin IV, count of Montdidier and Roucy
 * Pang Ji, Chinese official and chancellor (b. 988)
 * Sudislav Vladimirovich, prins of Pskov
 * Sylvester III, pope of the Catholic Church

title: 1063


text:
1064

Year 1064 (MLXIV) was a leap year starting on Thursday (link will display the full calendar) of the Julian calendar.

Europe

 * Summer – King Ferdinand I (the Great) conquers more territory in modern-day Portugal and captures Coimbra. He appoints Sisnando Davides to reorganise the economy and administer the lands encircling the city.
 * European warriors go to Spain, to participate in the siege of Barbastro. This expedition is sanctioned by Pope Alexander II – and is now regarded as an early form of Crusade.
 * Harold Godwinson, Earl of Wessex, is shipwrecked on the shores of Ponthieu (Normandy). He is captured by Count Guy I who takes him as hostage to his castle of Beaurian.
 * Duke William I (the Bastard) demands the release of Harold Godwinson from Guy I (after a ransom being paid). Harold must swear an oath to aid William to the throne of England.
 * Kings Harald Hardrada of Norway and Sweyn II of Denmark agree to a peace agreement. Harald turns his attentions to England where he believes he has a right to the throne.

Seljuk Empire

 * April 27 – Alp Arslan succeeds to the throne, as sultan of the Seljuk Empire. He becomes sole ruler of Persia from the river Oxus to the Tigris.
 * The Seljuk Turks under Alp Arslan invade Anatolia, and capture Ani after a siege of 25-days. He sacks the city and slaughters its citizens.
 * Badr al-Jamali, Fatimid governor of Syria, tries to engineer a pro-Fatimid coup in Aleppo; but the rebellion is suppressed by Musa Yabgu.

Asia

 * King Bagrat IV of Georgia captures the fortress city of Samshvilde, the capital of the neighboring Tashir-Dzoraget.

Mesoamerica

 * January 4 – The Aztecs migrate from Aztlán to the southern lands in central Mexico.

Religion

 * Winter – Great German Pilgrimage: Archbishop Siegfried I of Mainz leads a pilgrimage to Jerusalem. Either during this pilgrimage or shortly before it, the Ezzolied; a High German poem on the life of Christ, is composed.
 * Michaelsberg Abbey at Siegburg (modern Germany) is founded by Anno II, archbishop of Cologne.
 * Construction of the Piazza dei Miracoli (known as Piazza del Duomo) at Pisa in Tuscany begins.

Volcanology

 * Sunset Crater Volcano (modern-day Arizona) first erupts (approximate date)

Births

 * Adela of Flanders, queen of Denmark (approximate date)
 * Beatrice I, countess of Bigorre (approximate date)
 * Bořivoj II (or Borivoi), duke of Bohemia (approximate date)
 * Danxia Zichun, Chinese Zen Buddhist monk (d. 1117)
 * Hugh of Flavigny, French abbot (approximate date)
 * Robert Fitz Richard, English nobleman (d. 1136)

Deaths

 * August 15 – Ibn Hazm, Andalusian historian and poet (b. 994)
 * November 29 – Al-Kunduri, vizier of the Seljuk Empire (b. 1024)
 * December 19 – Fujiwara no Nagaie, Japanese nobleman (b. 1005)
 * Akkadevi, princess of the Chalukya dynasty (b. 1010)
 * Dromtön, Tibetan monk and founder of Reting Monastery
 * Dub dá Leithe (or Dubhdalethe), Irish abbot
 * Gozelo I (or Gozelon), count of Montaigu
 * Llywelyn Aurdorchog, Welsh nobleman (approximate date)
 * Yaakov ben Yakar, German Jewish rabbi (b. 990)
 * Yi Yuanji, Chinese painter (approximate date)

title: 1064


text:
1065

Year 1065 (MLXV) was a common year starting on Saturday (link will display the full calendar) of the Julian calendar.

Europe

 * December 24 – King Ferdinand I (the Great) dies in León after an 11-year reign as Emperor of All Spain. His kingdom is divided among his three sons: the eldest Sancho II, the second Alfonso VI and the youngest García II. The kingdoms of Galicia and Portugal become independent under the rule of García.

England

 * October 3 – Northumbria rebels against Tostig, who is exiled. He takes refuge with his brother-in-law, Count Baldwin V in Flanders (modern Belgium). The Northumbrian nobles choose Morcar (or Morkere) as earl at York.
 * December 28 – Westminster Abbey is consecrated by King Edward the Confessor.

Seljuk Empire

 * Alp Arslan, leader of the Seljuk Turks, campaigns against the Kipchaks and the Türkmen in Central Asia. He captures the city of Kars and plunders the western provinces of Georgia.

China

 * Sima Guang, chancellor of the Song Dynasty, heads a team of scholars in initiating the compilation of an enormous written universal history of China, known as the Zizhi Tongjian.

Religion

 * Great German Pilgrimage: A large pilgrimage led by Archbishop Siegfried I of Mainz arrives in Jerusalem after having been attacked by Bedouin bandits. Two weeks later they return to Ramla in April and take ships back to Latakia.
 * Gregory II is consecrated as catholicos of the Armenian church in Tzamandos

Astronomy

 * Guest Star: There is a “guest star” event reported in ancient Chinese records. It happened in 1065 BP, and may be related to the Strottner-Drechsler Object 20 nebula.

Births

 * Agnes of Rheinfelden, duchess of Swabia (d. 1111)
 * Callixtus II, pope of the Catholic Church (d. 1124)
 * Guarinus of Sitten, bishop of Sion (approximate date)
 * Henry I (the Long), German nobleman (d. 1087)
 * Hugh VII of Lusignan, count of La Marche (d. 1151)
 * Humbert II (the Fat), count of Savoy (d. 1103)
 * Li Jie, Chinese writer of the Song Dynasty (d. 1110)
 * Niels (or Nicholas), king of Denmark (d. 1134)
 * Richard de Montfort, French nobleman (d. 1092)
 * Robert II, count of Flanders (approximate date)
 * Sibylla of Burgundy, duchess of Burgundy (approximate date)
 * Stephen I, count palatine of Burgundy (d. 1102)
 * Vladislaus I, duke of Bohemia (approximate date)
 * Walter Tirel (or William Rufus), English nobleman

Deaths

 * February 7 – Siegfried I, count of Sponheim
 * May 17 – Egilbert (or Engelbert), bishop of Passau
 * May 18 – Frederick, duke of Lower Lorraine
 * June 27 – George the Hagiorite, Georgian calligrapher (b. 1009)
 * July 22 – Ibn Abi Hasina, Arab poet and panegyrist (b. 998)
 * July 23 – Gunther of Bamberg, German nobleman
 * December 24 – Ferdinand I (the Great), king of León and Castile
 * Diarmaid mac Tadgh Ua Ceallaigh, king of Uí Maine
 * Ermengol III (or Armengol), count of Urgell (b. 1032)
 * Gisela (or Gizella), queen consort of Hungary (b. 985)
 * Gomes Echigues, Portuguese knight and governor (b. 1010)
 * Gusiluo, Tibetan religious leader of Buddhism (b. 997)
 * Llywelyn Aurdorchog, Welsh nobleman (approximate date)
 * Thorfinn (the Mighty), Norse nobleman (approximate date)

title: 1065


text:
1067

Year 1067 (MLXVII) was a common year starting on Monday (link will display the full calendar) of the Julian calendar.

Byzantine Empire

 * May 22 – Emperor Constantine X dies after a 7-year reign at Constantinople. His wife, Empress Eudocia Macrembolitissa, is crowned Augusta and becomes co-regent for her two sons (Michael VII and Konstantios) along with Constantine's brother John Doukas, who rules as Caesar of the Byzantine Empire.

Seljuk Empire

 * Spring – The Seljuk Turks make incursions into Mesopotamia, Cilicia and Cappadocia. They sack the Byzantine city of Caesarea, move south through the Cilician Gates and raid the region around Antioch in Syria.

Europe

 * March 3 – Battle on the Nemiga River: The three sons of Grand Prince Yaroslav I (the Wise) – Iziaslav I, Sviatoslav II, and Vsevolod I – defeat the forces under Vseslav of Polotsk.
 * Eric and Eric, two pretenders to the Swedish throne, are both killed during the struggle for power in Sweden. Halsten, son of the late King Stenkil, becomes the new ruler.
 * Olaf III returns to Norway with the remaining troops from the Battle of Stamford Bridge. He is proclaimed king and co-ruler with his older brother Magnus II (Haraldsson).
 * Wartburg Castle (near Eisenach) is founded by Louis the Springer, count of Thuringia (modern Germany).
 * Minsk and Orsha are first mentioned in the chronicles, making them two of the oldest cities in Belarus.

England

 * Spring – King William I (the Conqueror) returns to Normandy and takes with him Edgar Ætheling (grandson of Edmund Ironside), Archbishop Stigand, and the brothers Morcar and Edwin.
 * Odo of Bayeux, a half-brother of William I, is appointed Earl of Kent and becomes William's deputy (or de facto regent) in England. His wealth and land become considerable.
 * Eustace II, count of Boulogne, supports the Kentishmen in an attempt to seize Dover Castle. The conspiracy fails, and Eustace is sentenced to forfeit his English fiefs.
 * Winter – William I marches on Exeter, which he besieges. The city holds out for 18 days, and after its fall William builds Rougemont Castle there to secure the region.
 * Winchester Castle in Hampshire is founded by William I; it is later one of the seats of government of the Norman kings ruling England.

China

 * January 25 – Emperor Yingzong (or Zhao Shu) of the Song dynasty dies after a 4-year reign. He is succeeded by his 18-year-old son Shen Zong as emperor of China.

Religion

 * December 6 – A fire, the second in as many years, heavily damages Canterbury Cathedral in England.

Births

 * Abu Hafs Umar an-Nasafi, Persian scholar and historian (d. 1142)
 * Adela of Normandy, countess of Blois (approximate date)
 * Ari Thorgilsson, Icelandic chronicler and writer (d. 1148)
 * John Taronites, Byzantine governor (approximate date)

Deaths

 * January 25 – Ying Zong, Chinese emperor (b. 1032)
 * February 13 – Geoffrey II, French nobleman
 * April 17 – Robert de Turlande, French priest
 * May 22 – Constantine X, Byzantine emperor (b. 1006)
 * July 12 – John Komnenos, Byzantine general
 * September 1 – Baldwin V, count of Flanders
 * November 27 – Sancha of León, queen of León
 * December 2 – Shaykh Tusi, Persian Shia scholar (b. 995)
 * Aedh Ua Con Ceanainn, king of Uí Díarmata
 * Bahmanyār, Persian philosopher and logician
 * Cai Xiang, Chinese calligrapher and poet (b. 1012)
 * Elisaveta Yaroslavna of Kiev, Norwegian queen
 * Eric and Eric, Swedish throne pretenders
 * Gervais de Château-du-Loir, French nobleman (b. 1007)
 * Muireadhach Ua Cárthaigh, Irish chief poet
 * Richard, French nobleman (House of Normandy)
 * Wulfwig (or Wulfinus), bishop of Dorchester

title: 1067


text:
1069

Byzantine Empire

 * Spring – Emperor Romanos IV begins a campaign against the Seljuk Turks, and marches towards the Euphrates via Melitene. He crosses the river at Romanopolis (modern Turkey), and captures the strategic fortress city of Chliat on the north-western shore of Lake Van. Romanos leaves a Byzantine rear guard on the upper Euphrates under General Philaretos Brachamios with orders to defend the Mesopotamian frontier.
 * Seljuk forces under Alp Arslan defeat the Byzantine rear guard and advance deep into Cappadocia and Lycaonia. They plunder at will, but fail to capture the city of Iconium. Romanos retreats and returns to Constantinople. Alp Arslan takes advantage of Romanos' retreat and captures Manzikert. He recaptures the strategical fortress cities of Chliat and Van, consolidating his control over the Lake Van region.

Europe

 * Spring – Romanos IV sends a Byzantine fleet (supported with an army) to relieve the siege of Bari. The Normans under Robert Guiscard defeat the Byzantines, and occupy the cities of Gravina and Obbiano in Apulia.
 * February 28 – King Abbad II al-Mu'tadid dies after a 27-year reign. He is succeeded by his son Al-Mu'tamid ibn Abbad, who becomes the ruler of the Taifa of Seville in Al-Andalus (until 1091).

England

 * January 28 – Northumbrians kill the new Norman earl of Northumbria, Robert de Comines, at Durham, and attack York.
 * King Sweyn II of Denmark lands a fleet in the Humber in support of the Northumbrian rebels and they join him to burn York, attacking its two castles and destroying the old Minster.
 * At Stafford, William the Conqueror swiftly defeats a rebellion led by Edwin, Earl of Mercia.
 * Winter of 1069–1070 – Harrying of the North: King William the Conqueror quells rebellions made by his English subjects against his rule, campaigning through the north of England with his forces, burning houses, crops, cattle and land from York to Durham, resulting in the deaths of over 100,000 people, mainly from starvation and winter cold.

Asia

 * Emperor Shenzong of Song China appoints Wang Anshi as his chief chancellor. He implements the New Policies, which include financial and trade reforms, defense and order, institution of the baojia system, etc.
 * Nam tiến, the southward expansion of the territory of Đại Việt (modern Vietnam), begins when a Lý dynasty army attacks Champa, capturing King Rudravarman III.

Births

 * Anseau of Garlande, French nobleman (d. 1118)
 * Kamakura Gongorō Kagemasa, Japanese samurai
 * Leo Diogenes, Byzantine co-emperor (d. 1087)
 * Approximate date
 * Mieszko Bolesławowic, Polish prince (d.1089)
 * Diego Gelmírez, Galician archbishop

Deaths

 * January 28 – Robert de Comines, English nobleman
 * February 28 – Abbad II al-Mu'tadid, Abbadid king
 * April 28 – Magnus II (Haraldsson), king of Norway
 * August 15 – Ibn Hazm, Moorish historian (b. 994)
 * September 11 – Ealdred, archbishop of York
 * December 24 – Dedi II (the Younger), margrave of Lower Lusatia (b. c.997)
 * Godfrey III (the Bearded), duke of Lower Lorraine
 * Gytha Thorkelsdóttir, Danish noblewoman (b. 997)
 * Pedro Seguin (or Seguini), bishop of Ourense
 * Tilopa, Indian tantric practitioner (b. 988)
 * Approximate date – Rhiwallon ap Cynfyn, Welsh king (b. c.1020)

title: 1069


text:
1074

Year 1074 (MLXXIV) was a common year starting on Wednesday (link will display the full calendar) of the Julian calendar.

Byzantine Empire

 * Spring – Norman mercenaries, led by Roussel de Bailleul, proclaim John Doukas emperor of the Byzantine Empire. His nephew, Emperor Michael VII (Doukas), forms an alliance with Seljuk chieftain Suleiman ibn Qutulmish, who is raiding in the eastern regions of Anatolia. The Seljuk Turks ambush the Norman forces; Roussel and John are defeated and captured. But a ransom, raised by Roussel's wife, allows him to return to Amaseia.

Europe

 * February 2 – Treaty of Gerstungen: Emperor Henry IV is forced to restore the peace with Duke Otto of Nordheim (one of the Saxon leaders of the Saxon Rebellion). He signs a treaty in Gerstungen Castle, on the River Werra in Thuringia (modern Germany).
 * February 7 – Battle of Montesarchio: Prince Pandulf IV, co-ruler of Benevento, is killed while fighting the Normans in southern Italy.
 * March 14 – Battle of Mogyoród: King Solomon is defeated by his cousins, Duke Géza I and Ladislaus I. He is dethroned and Géza becomes the new ruler of Hungary.
 * October 21 – The Belgium beer brand Affligem is founded.

Africa

 * Spring – Badr al-Jamali becomes Chief Wazir (Grand Vizier) and effectively military dictator of the Fatimid Caliphate under Caliph Al-Mustansir Billah in Egypt.

China

 * Emperor Shen Zong of the Song Dynasty establishes a Marine Office and a Goods Control Bureau north-west of Shanghai, allowing for the loading and unloading of freight.

Religion

 * Pope Gregory VII temporarily excommunicates the Norman nobleman Robert Guiscard.

Births

 * February 12 – Conrad II, king of Germany (d. 1101)
 * September 16 – Al-Musta'li, Fatimid caliph (d. 1101)
 * Abu Mansur Mauhub al-Jawaliqi, Arab philologist (d. 1144)
 * Edgar (the Valliant), king of Scotland (d. 1107)
 * Hugh I, count of Champagne (approximate date)
 * Ibn al-Tilmidh, Syriac physician and poet (d. 1165)
 * Maud, queen of Scotland (approximate date)

Deaths

 * February 7 – Pandulf IV, Lombard prince
 * April 25 – Herman I, margrave of Baden
 * May 6 – Dúnán (or Donat), bishop of Dublin
 * October 25 – Shōshi, empress of Japan (b. 988)
 * Ibn al-Wafid, Andalusian pharmacologist
 * Joseph Tarchaneiotes, Byzantine general
 * Peter Krešimir IV, king of Croatia (or 1075)
 * Ralph IV (or Raoul), French nobleman
 * Wugunai, Chinese chieftain (b. 1021)
 * Yang Wenguang, Chinese general

title: 1074


text:
1075

Year 1075 (MLXXV) was a common year starting on Thursday (link will display the full calendar) of the Julian calendar.

Africa

 * The Kingdom of Mapungubwe is established, in modern-day South Africa.

Byzantine Empire

 * The future Emperor Alexios Komnenos captures the Norman rebel Roussel de Bailleul in Amaseia. Roussel had established a principality in eastern Anatolia in 1073 after rebelling against Emperor Michael VII Doukas, basing his power on his western mercenaries and local support in exchange for protection against invading Turkmen.

Europe

 * June 9 – First Battle of Langensalza: Emperor Henry IV defeats the Saxon nobles on the River Unstrut near Langensalza in Thuringia (modern Germany). He subjugates Saxony, and immediately tries to reassert his rights as the sovereign of northern Italy.
 * Anund Gårdske is deposed as king of Svealand (also called Sweden proper). King Håkan the Red of Götaland proclaims himself ruler of all Sweden.

England

 * Revolt of the Earls: The Earls Ralph de Gael, Roger de Breteuil and Waltheof, begin a revolt against King William I (the Conqueror) in the last serious act of resistance to the Norman Conquest.
 * Roger de Breteuil is brought before the Great Council. He is deprived of his lands and sentenced to perpetual imprisonment. Ralph de Gael and Waltheof are charged as co-conspirators.
 * August 25 – Council of London: Archbishop Lanfranc instigates the movement of English bishoprics. One of these is the bishopric of Sherborne and Wilton which is moved to Old Sarum.

Asia

 * Summer – Shen Kuo, Chinese polymath scientist and statesman, solves a border dispute with the Liao Dynasty by dredging up old diplomatic records. He refutes Emperor Dao Zong's bluffs point for point during a meeting at Mt. Yongan (near modern-day Pingquan), reestablishing the rightful borders of the Song Dynasty.
 * Vietnamese forces under General Lý Thường Kiệt defend Vietnam against a Chinese invasion.
 * The Liao Dynasty version of the Buddhist Tripiṭaka is completed (approximate date).

Religion

 * February – Pope Gregory VII holds a council in the Lateran Palace at Rome. He publishes a decree against laymen investiture (an act which will later cause the Investiture Controversy).
 * April – The Dictatus papae (a compilation of 27 statements of powers) are included in the registry of Gregory VII, in which he asserts papal authority over earthly as well as spiritual rulers.
 * December 8 – Gregory VII writes a letter of reprimand to Henry IV. He accuses him of breaching his word and continued support of excommunicated councilors.
 * December 25 – Gregory VII is kidnapped in the church during Christmas night in Rome and briefly imprisoned by the Roman nobleman Cencio I Frangipane.

Births

 * March 18 – Al-Zamakhshari, Persian philosopher (d. 1144)
 * April 16 – Orderic Vitalis, English Benedictine chronicler
 * June 5 – Tianzuo (Yanning), last emperor of the Liao dynasty
 * November 25 – Taizong, emperor of the Jin dynasty (d. 1135)
 * Adelaide del Vasto, countess and regent of Sicily (d. 1118)
 * Bertha, queen of Aragon and Navarre (approximate date)
 * Conrad I, archbishop of Salzburg (approximate date)
 * Frederick I, archbishop of Cologne (approximate date)
 * Gerald de Windsor, English nobleman (approximate date) (d. 1135)
 * Kim Bu-sik, Korean statesman and general (d. 1151)
 * Gisela of Burgundy, Marchioness of Montferrat, French noblewoman (d. 1135)
 * Henry IX "the Black", duke of Bavaria (d. 1126)
 * Jaya Pala, Indian king of Kamarupa (d. 1100)
 * Jinadattasuri, Indian Jain poet and writer (d. 1154)
 * Lothair III (or II) of Supplinburg, Holy Roman Emperor (d. 1137)
 * Nicholas the Pilgrim, Italian shepherd and saint (d. 1094)
 * Norbert of Xanten, archbishop of Magdeburg (d. 1134)
 * Raymond Pilet d'Alès, French nobleman (d. 1120)
 * Soběslav I (Sobeslaus), duke of Bohemia (d. 1140)
 * Svatopluk "the Lion" of Olomouc, duke of Bohemia (d. 1109)
 * Tancred, Italo-Norman leader of the First Crusade (d. 1112)

Deaths

 * March 29 – Ottokar I (or Otakar), German nobleman
 * April 2 – Al-Qa'im, Abbasid caliph in Baghdad (b. 1001)
 * April 15 – Erlembald Cotta, Italian military leader
 * May 21 – Richeza (or Adelaide), Hungarian queen
 * June 9 – Gebhard of Supplinburg, German nobleman
 * June 10 – Ernest (the Brave), margrave of Austria (b. 1027)
 * June 23 – Theodwin, prince-bishop of Liège
 * August 2 – John VIII, patriarch of Constantinople
 * August 27 – Minamoto no Yoriyoshi, Japanese nobleman (b. 988)
 * November 6 – Fujiwara no Norimichi, Japanese nobleman (b. 996)
 * December 4 – Anno II, archbishop of Cologne
 * December 13 – Xiao Guanyin, Chinese empress (b. 1040)
 * December 18 – Edith of Wessex, English queen
 * Alī ibn Ahmad al-Nasawī, Persian mathematician
 * Al-Mamun, Andalusian emir of the Taifa of Toledo
 * Amhalgaidh mac Cathal, king of Maigh Seóla
 * Anne of Kiev (or Agnes), French queen and regent
 * Dedi I (or Dedo), margrave of the Saxon Ostmark
 * Domnall mac Murchada, king of Leinster and Dublin
 * Frederick II, German nobleman and overlord (b. 1005)
 * Gofraid mac Amlaíb meic Ragnaill, king of Dublin
 * Gundekar II (or Gunzo), bishop of Eichstätt (b. 1019)
 * Ibn Butlan, Arab Nestorian Christian physician (b. 1038)
 * Ibn Hayyan, Moorish historian and writer (b. 987)
 * John Xiphilinus, Byzantine historian (approximate date)
 * Peter Krešimir IV (the Great), king of Croatia (or 1074)
 * Rashid al-Dawla Mahmud, Mirdasid emir of Aleppo
 * Siward (or Sigweard), bishop of Rochester

title: 1075


text:
1076

Year 1076 (MLXXVI) was a leap year starting on Friday (link will display the full calendar) of the Julian calendar.

Europe

 * January 24 – Synod of Worms: Emperor Henry IV, Holy Roman Emperor, holds a synod in Worms (modern Germany). The assembly declares Pope Gregory VII deposed, and the bishops abandon their allegiance to him.
 * February 22 – Gregory VII pronounces a sentence of excommunication against Henry IV at Rome. He is excluded from the Catholic Church, and all the bishops named by Henry are excommunicated.
 * Summer – Dirk V, count of Holland, re-conquers West Frisia (modern Netherlands) from the Archdiocese of Utrecht. He besieges Bishop Conrad at the castle of IJsselmonde, taking him prisoner.
 * October 8 – Demetrius Zvonimir is crowned as king of Croatia in Solin (near Split), in the Basilica of Saint Peter and Moses (known later as the Hollow Church) by a representative of Gregory VII.
 * December 13 – Norman conquest of southern Italy: Italo-Norman forces under Robert Guiscard de Hauteville and Richard I of Capua, conquer the fortress city of Salerno after a short siege.
 * December 26 – Bolesław II the Bold (or "the Generous") is crowned as King of Poland by Archbishop Bogumił in Gniezno Cathedral. Bolesław supports Gregory VII in his conflict against Henry IV.

England

 * May 31 – Waltheof, Earl of Northumbria, a participant in the Revolt of the Earls against King William the Conqueror, is beheaded near Winchester.
 * Approximate date – The Trial of Penenden Heath is held, with an important ruling regarding land rights subsequent to the Norman Conquest.
 * November 1 – A frost begins that lasts until April 1077.

Africa

 * Koumbi Saleh, an important mercantile and political center of the Ghana Empire (modern Mauritania), is besieged by the Almoravids (approximate date).

Asia

 * Vikramaditya VI deposes his older brother Someshvara II to become king of the Western Chalukya Empire (modern India).

Literature

 * Anselm of Aosta, an Italian Benedictine abbot, completes his Monologion at the request of his fellow monks.

Religion

 * Demetrius Zvonimir donates the Benedictine monastery of St. Gregory in Vrana to Gregory VII.

Births

 * June 1 – Mstislav I (the Great), Grand Prince of Kiev (d. 1132)
 * Abu Bakr ibn al-Arabi, Moorish scholar and judge (d. 1148)
 * Fujiwara no Sadazane, Japanese calligrapher (d. 1120)
 * Hualani, Hawaiian queen and regent (approximate date)
 * Urban (or Gwrgan), bishop of Llandaff (d. 1134)

Deaths

 * March 18 – Ermengarde of Anjou, duchess of Burgundy
 * March 21 – Robert I (the Old), duke of Burgundy (b. 1011)
 * April 18 – Beatrice of Bar, French duchess and regent
 * April 28 – Sweyn II (Estridsson), king of Denmark
 * May 8 – Nasr ibn Mahmud, Mirdasid emir of Aleppo
 * May 26 – Ramon Berenguer I, count of Barcelona (b. 1023)
 * May 31 – Waltheof, earl of Northumbria (executed)
 * June 4 – Sancho IV, king of Pamplona (or Navarre)
 * July 15 – Arnost (or Arnošt), bishop of Rochester
 * Godfrey IV (the Hunchback), duke of Lower Lorraine
 * Ramihrdus of Cambrai, French priest and martyr (or 1077)
 * William Busac, English nobleman (jure uxoris) (b. 1020)

title: 1076