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Grammatical aspect

In linguistics, aspect is a grammatical category that expresses how a verbal action, event, or state, extends over time. For instance, perfective aspect is used in referring to an event conceived as bounded and unitary, without reference to any flow of time during the event ("I helped him"). Imperfective aspect is used for situations conceived as existing continuously or habitually as time flows ("I was helping him"; "I used to help people").

Further distinctions can be made, for example, to distinguish states and ongoing actions (continuous and progressive aspects) from repetitive actions (habitual aspect).

Certain aspectual distinctions express a relation between the time of the event and the time of reference. This is the case with the perfect aspect, which indicates that an event occurred prior to (but has continuing relevance at) the time of reference: "I have eaten"; "I had eaten"; "I will have eaten".

Different languages make different grammatical aspectual distinctions; some (such as Standard German; see below) do not make any. The marking of aspect is often conflated with the marking of tense and mood (see tense–aspect–mood). Aspectual distinctions may be restricted to certain tenses: in Latin and the Romance languages, for example, the perfective–imperfective distinction is marked in the past tense, by the division between preterites and imperfects. Explicit consideration of aspect as a category first arose out of study of the Slavic languages; here verbs often occur in pairs, with two related verbs being used respectively for imperfective and perfective meanings.

The concept of grammatical aspect (or verbal aspect) should not be confused with perfect and imperfect verb forms; the meanings of the latter terms are somewhat different, and in some languages, the common names used for verb forms may not follow the actual aspects precisely.

History
The Indian linguist Yaska (c. 7th century BCE) dealt with grammatical aspect, distinguishing actions that are processes (bhāva), from those where the action is considered as a completed whole (mūrta). This is the key distinction between the imperfective and perfective. Yaska also applied this distinction to a verb versus an action nominal.

Grammarians of the Greek and Latin languages also showed an interest in aspect, but the idea did not enter into the modern Western grammatical tradition until the 19th century via the study of the grammar of the Slavic languages. The earliest use of the term recorded in the Oxford English Dictionary dates from 1853.

Modern usage
Aspect is often confused with the closely related concept of tense, because they both convey information about time. While tense relates the time of referent to some other time, commonly the speech event, aspect conveys other temporal information, such as duration, completion, or frequency, as it relates to the time of action. Thus tense refers to temporally when while aspect refers to temporally how. Aspect can be said to describe the texture of the time in which a situation occurs, such as a single point of time, a continuous range of time, a sequence of discrete points in time, etc., whereas tense indicates its location in time.

For example, consider the following sentences: "I eat", "I am eating", "I have eaten", and "I have been eating". All are in the present tense, indicated by the present-tense verb of each sentence (eat, am, and have). Yet since they differ in aspect each conveys different information or points of view as to how the action pertains to the present.

Grammatical aspect is a formal property of a language, distinguished through overt inflection, derivational affixes, or independent words that serve as grammatically required markers of those aspects. For example, the Kʼicheʼ language spoken in Guatemala has the inflectional prefixes k- and x- to mark incompletive and completive aspect; Mandarin Chinese has the aspect markers -le 了, -zhe 着, zài- 在, and -guò 过 to mark the perfective, durative stative, durative progressive, and experiential aspects, and also marks aspect with adverbs; and English marks the continuous aspect with the verb to be coupled with present participle and the perfect with the verb to have coupled with past participle. Even languages that do not mark aspect morphologically or through auxiliary verbs, however, can convey such distinctions by the use of adverbs or other syntactic constructions.

Grammatical aspect is distinguished from lexical aspect or Aktionsart, which is an inherent feature of verbs or verb phrases and is determined by the nature of the situation that the verb describes.

Common aspectual distinctions
The most fundamental aspectual distinction, represented in many languages, is between perfective aspect and imperfective aspect. This is the basic aspectual distinction in the Slavic languages.

It semantically corresponds to the distinction between the morphological forms known respectively as the aorist and imperfect in Greek, the preterite and imperfect in Spanish, the simple past (passé simple) and imperfect in French, and the perfect and imperfect in Latin (from the Latin perfectus, meaning "completed").

Essentially, the perfective aspect looks at an event as a complete action, while the imperfective aspect views an event as the process of unfolding or a repeated or habitual event (thus corresponding to the progressive/continuous aspect for events of short-term duration and to habitual aspect for longer terms).

For events of short durations in the past, the distinction often coincides with the distinction in the English language between the simple past "X-ed," as compared to the progressive "was X-ing". Compare "I wrote the letters this morning" (i.e. finished writing the letters: an action completed) and "I was writing the letters this morning" (the letters may still be unfinished).

In describing longer time periods, English needs context to maintain the distinction between the habitual ("I called him often in the past" – a habit that has no point of completion) and perfective ("I called him once" – an action completed), although the construct "used to" marks both habitual aspect and past tense and can be used if the aspectual distinction otherwise is not clear.

Sometimes, English has a lexical distinction where other languages may use the distinction in grammatical aspect. For example, the English verbs "to know" (the state of knowing) and "to find out" (knowing viewed as a "completed action") correspond to the imperfect and perfect forms of the equivalent verbs in French and Spanish, savoir and saber. This is also true when the sense of verb "to know" is "to know somebody", in this case opposed in aspect to the verb "to meet" (or even to the construction "to get to know"). These correspond to imperfect and perfect forms of conocer in Spanish, and connaître in French. In German, on the other hand, the distinction is also lexical (as in English) through verbs kennen and kennenlernen, although the semantic relation between both forms is much more straightforward since kennen means "to know" and lernen means "to learn".

Aspect vs. tense
The Germanic languages combine the concept of aspect with the concept of tense. Although English largely separates tense and aspect formally, its aspects (neutral, progressive, perfect, progressive perfect, and [in the past tense] habitual) do not correspond very closely to the distinction of perfective vs. imperfective that is found in most languages with aspect. Furthermore, the separation of tense and aspect in English is not maintained rigidly. One instance of this is the alternation, in some forms of English, between sentences such as "Have you eaten?" and "Did you eat?".

In European languages, rather than locating an event time, the way tense does, aspect describes "the internal temporal constituency of a situation", or in other words, aspect is a way "of conceiving the flow of the process itself". English aspectual distinctions in the past tense include "I went, I used to go, I was going, I had gone"; in the present tense "I lose, I am losing, I have lost, I have been losing, I am going to lose"; and with the future modal "I will see, I will be seeing, I will have seen, I am going to see". What distinguishes these aspects within each tense is not (necessarily) when the event occurs, but how the time in which it occurs is viewed: as complete, ongoing, consequential, planned, etc.

In most dialects of Ancient Greek, aspect is indicated uniquely by verbal morphology. For example, the very frequently used aorist, though a functional preterite in the indicative mood, conveys historic or 'immediate' aspect in the subjunctive and optative. The perfect in all moods is used as an aspectual marker, conveying the sense of a resultant state. E.g. ὁράω – I see (present); εἶδον – I saw (aorist); οἶδα – I am in a state of having seen = I know (perfect). Turkish has a same/similar aspect, such as in Görmüş bulunuyorum/durumdayım, where görmüş means "having seen" and bulunuyorum/durumdayım means "I am in the state".

In many Sino-Tibetan languages, such as Mandarin, verbs lack grammatical markers of tense, but are rich in aspect (Heine, Kuteva 2010, p. 10). Markers of aspect are attached to verbs to indicate aspect. Event time is inferred through use of these aspectual markers, along with optional inclusion of adverbs.

Lexical vs. grammatical aspect
There is a distinction between grammatical aspect, as described here, and lexical aspect. Other terms for the contrast lexical vs. grammatical include: situation vs. viewpoint and inner vs. outer. Lexical aspect, also known as Aktionsart, is an inherent property of a verb or verb-complement phrase, and is not marked formally. The distinctions made as part of lexical aspect are different from those of grammatical aspect. Typical distinctions are between states ("I owned"), activities ("I shopped"), accomplishments ("I painted a picture"), achievements ("I bought"), and punctual, or semelfactive, events ("I sneezed"). These distinctions are often relevant syntactically. For example, states and activities, but not usually achievements, can be used in English with a prepositional for-phrase describing a time duration: "I had a car for five hours", "I shopped for five hours", but not "*I bought a car for five hours". Lexical aspect is sometimes called Aktionsart, especially by German and Slavic linguists. Lexical or situation aspect is marked in Athabaskan languages.

One of the factors in situation aspect is telicity. Telicity might be considered a kind of lexical aspect, except that it is typically not a property of a verb in isolation, but rather a property of an entire verb phrase. Achievements, accomplishments and semelfactives have telic situation aspect, while states and activities have atelic situation aspect.

The other factor in situation aspect is duration, which is also a property of a verb phrase. Accomplishments, states, and activities have duration, while achievements and semelfactives do not.

Indicating aspect
In some languages, aspect and time are very clearly separated, making them much more distinct to their speakers. There are a number of languages that mark aspect much more saliently than time. Prominent in this category are Chinese and American Sign Language, which both differentiate many aspects but rely exclusively on optional time-indicating terms to pinpoint an action with respect to time. In other language groups, for example in most modern Indo-European languages (except Slavic languages and some Indo-Aryan languages like Hindi ), aspect has become almost entirely conflated, in the verbal morphological system, with time.

In Russian, aspect is more salient than tense in narrative. Russian, like other Slavic languages, uses different lexical entries for the different aspects, whereas other languages mark them morphologically, and still others with auxiliaries (e.g., English).

In Hindi, the aspect marker is overtly separated from the tense/mood marker. Periphrastic Hindi verb forms consist of two elements. The first of these two elements is the aspect marker and the second element (the copula) is the common tense/mood marker.

In literary Arabic (الْفُصْحَى al-fuṣḥā) the verb has two aspect-tenses: perfective (past), and imperfective (non-past). There is some disagreement among grammarians whether to view the distinction as a distinction in aspect, or tense, or both. The past verb (الْفِعْل الْمَاضِي al-fiʿl al-māḍī) denotes an event (حَدَث ḥadaṯ) completed in the past, but it says nothing about the relation of this past event to present status. For example, وَصَلَ waṣala, "arrived", indicates that arrival occurred in the past without saying anything about the present status of the arriver – maybe they stuck around, maybe they turned around and left, etc. – nor about the aspect of the past event except insofar as completeness can be considered aspectual. This past verb is clearly similar if not identical to the Greek aorist, which is considered a tense but is more of an aspect marker. In the Arabic, aorist aspect is the logical consequence of past tense. By contrast, the "Verb of Similarity" (الْفِعْل الْمُضَارِع al-fiʿl al-muḍāriʿ), so called because of its resemblance to the active participial noun, is considered to denote an event in the present or future without committing to a specific aspectual sense beyond the incompleteness implied by the tense: يَضْرِبُ (yaḍribu, he strikes/is striking/will strike/etc.). Those are the only two "tenses" in Arabic (not counting أَمْر amr, command or imperative, which is traditionally considered as denoting future events.) To explicitly mark aspect, Arabic uses a variety of lexical and syntactic devices.

Contemporary Arabic dialects are another matter. One major change from al-fuṣḥā is the use of a prefix particle (بِ bi in Egyptian and Levantine dialects—though it may have a slightly different range of functions in each dialect) to explicitly mark progressive, continuous, or habitual aspect: بيكتب, bi-yiktib, he is now writing, writes all the time, etc.

Aspect can mark the stage of an action. The prospective aspect is a combination of tense and aspect that indicates the action is in preparation to take place. The inceptive aspect identifies the beginning stage of an action (e.g. Esperanto uses ek-, e.g. Mi ekmanĝas, "I am beginning to eat".) and inchoative and ingressive aspects identify a change of state (The flowers started blooming) or the start of an action (He started running). Aspects of stage continue through progressive, pausative, resumptive, cessive, and terminative.

Important qualifications:

 * Although the perfective is often thought of as representing a "momentary action", this is not strictly correct. It can equally well be used for an action that took time, as long as it is conceived of as a unit, with a clearly defined start and end, such as "Last summer I visited France".
 * Grammatical aspect represents a formal distinction encoded in the grammar of a language. Although languages that are described as having imperfective and perfective aspects agree in most cases in their use of these aspects, they may not agree in every situation. For example:
 * Some languages have additional grammatical aspects. Spanish and Ancient Greek, for example, have a perfect (not the same as the perfective), which refers to a state resulting from a previous action (also described as a previous action with relevance to a particular time, or a previous action viewed from the perspective of a later time). This corresponds (roughly) to the "have X-ed" construction in English, as in "I have recently eaten". Languages that lack this aspect (such as Portuguese, which is closely related to Spanish) often use the past perfective to render the present perfect (compare the roughly synonymous English sentences "Have you eaten yet?" and "Did you eat yet?").
 * In some languages, the formal representation of aspect is optional, and can be omitted when the aspect is clear from context or does not need to be emphasized. This is the case, for example, in Mandarin Chinese, with the perfective suffix le and (especially) the imperfective zhe.
 * For some verbs in some languages, the difference between perfective and imperfective conveys an additional meaning difference; in such cases, the two aspects are typically translated using separate verbs in English. In Greek, for example, the imperfective sometimes adds the notion of "try to do something" (the so-called conative imperfect); hence, the same verb, in the imperfective (present or imperfect) and aorist, respectively, is used to convey look and see, search and find, listen and hear. (For example, ἠκούομεν (ēkouomen, "we listened") vs. ἠκούσαμεν (ēkousamen, "we heard").) Spanish has similar pairs for certain verbs, such as (imperfect and preterite, respectively) sabía ("I knew") vs. supe ("I found out"), podía ("I was able to") vs. pude ("I succeeded (in doing something)"), quería ("I wanted to") vs. quise ("I tried to"), and no quería ("I did not want to") vs. no quise ("I refused (to do something)"). Such differences are often highly language-specific.

English
The English tense–aspect system has two morphologically distinct tenses, past and non-past, the latter of which is also known as the present-future or, more commonly and less formally, simply the present. No marker of a distinct future tense exists on the verb in English; the futurity of an event may be expressed through the use of the auxiliary verbs "will" and "shall", by a non-past form plus an adverb, as in "tomorrow we go to New York City", or by some other means. Past is distinguished from non-past, in contrast, with internal modifications of the verb. These two tenses may be modified further for progressive aspect (also called continuous aspect), for the perfect, or for both. These two aspectual forms are also referred to as BE +ING and HAVE +EN, respectively, which avoids what may be unfamiliar terminology.

Aspects of the present tense: (While many elementary discussions of English grammar classify the present perfect as a past tense, it relates the action to the present time. One cannot say of someone now deceased that they "have eaten" or "have been eating". The present auxiliary implies that they are in some way present (alive), even when the action denoted is completed (perfect) or partially completed (progressive perfect).)
 * Present simple (not progressive, not perfect): "I eat"
 * Present progressive (progressive, not perfect): "I am eating"
 * Present perfect (not progressive, perfect): "I have eaten"
 * Present perfect progressive (progressive, perfect): "I have been eating"

Aspects of the past tense:
 * Past simple (not progressive, not perfect): "I ate"
 * Past progressive (progressive, not perfect): "I was eating"
 * Past perfect (not progressive, perfect): "I had eaten"
 * Past perfect progressive (progressive, perfect): "I had been eating"

Aspects can also be marked on non-finite forms of the verb: "(to) be eating" (infinitive with progressive aspect), "(to) have eaten" (infinitive with perfect aspect), "having eaten" (present participle or gerund with perfect aspect), etc. The perfect infinitive can further be governed by modal verbs to express various meanings, mostly combining modality with past reference: "I should have eaten" etc. In particular, the modals will and shall and their subjunctive forms would and should are used to combine future or hypothetical reference with aspectual meaning:
 * Simple future, simple conditional: "I will eat", "I would eat"
 * Future progressive, conditional progressive: "I will be eating", "I would be eating"
 * Future perfect, conditional perfect: "I will have eaten", "I would have eaten"
 * Future perfect progressive, conditional perfect progressive: "I will have been eating", "I would have been eating"

The uses of the progressive and perfect aspects are quite complex. They may refer to the viewpoint of the speaker:

 * I was walking down the road when I met Michael Jackson's lawyer. (Speaker viewpoint in middle of action)
 * I have traveled widely, but I have never been to Moscow. (Speaker viewpoint at end of action)

But they can have other illocutionary forces or additional modal components:

 * You are being stupid now. (You are doing it deliberately)
 * You are not having chocolate with your sausages! (I forbid it)
 * I am having lunch with Mike tomorrow. (It is decided)

English expresses some other aspectual distinctions with other constructions. Used to + VERB is a past habitual, as in "I used to go to school," and going to / gonna + VERB is a prospective, a future situation highlighting current intention or expectation, as in "I'm going to go to school next year."

African American Vernacular English
The aspectual systems of certain dialects of English, such as African-American Vernacular English (see for example habitual be), and of creoles based on English vocabulary, such as Hawaiian Creole English, are quite different from those of standard English, and often reflect a more elaborate paradigm of aspectual distinctions (often at the expense of tense). The following table, appearing originally in Green (2002) shows the possible aspectual distinctions in AAVE in their prototypical, negative and stressed/emphatic affirmative forms:

German vernacular and colloquial
Although Standard German does not have aspects, many Upper German and all West Central German dialects, and some more vernacular forms of German do make an aspectual distinction which partly corresponds with the English continuous form: alongside the standard present tense Ich esse ('I eat') and past Ich aß ('I ate') there is the form Ich bin/war am essen/Essen ('I am/was at the eating'; capitalization varies). This is formed by the conjugated auxiliary verb sein ("to be") followed by the preposition and article am (=an dem) and the infinitive, which German uses in many constructions as a verbal noun.

In the Tyrolean and other Bavarian regiolect the prefix *da can be found, which form perfective aspects. "I hu's gleant" (Ich habe es gelernt = I learnt it) vs. "I hu's daleant" (*Ich habe es DAlernt = I succeeded in learning).

Dutch
In Dutch (a West Germanic language), two types of continuous form are used. Both types are considered Standard Dutch.

The first type is very similar to the non-standard German type. It is formed by the conjugated auxiliary verb zijn ("to be"), followed by aan het and the gerund (which in Dutch matches the infinitive). For example:

 * Present progressive: Ik ben aan het werken ("I am working")
 * Past progressive: Ik was aan het werken ("I was working")
 * Future progressive: Ik zal aan het werken zijn ("I will be working")

The second type is formed by one of the conjugated auxiliary verbs liggen ("to lie"), zitten ("to sit"), hangen ("to hang"), staan ("to stand") or lopen ("to walk"), followed by the preposition te and the infinitive. The conjugated verbs indicate the stance of the subject performing or undergoing the action.

 * Present progressive: Ik zit te eten ("I am eating [while sitting]"), De was hangt te drogen ("The laundry is drying [while hanging]")
 * Past progressive: Ik lag te lezen ("I was reading [while lying]"), Ik stond te kijken ("I was watching [while standing]")
 * Future progressive: Ik zal zitten te werken ("I will be working [while sitting]")

Sometimes the meaning of the auxiliary verb is diminished to 'being engaged in'. Take for instance these examples:

 * De leraar zit steeds te zeggen dat we moeten luisteren ("The teacher keeps telling us to listen")
 * Iedereen loopt te beweren dat het goed was ("Everyone keeps on saying that it was good")
 * Zit niet zo te zeuren ("Stop whining")

In these cases, there is generally an undertone of irritation.

Slavic languages
The Slavic languages make a clear distinction between perfective and imperfective aspects; it was in relation to these languages that the modern concept of aspect originally developed.

In Slavic languages, a given verb is, in itself, either perfective or imperfective. Consequently, each language contains many pairs of verbs, corresponding to each other in meaning, except that one expresses perfective aspect and the other imperfective. (This may be considered a form of lexical aspect.) Perfective verbs are commonly formed from imperfective ones by the addition of a prefix, or else the imperfective verb is formed from the perfective one by modification of the stem or ending. Suppletion also plays a small role. Perfective verbs cannot generally be used with the meaning of a present tense – their present-tense forms in fact have future reference. An example of such a pair of verbs, from Polish, is given below:
 * Infinitive (and dictionary form): pisać ("to write", imperfective); napisać ("to write", perfective)
 * Present/simple future tense: pisze ("writes"); napisze ("will write", perfective)
 * Compound future tense (imperfective only): będzie pisać ("will write, will be writing")
 * Past tense: pisał ("was writing, used to write, wrote", imperfective); napisał ("wrote", perfective)

In at least the East Slavic and West Slavic languages, there is a three-way aspect differentiation for verbs of motion with the determinate imperfective, indeterminate imperfective, and perfective. The two forms of imperfective can be used in all three tenses (past, present, and future), but the perfective can only be used with past and future. The indeterminate imperfective expresses habitual aspect (or motion in no single direction), while the determinate imperfective expresses progressive aspect. The difference corresponds closely to that between the English "I (regularly) go to school" and "I am going to school (now)". The three-way difference is given below for the Russian basic (unprefixed) verbs of motion.

When prefixes are attached to Russian verbs of motion they become more or less normal imperfective/perfective pairs, with the indeterminate imperfective becoming the prefixed imperfective and the determinate imperfective becoming the prefixed perfective. For example, prefix при- pri- + indeterminate ходи́ть khodít = приходи́ть prikhodít (to arrive (on foot), impf.); and prefix при- pri- + determinate идти́ idtí = прийти prijtí (to arrive (on foot), pf.).

Romance languages
Modern Romance languages merge the concepts of aspect and tense but consistently distinguish perfective and imperfective aspects in the past tense. This derives directly from the way the Latin language used to render both aspects and consecutio temporum.

Italian
Italian language example using the verb mangiare ("to eat"): The imperfetto/trapassato prossimo contrasts with the passato remoto/trapassato remoto in that imperfetto renders an imperfective (continuous) past while passato remoto expresses an aorist (punctual/historical) past.

Other aspects in Italian are rendered with other periphrases, like prospective (io sto per mangiare "I'm about to eat", io starò per mangiare "I shall be about to eat"), or continuous/progressive (io sto mangiando "I'm eating", io starò mangiando "I shall be eating").

Hindi
Hindi has three aspects, habitual aspect, perfective aspect and the progressive aspect. Each of these three aspects are formed from their participles. The aspects of Hindi when conjugated into their personal forms can be put into five grammatical moods: indicative, presumptive, subjunctive, contrafactual, and imperative. In Hindi, the aspect marker is overtly separated from the tense/mood marker. Periphrastic Hindi verb forms consist of two elements. The first of these two elements is the aspect marker. The second element (the copula) is the common tense/mood marker.

There are a couple of verbs which can be used as the copula to the aspectual participles: होना (honā) [to be, happen], रहना (rêhnā) [to stay, remain], आना (ānā) [to come], and जाना (jānā) [to go]. Each of these copulas provide a unique nuance to the aspect. The default (unmarked) copula is होना (honā) [to be]. These copulas can themselves be conjugated into an aspectual participle and used with another copula, hence forming subaspects. (Seeː Hindi verbs)

Finnic languages
Finnish and Estonian, among others, have a grammatical aspect contrast of telicity between telic and atelic. Telic sentences signal that the intended goal of an action is achieved. Atelic sentences do not signal whether any such goal has been achieved. The aspect is indicated by the case of the object: accusative is telic and partitive is atelic. For example, the (implicit) purpose of shooting is to kill, such that: In rare cases corresponding telic and atelic forms can be unrelated by meaning.
 * Ammuin karhun -- "I shot the bear (succeeded; it is done)" i.e., "I shot the bear dead".
 * Ammuin karhua -- "I shot at the bear" i.e. the bear may have survived.

Derivational suffixes exist for various aspects. Examples:
 * -ahta- ("once"), as in huudahtaa ("to yell once") (used for emotive verbs like "laugh", "smile", "growl", "bark"; is not used for verbs like "shoot", "say", "drink")
 * -ele- "repeatedly" as in ammuskella "to go shooting around"

There are derivational suffixes for verbs, which carry frequentative, momentane, causative, and inchoative aspect meanings. Also, pairs of verbs differing only in transitivity exist.

Reo Rapa
The Rapa language (Reo Rapa) is a mixed language that grew out of Tahitian and Old Rapa among monolingual inhabitants of Rapa Iti. Old Rapa words are still used for grammar and sentence structure, but most common words were replaced by Tahitian words. Rapa is similar to English as they both have specific tense words such as did or do.

 * Past negative: ki’ere /kiʔere/

ki’ere vau i haere i te fare

NEG.PST 1.SG PFV go PREP ART house

'I did not go to a house.'

 * Non-past negative (Regular negative) kāre /kaːre/

kāre tā-koe puta

NEG.NPST ART-2SG book

'You don't have your book.' (Lit. 'Your book doesn't exist')

Hawaiian
The Hawaiian language conveys aspect as follows:

 * The unmarked verb, frequently used, can indicate habitual aspect or perfective aspect in the past.
 * ke + verb + nei is frequently used and conveys the progressive aspect in the present.
 * e + verb + ana conveys the progressive aspect in any tense.
 * ua + verb conveys the perfective aspect but is frequently omitted.

Wuvulu
Wuvulu language is a minority language in Pacific. The Wuvulu verbal aspect is hard to organize because of its number of morpheme combinations and the interaction of semantics between morphemes. Perfective, imperfective negation, simultaneous and habitual are four aspects markers in Wuvulu language.

 * Perfective: The perfective marker -li indicates the action is done before other action.

'But, Barafi had already clearly told them.'

 * Imperfect negation: The marker ta- indicates the action has not done and also doesn't show anything about the action will be done in the future.

'It has not yet come.'

 * Simultaneous: The marker fi indicates the two actions are done at the same time or one action occurs while other action is in progress.

'He held together the two hands of Puleafo while drinking.' (Note: marker ta- is only for singular subject. When the subject is dual or plural, the marker ʔei and i- are used in same situation.)

 * Habitual: The marker fane- can indicate a habitual activity, which means "keep doing something" in English. Example:

'And the thought kept occurring to Faninilo, "who is this particular person?"'

Tokelauan
There are three types of aspects one must consider when analyzing the Tokelauan language: inherent aspect, situation aspect, and viewpoint aspect.

The inherent aspect describes the purpose of a verb and what separates verbs from one another. According to Vendler, inherent aspect can be categorized into four different types: activities, achievements, accomplishments, and states. Simple activities include verbs such as pull, jump, and punch. Some achievements are continue and win. Drive-a-car is an accomplishment while hate is an example of a state. Another way to recognize a state inherent aspect is to note whether or not it changes. For example, if someone were to hate vegetables because they are allergic, this state of hate is unchanging and thus, a state inherent aspect. On the other hand, an achievement, unlike a state, only lasts for a short amount of time. Achievement is the highpoint of an action.

Another type of aspect is situation aspect. Situation aspect is described to be what one is experiencing in his or her life through that circumstance. Therefore, it is his or her understanding of the situation. Situation aspect are abstract terms that are not physically tangible. They are also used based upon one's point of view. For example, a professor may say that a student who comes a minute before each class starts is a punctual student. Based upon the professor's judgment of what punctuality is, he or she may make that assumption of the situation with the student. Situation aspect is firstly divided into states and occurrences, then later subdivided under occurrences into processes and events, and lastly, under events, there are accomplishments and achievements.

The third type of aspect is viewpoint aspect. Viewpoint aspect can be likened to situation aspect such that they both take into consideration one's inferences. However, viewpoint aspect diverges from situation aspect because it is where one decides to view or see such event. A perfect example is the glass metaphor: Is the glass half full or is it half empty. The choice of being half full represents an optimistic viewpoint while the choice of being half empty represents a pessimistic viewpoint. Not only does viewpoint aspect separate into negative and positive, but rather different point of views. Having two people describe a painting can bring about two different viewpoints. One may describe a situation aspect as a perfect or imperfect. A perfect situation aspect entails an event with no reference to time, while an imperfect situation aspect makes a reference to time with the observation.

Torau
Aspect in Torau is marked with post-verbal particles or clitics. While the system for marking the imperfective aspect is complex and highly developed, it is unclear if Torau marks the perfective and neutral viewpoints. The imperfective clitics index one of the core arguments, usually the nominative subject, and follow the rightmost element in a syntactic structure larger than the word. The two distinct forms for marking the imperfective aspect are (i)sa- and e-. While more work needs to be done on this language, the preliminary hypothesis is that (i)sa- encodes the stative imperfective and e- encodes the active imperfective. Reduplication always cooccurs with e-, but it usually does not with (i)sa-. This example below shows these two imperfective aspect markers giving different meanings to similar sentences.

'Peter was dead.'

Pita ma-to maa≈mate=e-la.

Peter RL.3SG-PST {REDUP}≈be.dead=IPFV-3SG

'Peter was dying.'

In Torau, the suffix -to, which must attach to a preverbal particle, may indicate similar meaning to the perfective aspect. In realis clauses, this suffix conveys an event that is entirely in the past and no longer occurring. When -to is used in irrealis clauses, the speaker conveys that the event will definitely occur (Palmer, 2007). Although this suffix is not explicitly stated as a perfective viewpoint marker, the meaning that it contributes is very similar to the perfective viewpoint.

Malay/Indonesian
Like many Austronesian languages, the verbs of the Malay language follow a system of affixes to express changes in meaning. To express the aspects, Malay uses a number of auxiliary verbs:

 * sudah: perfective, 'saya sudah makan' = 'I have [already] eaten'
 * baru: near perfective, 'saya baru makan' = 'I have just eaten'
 * belum: imperfective, 'saya belum makan' = 'I have not eaten'
 * sedang: progressive not implicating an end
 * masih: progressive implicating an end
 * pernah: semelfactive

Philippine languages
Like many Austronesian languages, the verbs of the Philippine languages follow a complex system of affixes to express subtle changes in meaning. However, the verbs in this family of languages are conjugated to express the aspects and not the tenses. Though many of the Philippine languages do not have a fully codified grammar, most of them follow the verb aspects that are demonstrated by Filipino or Tagalog.

Creole languages
Creole languages typically use the unmarked verb for timeless habitual aspect, or for stative aspect, or for perfective aspect in the past. Invariant pre-verbal markers are often used. Non-stative verbs typically can optionally be marked for the progressive, habitual, completive, or irrealis aspect. The progressive in English-based Atlantic Creoles often uses de (from English "be"). Jamaican Creole uses a (from English "are") or de for the present progressive and a combination of the past time marker (did, behn, ehn or wehn) and the progressive marker (a or de) for the past progressive (e.g. did a or wehn de). Haitian Creole uses the progressive marker ap. Some Atlantic Creoles use one marker for both the habitual and progressive aspects. In Tok Pisin, the optional progressive marker follows the verb. Completive markers tend to come from superstrate words like "done" or "finish", and some creoles model the future/irrealis marker on the superstrate word for "go".

American Sign Language
American Sign Language (ASL) is similar to many other sign languages in that it has no grammatical tense but many verbal aspects produced by modifying the base verb sign.

An example is illustrated with the verb TELL. The basic form of this sign is produced with the initial posture of the index finger on the chin, followed by a movement of the hand and finger tip toward the indirect object (the recipient of the telling). Inflected into the unrealized inceptive aspect ("to be just about to tell"), the sign begins with the hand moving from in front of the trunk in an arc to the initial posture of the base sign (i.e., index finger touching the chin) while inhaling through the mouth, dropping the jaw, and directing eye gaze toward the verb's object. The posture is then held rather than moved toward the indirect object. During the hold, the signer also stops the breath by closing the glottis. Other verbs (such as "look at", "wash the dishes", "yell", "flirt") are inflected into the unrealized inceptive aspect similarly: The hands used in the base sign move in an arc from in front of the trunk to the initial posture of the underlying verb sign while inhaling, dropping the jaw, and directing eye gaze toward the verb's object (if any), but subsequent movements and postures are dropped as the posture and breath are held.

Other aspects in ASL include the following: stative, inchoative ("to begin to..."), predispositional ("to tend to..."), susceptative ("to... easily"), frequentative ("to... often"), protractive ("to... continuously"), incessant ("to... incessantly"), durative ("to... for a long time"), iterative ("to... over and over again"), intensive ("to... very much"), resultative ("to... completely"), approximative ("to... somewhat"), semblitive ("to appear to..."), increasing ("to... more and more"). Some aspects combine with others to create yet finer distinctions.

Aspect is unusual in ASL in that transitive verbs derived for aspect lose their grammatical transitivity. They remain semantically transitive, typically assuming an object made prominent using a topic marker or mentioned in a previous sentence. See Syntax in ASL for details.

Terms for various aspects
The following aspectual terms are found in the literature. Approximate English equivalents are given.
 * Perfective: 'I struck the bell' (an event viewed in its entirety, without reference to its temporal structure during its occurrence)
 * Momentane: 'The mouse squeaked once' (contrasted to 'The mouse squeaked / was squeaking')
 * Perfect (a common conflation of aspect and tense): 'I have arrived' (brings attention to the consequences of a situation in the past)
 * Recent perfect, also known as after perfect: 'I just ate' or 'I am after eating' (Hiberno-English)
 * Discontinuous past: In English a sentence such as "I put it on the table" is neutral in implication (the object could still be on the table or not), but in some languages such as Chichewa the equivalent tense carries an implication that the object is no longer there. It is thus the opposite of the perfect aspect.
 * Prospective (a conflation of aspect and tense): 'He is about to fall', 'I am going to cry" (brings attention to the anticipation of a future situation)
 * Imperfective (an activity with ongoing nature: combines the meanings of both the continuous and the habitual aspects): 'I was walking to work' (continuous) or 'I walked (used to walk, would walk) to work every day' (habitual).
 * Habitual: 'I used to walk home from work', 'I would walk home from work every day', 'I walk home from work every day' (a subtype of imperfective)
 * Continuous: 'I am eating' or 'I know' (situation is described as ongoing and either evolving or unevolving; a subtype of imperfective)
 * Progressive: 'I am eating' (action is described as ongoing and evolving; a subtype of continuous)
 * Stative: 'I know French' (situation is described as ongoing but not evolving; a subtype of continuous)
 * Gnomic/generic: 'Fish swim and birds fly' (general truths)
 * Episodic: 'The bird flew' (non-gnomic)
 * Continuative aspect: 'I am still eating'
 * Inceptive/ingressive: 'I started to run' (beginning of a new action: dynamic)
 * Inchoative: 'The flowers started to bloom' (beginning of a new state: static)
 * Terminative/cessative: 'I finished eating/reading'
 * Defective: 'I almost fell'
 * Pausative: 'I stopped working for a while'
 * Resumptive: 'I resumed sleeping'
 * Punctual: 'I slept'
 * Durative/Delimitative: 'I slept for a while'
 * Protractive: 'The argument went on and on'
 * Iterative: 'I read the same books again and again'
 * Frequentative: 'It sparkled', contrasted with 'It sparked'. Or, 'I run around', vs. 'I run'
 * Experiential: 'I have gone to school many times' (see for example Chinese aspects)
 * Intentional: 'I listened carefully'
 * Accidental: 'I accidentally knocked over the chair'
 * Intensive: 'It glared'
 * Attenuative: 'It glimmered'
 * Segmentative: 'It is coming out in successive multitudes'

Other references

 * Routledge Dictionary of Language and Linguistics (ISBN 0-415-20319-8), by Hadumod Bussmann, edited by Gregory P. Trauth and Kerstin Kazzazi, Routledge, London 1996. Translation of German Lexikon der Sprachwissenschaft Kröner Verlag, Stuttgart 1990.
 * Morfofonologian harjoituksia, Lauri Carlson
 * Berdinetto, P. M., & Delfitto, D. (2000). "Aspect vs. Actionality: Some reasons for keeping them apart". In O. Dahl (Ed.), Tense and Aspect in the Languages of Europe (pp. 189–226). Berlin: Mouton de Gruyter.
 * Binnick, R. I. (1991). Time and the verb: A guide to tense and aspect. New York: Oxford University Press.
 * Binnick, R. I. (2006). "Aspect and Aspectuality". In B. Aarts & A. M. S. McMahon (Eds.), The Handbook of English Linguistics (pp. 244–268). Malden, MA: Blackwell Publishing.
 * Comrie, B. (1976). Aspect: An introduction to the study of verbal aspect and related problems. Cambridge; New York: Cambridge University Press.
 * Frawley, W. (1992). Linguistic semantics. Hillsdale, NJ: Lawrence Erlbaum Associates.
 * Kabakciev, K. (2000). Aspect in English: a "common-sense" view of the interplay between verbal and nominal referents (Studies in Linguistics and Philosophy). Springer. Retrieved 2016-05-18.
 * MacDonald, J. E. (2008). The syntactic nature of inner aspect: A minimalist perspective. Amsterdam; Philadelphia: John Benjamins Pub. Co.
 * Maslov, I. S. (1998). "Vid glagol'nyj" ["Aspect of the verb"]. In V. N. Yartseva (Ed.), Jazykoznanie: Bol'shoj entsyklopedicheskij slovar' (pp. 83–84). Moscow: Bol'shaja Rossijskaja Entsyklopedija.
 * Richardson, K. (2007). Case and aspect in Slavic. Oxford; New York: Oxford University Press.
 * Sasse, H.-J. (2006). "Aspect and Aktionsart". In E. K. Brown (Ed.), Encyclopedia of language and linguistics (Vol. 1, pp. 535–538). Boston: Elsevier.
 * Smith, Carlota S. (1991). The parameter of aspect. Dordrecht; Boston: Kluwer Academic Publishers.
 * Travis, Lisa deMena (2010). "Inner aspect", Dordrecht, Springer..
 * Verkuyl, H. (1972). On the Compositional Nature of the Aspects, Reidel, Dordrecht.
 * Verkuyl, H. (1993). A Theory of Aspectuality: the interaction between temporal and atemporal structure. Cambridge: Cambridge University Press.
 * Verkuyl, H. (2005). "How (in-)sensitive is tense to aspectual information?" In B. Hollebrandse, A. van Hout & C. Vet (Eds.), Crosslinguistic views on tense, aspect and modality (pp. 145–169). Amsterdam: Rodopi.
 * Zalizniak, A. A., & Shmelev, A. D. (2000). Vvedenie v russkuiu aspektologiiu [Introduction to Russian aspectology]. Moskva: IAzyki russkoi kul’tury.
 * Travis, Lisa deMena (2010). "Inner aspect", Dordrecht, Springer..
 * Verkuyl, H. (1972). On the Compositional Nature of the Aspects, Reidel, Dordrecht.
 * Verkuyl, H. (1993). A Theory of Aspectuality: the interaction between temporal and atemporal structure. Cambridge: Cambridge University Press.
 * Verkuyl, H. (2005). "How (in-)sensitive is tense to aspectual information?" In B. Hollebrandse, A. van Hout & C. Vet (Eds.), Crosslinguistic views on tense, aspect and modality (pp. 145–169). Amsterdam: Rodopi.
 * Zalizniak, A. A., & Shmelev, A. D. (2000). Vvedenie v russkuiu aspektologiiu [Introduction to Russian aspectology]. Moskva: IAzyki russkoi kul’tury.

title: Grammatical aspect


text: Talk:Gabriel García Márquez

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

title: Talk:Gabriel García Márquez


text:
Glucose

Glucose is a sugar with the molecular formula C6H12O6. Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using energy from sunlight. Glucose is used by plants to make cellulose—the most abundant carbohydrate in the world—for use in cell walls, and by all living organisms to make adenosine triphosphate (ATP), which is used by the cell as energy.

In energy metabolism, glucose is the most important source of energy in all organisms. Glucose for metabolism is stored as a polymer, in plants mainly as starch and amylopectin, and in animals as glycogen. Glucose circulates in the blood of animals as blood sugar. The naturally occurring form of glucose is -glucose, while its stereoisomer -glucose is produced synthetically in comparatively small amounts and is less biologically active. Glucose is a monosaccharide containing six carbon atoms and an aldehyde group, and is therefore an aldohexose. The glucose molecule can exist in an open-chain (acyclic) as well as ring (cyclic) form. Glucose is naturally occurring and is found in its free state in fruits and other parts of plants. In animals, glucose is released from the breakdown of glycogen in a process known as glycogenolysis.

Glucose, as intravenous sugar solution, is on the World Health Organization's List of Essential Medicines. It is also on the list in combination with sodium chloride (table salt).

The name glucose is derived from Ancient Greek γλεῦκος 'wine, must', from γλυκύς  'sweet'. The suffix -ose is a chemical classifier denoting a sugar.

History
Glucose was first isolated from raisins in 1747 by the German chemist Andreas Marggraf. Glucose was discovered in grapes by another German chemist – Johann Tobias Lowitz – in 1792, and distinguished as being different from cane sugar (sucrose). Glucose is the term coined by Jean Baptiste Dumas in 1838, which has prevailed in the chemical literature. Friedrich August Kekulé proposed the term dextrose (from the Latin dexter, meaning "right"), because in aqueous solution of glucose, the plane of linearly polarized light is turned to the right. In contrast, l-fructose (usually referred to as -fructose) (a ketohexose) and l-glucose (-glucose) turn linearly polarized light to the left. The earlier notation according to the rotation of the plane of linearly polarized light (d and l-nomenclature) was later abandoned in favor of the - and -notation, which refers to the absolute configuration of the asymmetric center farthest from the carbonyl group, and in concordance with the configuration of - or -glyceraldehyde.

Since glucose is a basic necessity of many organisms, a correct understanding of its chemical makeup and structure contributed greatly to a general advancement in organic chemistry. This understanding occurred largely as a result of the investigations of Emil Fischer, a German chemist who received the 1902 Nobel Prize in Chemistry for his findings. The synthesis of glucose established the structure of organic material and consequently formed the first definitive validation of Jacobus Henricus van 't Hoff's theories of chemical kinetics and the arrangements of chemical bonds in carbon-bearing molecules. Between 1891 and 1894, Fischer established the stereochemical configuration of all the known sugars and correctly predicted the possible isomers, applying Van 't Hoff's theory of asymmetrical carbon atoms. The names initially referred to the natural substances. Their enantiomers were given the same name with the introduction of systematic nomenclatures, taking into account absolute stereochemistry (e.g. Fischer nomenclature, / nomenclature).

For the discovery of the metabolism of glucose Otto Meyerhof received the Nobel Prize in Physiology or Medicine in 1922. Hans von Euler-Chelpin was awarded the Nobel Prize in Chemistry along with Arthur Harden in 1929 for their "research on the fermentation of sugar and their share of enzymes in this process". In 1947, Bernardo Houssay (for his discovery of the role of the pituitary gland in the metabolism of glucose and the derived carbohydrates) as well as Carl and Gerty Cori (for their discovery of the conversion of glycogen from glucose) received the Nobel Prize in Physiology or Medicine. In 1970, Luis Leloir was awarded the Nobel Prize in Chemistry for the discovery of glucose-derived sugar nucleotides in the biosynthesis of carbohydrates.

Chemical and physical properties
Glucose forms white or colorless solids that are highly soluble in water and acetic acid but poorly soluble in methanol and ethanol. They melt at 146 C (α) and 150 C (beta), decompose starting at 188 C with release of various volatile products, ultimately leaving a residue of carbon. Glucose has a pKa value of 12.16 at 25 C in water.

With six carbon atoms, it is classed as a hexose, a subcategory of the monosaccharides. -Glucose is one of the sixteen aldohexose stereoisomers. The -isomer, -glucose, also known as dextrose, occurs widely in nature, but the -isomer, -glucose, does not. Glucose can be obtained by hydrolysis of carbohydrates such as milk sugar (lactose), cane sugar (sucrose), maltose, cellulose, glycogen, etc. Dextrose is commonly commercially manufactured from starches, such as corn starch in the US and Japan, from potato and wheat starch in Europe, and from tapioca starch in tropical areas. The manufacturing process uses hydrolysis via pressurized steaming at controlled pH in a jet followed by further enzymatic depolymerization. Unbonded glucose is one of the main ingredients of honey.

The term dextrose is often used in a clinical (related to patient's health status) or nutritional context (related to dietary intake, such as food labels or dietary guidelines), while "glucose" is used in a biological or physiological context (chemical processes and molecular interactions), but both terms refer to the same molecule, specifically D-glucose.

Dextrose monohydrate is the hydrated form of D-glucose, meaning that it is a glucose molecule with an additional water molecule attached. Its chemical formula is C6H12O6 · H2O. Dextrose monohydrate is also called hydrated D-glucose, and commonly manufactured from plant starches. Dextrose monohydrate is utilized as the predominant type of dextrose in food applications, such as beverage mixes—it is a common form of glucose widely used as a nutrition supplement in production of foodstuffs. Dextrose monohydrate is primarily consumed in North America as a corn syrup or high-fructose corn syrup.

Anhydrous dextrose, on the other hand, is glucose that does not have any water molecules attached to it. Anhydrous chemical substances are commonly produced by eliminating water from a hydrated substance through methods such as heating or drying up (desiccation). Dextrose monohydrate can be dehydrated to anhydrous dextrose in industrial setting. Dextrose monohydrate is composed of approximately 9.5% water by mass; through the process of dehydration, this water content is eliminated to yield anhydrous (dry) dextrose.

Anhydrous dextrose has the chemical formula C6H12O6, without any water molecule attached which is the same as glucose. Anhydrous dextrose on open air tends to absorb moisture and transform to the monohydrate, and it is more expensive to produce. Anhydrous dextrose (anhydrous D-glucose) has increased stability and increased shelf life, has medical applications, such as in oral glucose tolerance test (OGTT).

Whereas molecular weight (molar mass) for D-glucose monohydrate is 198.17 g/mol, that for anhydrous D-glucose is 180.16 g/mol   The density of these two forms of glucose is also different.

In terms of chemical structure, glucose is a monosaccharide, that is, a simple sugar. Glucose contains six carbon atoms and an aldehyde group, and is therefore an aldohexose. The glucose molecule can exist in an open-chain (acyclic) as well as ring (cyclic) form—due to the presence of alcohol and aldehyde or ketone functional groups, the form having the straight chain can easily convert into a chair-like hemiacetal ring structure commonly found in carbohydrates.

Structure and nomenclature

Glucose is present in solid form as a monohydrate with a closed pyran ring (α-glucopyranose monohydrate, sometimes known less precisely by dextrose hydrate). In aqueous solution, on the other hand, it is an open-chain to a small extent and is present predominantly as α- or β-pyranose, which interconvert. From aqueous solutions, the three known forms can be crystallized: α-glucopyranose, β-glucopyranose and α-glucopyranose monohydrate. Glucose is a building block of the disaccharides lactose and sucrose (cane or beet sugar), of oligosaccharides such as raffinose and of polysaccharides such as starch, amylopectin, glycogen, and cellulose. The glass transition temperature of glucose is 31 C and the Gordon–Taylor constant (an experimentally determined constant for the prediction of the glass transition temperature for different mass fractions of a mixture of two substances) is 4.5.

Open-chain form
A open-chain form of glucose makes up less than 0.02% of the glucose molecules in an aqueous solution at equilibrium. The rest is one of two cyclic hemiacetal forms. In its open-chain form, the glucose molecule has an open (as opposed to cyclic) unbranched backbone of six carbon atoms, where C-1 is part of an aldehyde group H(C\dO)\s. Therefore, glucose is also classified as an aldose, or an aldohexose. The aldehyde group makes glucose a reducing sugar giving a positive reaction with the Fehling test.

Cyclic forms
In solutions, the open-chain form of glucose (either "D-" or "L-") exists in equilibrium with several cyclic isomers, each containing a ring of carbons closed by one oxygen atom. In aqueous solution, however, more than 99% of glucose molecules exist as pyranose forms. The open-chain form is limited to about 0.25%, and furanose forms exist in negligible amounts. The terms "glucose" and "D-glucose" are generally used for these cyclic forms as well. The ring arises from the open-chain form by an intramolecular nucleophilic addition reaction between the aldehyde group (at C-1) and either the C-4 or C-5 hydroxyl group, forming a hemiacetal linkage, \sC(OH)H\sO\s.

The reaction between C-1 and C-5 yields a six-membered heterocyclic system called a pyranose, which is a monosaccharide sugar (hence "-ose") containing a derivatised pyran skeleton. The (much rarer) reaction between C-1 and C-4 yields a five-membered furanose ring, named after the cyclic ether furan. In either case, each carbon in the ring has one hydrogen and one hydroxyl attached, except for the last carbon (C-4 or C-5) where the hydroxyl is replaced by the remainder of the open molecule (which is \s(C(CH2OH)HOH)\sH or \s(CHOH)\sH respectively).

The ring-closing reaction can give two products, denoted "α-" and "β-". When a glucopyranose molecule is drawn in the Haworth projection, the designation "α-" means that the hydroxyl group attached to C-1 and the \sCH2OH group at C-5 lies on opposite sides of the ring's plane (a trans arrangement), while "β-" means that they are on the same side of the plane (a cis arrangement). Therefore, the open-chain isomer D-glucose gives rise to four distinct cyclic isomers: α-D-glucopyranose, β-D-glucopyranose, α-D-glucofuranose, and β-D-glucofuranose. These five structures exist in equilibrium and interconvert, and the interconversion is much more rapid with acid catalysis.

The other open-chain isomer L-glucose similarly gives rise to four distinct cyclic forms of L-glucose, each the mirror image of the corresponding D-glucose.

The glucopyranose ring (α or β) can assume several non-planar shapes, analogous to the "chair" and "boat" conformations of cyclohexane. Similarly, the glucofuranose ring may assume several shapes, analogous to the "envelope" conformations of cyclopentane.

In the solid state, only the glucopyranose forms are observed.

Some derivatives of glucofuranose, such as 1,2-O-isopropylidene--glucofuranose are stable and can be obtained pure as crystalline solids. For example, reaction of α-D-glucose with para-tolylboronic acid H3C\s(C6H4)\sB(OH)2 reforms the normal pyranose ring to yield the 4-fold ester α-D-glucofuranose-1,2:3,5-bis(p-tolylboronate).

Mutarotation
Mutarotation consists of a temporary reversal of the ring-forming reaction, resulting in the open-chain form, followed by a reforming of the ring. The ring closure step may use a different \sOH group than the one recreated by the opening step (thus switching between pyranose and furanose forms), or the new hemiacetal group created on C-1 may have the same or opposite handedness as the original one (thus switching between the α and β forms). Thus, though the open-chain form is barely detectable in solution, it is an essential component of the equilibrium.

The open-chain form is thermodynamically unstable, and it spontaneously isomerizes to the cyclic forms. (Although the ring closure reaction could in theory create four- or three-atom rings, these would be highly strained, and are not observed in practice.) In solutions at room temperature, the four cyclic isomers interconvert over a time scale of hours, in a process called mutarotation. Starting from any proportions, the mixture converges to a stable ratio of α:β 36:64. The ratio would be α:β 11:89 if it were not for the influence of the anomeric effect. Mutarotation is considerably slower at temperatures close to 0 C.

Optical activity
Whether in water or the solid form, -(+)-glucose is dextrorotatory, meaning it will rotate the direction of polarized light clockwise as seen looking toward the light source. The effect is due to the chirality of the molecules, and indeed the mirror-image isomer, -(−)-glucose, is levorotatory (rotates polarized light counterclockwise) by the same amount. The strength of the effect is different for each of the five tautomers.

Note that the - prefix does not refer directly to the optical properties of the compound. It indicates that the C-5 chiral centre has the same handedness as that of -glyceraldehyde (which was so labelled because it is dextrorotatory). The fact that -glucose is dextrorotatory is a combined effect of its four chiral centres, not just of C-5; and indeed some of the other -aldohexoses are levorotatory.

The conversion between the two anomers can be observed in a polarimeter since pure α--glucose has a specific rotation angle of +112.2° mL/(dm·g), pure β--glucose of +17.5° mL/(dm·g). When equilibrium has been reached after a certain time due to mutarotation, the angle of rotation is +52.7° mL/(dm·g). By adding acid or base, this transformation is much accelerated. The equilibration takes place via the open-chain aldehyde form.

Isomerisation
In dilute sodium hydroxide or other dilute bases, the monosaccharides mannose, glucose and fructose interconvert (via a Lobry de Bruyn–Alberda–Van Ekenstein transformation), so that a balance between these isomers is formed. This reaction proceeds via an enediol:

Biochemical properties
Glucose is the most abundant monosaccharide. Glucose is also the most widely used aldohexose in most living organisms. One possible explanation for this is that glucose has a lower tendency than other aldohexoses to react nonspecifically with the amine groups of proteins. This reaction—glycation—impairs or destroys the function of many proteins, e.g. in glycated hemoglobin. Glucose's low rate of glycation can be attributed to its having a more stable cyclic form compared to other aldohexoses, which means it spends less time than they do in its reactive open-chain form. The reason for glucose having the most stable cyclic form of all the aldohexoses is that its hydroxy groups (with the exception of the hydroxy group on the anomeric carbon of -glucose) are in the equatorial position. Presumably, glucose is the most abundant natural monosaccharide because it is less glycated with proteins than other monosaccharides. Another hypothesis is that glucose, being the only -aldohexose that has all five hydroxy substituents in the equatorial position in the form of β--glucose, is more readily accessible to chemical reactions, for example, for esterification  or acetal formation. For this reason, -glucose is also a highly preferred building block in natural polysaccharides (glycans). Polysaccharides that are composed solely of glucose are termed glucans.

Glucose is produced by plants through photosynthesis using sunlight, water and carbon dioxide and can be used by all living organisms as an energy and carbon source. However, most glucose does not occur in its free form, but in the form of its polymers, i.e. lactose, sucrose, starch and others which are energy reserve substances, and cellulose and chitin, which are components of the cell wall in plants or fungi and arthropods, respectively. These polymers, when consumed by animals, fungi and bacteria, are degraded to glucose using enzymes. All animals are also able to produce glucose themselves from certain precursors as the need arises. Neurons, cells of the renal medulla and erythrocytes depend on glucose for their energy production. In adult humans, there is about 18 g of glucose, of which about 4 g is present in the blood. Approximately 180-220 g of glucose is produced in the liver of an adult in 24 hours.

Many of the long-term complications of diabetes (e.g., blindness, kidney failure, and peripheral neuropathy) are probably due to the glycation of proteins or lipids. In contrast, enzyme-regulated addition of sugars to protein is called glycosylation and is essential for the function of many proteins.

Uptake
Ingested glucose initially binds to the receptor for sweet taste on the tongue in humans. This complex of the proteins T1R2 and T1R3 makes it possible to identify glucose-containing food sources. Glucose mainly comes from food—about 300 g per day is produced by conversion of food, but it is also synthesized from other metabolites in the body's cells. In humans, the breakdown of glucose-containing polysaccharides happens in part already during chewing by means of amylase, which is contained in saliva, as well as by maltase, lactase, and sucrase on the brush border of the small intestine. Glucose is a building block of many carbohydrates and can be split off from them using certain enzymes. Glucosidases, a subgroup of the glycosidases, first catalyze the hydrolysis of long-chain glucose-containing polysaccharides, removing terminal glucose. In turn, disaccharides are mostly degraded by specific glycosidases to glucose. The names of the degrading enzymes are often derived from the particular poly- and disaccharide; inter alia, for the degradation of polysaccharide chains there are amylases (named after amylose, a component of starch), cellulases (named after cellulose), chitinases (named after chitin), and more. Furthermore, for the cleavage of disaccharides, there are maltase, lactase, sucrase, trehalase, and others. In humans, about 70 genes are known that code for glycosidases. They have functions in the digestion and degradation of glycogen, sphingolipids, mucopolysaccharides, and poly(ADP-ribose). Humans do not produce cellulases, chitinases, or trehalases, but the bacteria in the gut microbiota do.

In order to get into or out of cell membranes of cells and membranes of cell compartments, glucose requires special transport proteins from the major facilitator superfamily. In the small intestine (more precisely, in the jejunum), glucose is taken up into the intestinal epithelium with the help of glucose transporters via a secondary active transport mechanism called sodium ion-glucose symport via sodium/glucose cotransporter 1 (SGLT1). Further transfer occurs on the basolateral side of the intestinal epithelial cells via the glucose transporter GLUT2, as well uptake into liver cells, kidney cells, cells of the islets of Langerhans, neurons, astrocytes, and tanycytes. Glucose enters the liver via the portal vein and is stored there as a cellular glycogen. In the liver cell, it is phosphorylated by glucokinase at position 6 to form glucose 6-phosphate, which cannot leave the cell. Glucose 6-phosphatase can convert glucose 6-phosphate back into glucose exclusively in the liver, so the body can maintain a sufficient blood glucose concentration. In other cells, uptake happens by passive transport through one of the 14 GLUT proteins. In the other cell types, phosphorylation occurs through a hexokinase, whereupon glucose can no longer diffuse out of the cell.

The glucose transporter GLUT1 is produced by most cell types and is of particular importance for nerve cells and pancreatic β-cells. GLUT3 is highly expressed in nerve cells. Glucose from the bloodstream is taken up by GLUT4 from muscle cells (of the skeletal muscle and heart muscle) and fat cells. GLUT14 is expressed exclusively in testicles. Excess glucose is broken down and converted into fatty acids, which are stored as triglycerides. In the kidneys, glucose in the urine is absorbed via SGLT1 and SGLT2 in the apical cell membranes and transmitted via GLUT2 in the basolateral cell membranes. About 90% of kidney glucose reabsorption is via SGLT2 and about 3% via SGLT1.

Biosynthesis
In plants and some prokaryotes, glucose is a product of photosynthesis. Glucose is also formed by the breakdown of polymeric forms of glucose like glycogen (in animals and mushrooms) or starch (in plants). The cleavage of glycogen is termed glycogenolysis, the cleavage of starch is called starch degradation.

The metabolic pathway that begins with molecules containing two to four carbon atoms (C) and ends in the glucose molecule containing six carbon atoms is called gluconeogenesis and occurs in all living organisms. The smaller starting materials are the result of other metabolic pathways. Ultimately almost all biomolecules come from the assimilation of carbon dioxide in plants and microbes during photosynthesis. The free energy of formation of α--glucose is 917.2 kilojoules per mole. In humans, gluconeogenesis occurs in the liver and kidney, but also in other cell types. In the liver about 150 g of glycogen are stored, in skeletal muscle about 250 g. However, the glucose released in muscle cells upon cleavage of the glycogen can not be delivered to the circulation because glucose is phosphorylated by the hexokinase, and a glucose-6-phosphatase is not expressed to remove the phosphate group. Unlike for glucose, there is no transport protein for glucose-6-phosphate. Gluconeogenesis allows the organism to build up glucose from other metabolites, including lactate or certain amino acids, while consuming energy. The renal tubular cells can also produce glucose.

Glucose also can be found outside of living organisms in the ambient environment. Glucose concentrations in the atmosphere are detected via collection of samples by aircraft and are known to vary from location to location. For example, glucose concentrations in atmospheric air from inland China range from 0.8 to 20.1 pg/L, whereas east coastal China glucose concentrations range from 10.3 to 142 pg/L.

Glucose degradation

In humans, glucose is metabolized by glycolysis and the pentose phosphate pathway. Glycolysis is used by all living organisms, with small variations, and all organisms generate energy from the breakdown of monosaccharides. In the further course of the metabolism, it can be completely degraded via oxidative decarboxylation, the citric acid cycle (synonym Krebs cycle) and the respiratory chain to water and carbon dioxide. If there is not enough oxygen available for this, the glucose degradation in animals occurs anaerobic to lactate via lactic acid fermentation and releases much less energy. Muscular lactate enters the liver through the bloodstream in mammals, where gluconeogenesis occurs (Cori cycle). With a high supply of glucose, the metabolite acetyl-CoA from the Krebs cycle can also be used for fatty acid synthesis. Glucose is also used to replenish the body's glycogen stores, which are mainly found in liver and skeletal muscle. These processes are hormonally regulated.

In other living organisms, other forms of fermentation can occur. The bacterium Escherichia coli can grow on nutrient media containing glucose as the sole carbon source. In some bacteria and, in modified form, also in archaea, glucose is degraded via the Entner-Doudoroff pathway. With Glucose, a mechanism for gene regulation was discovered in E. coli, the catabolite repression (formerly known as glucose effect).

Use of glucose as an energy source in cells is by either aerobic respiration, anaerobic respiration, or fermentation. The first step of glycolysis is the phosphorylation of glucose by a hexokinase to form glucose 6-phosphate. The main reason for the immediate phosphorylation of glucose is to prevent its diffusion out of the cell as the charged phosphate group prevents glucose 6-phosphate from easily crossing the cell membrane. Furthermore, addition of the high-energy phosphate group activates glucose for subsequent breakdown in later steps of glycolysis.

In anaerobic respiration, one glucose molecule produces a net gain of two ATP molecules (four ATP molecules are produced during glycolysis through substrate-level phosphorylation, but two are required by enzymes used during the process). In aerobic respiration, a molecule of glucose is much more profitable in that a maximum net production of 30 or 32 ATP molecules (depending on the organism) is generated.

Tumor cells often grow comparatively quickly and consume an above-average amount of glucose by glycolysis, which leads to the formation of lactate, the end product of fermentation in mammals, even in the presence of oxygen. This is called the Warburg effect. For the increased uptake of glucose in tumors various SGLT and GLUT are overly produced.

In yeast, ethanol is fermented at high glucose concentrations, even in the presence of oxygen (which normally leads to respiration rather than fermentation). This is called the Crabtree effect.

Glucose can also degrade to form carbon dioxide through abiotic means. This has been demonstrated to occur experimentally via oxidation and hydrolysis at 22 °C and a pH of 2.5.

Energy source
Glucose is a ubiquitous fuel in biology. It is used as an energy source in organisms, from bacteria to humans, through either aerobic respiration, anaerobic respiration (in bacteria), or fermentation. Glucose is the human body's key source of energy, through aerobic respiration, providing about 3.75 kilocalories (16 kilojoules) of food energy per gram. Breakdown of carbohydrates (e.g., starch) yields mono- and disaccharides, most of which is glucose. Through glycolysis and later in the reactions of the citric acid cycle and oxidative phosphorylation, glucose is oxidized to eventually form carbon dioxide and water, yielding energy mostly in the form of adenosine triphosphate (ATP). The insulin reaction, and other mechanisms, regulate the concentration of glucose in the blood. The physiological caloric value of glucose, depending on the source, is 16.2 kilojoules per gram or 15.7 kJ/g (3.74 kcal/g). The high availability of carbohydrates from plant biomass has led to a variety of methods during evolution, especially in microorganisms, to utilize glucose for energy and carbon storage. Differences exist in which end product can no longer be used for energy production. The presence of individual genes, and their gene products, the enzymes, determine which reactions are possible. The metabolic pathway of glycolysis is used by almost all living beings. An essential difference in the use of glycolysis is the recovery of NADPH as a reductant for anabolism that would otherwise have to be generated indirectly.

Glucose and oxygen supply almost all the energy for the brain, so its availability influences psychological processes. When glucose is low, psychological processes requiring mental effort (e.g., self-control, effortful decision-making) are impaired. In the brain, which is dependent on glucose and oxygen as the major source of energy, the glucose concentration is usually 4 to 6 mM (5 mM equals 90 mg/dL), but decreases to 2 to 3 mM when fasting. Confusion occurs below 1 mM and coma at lower levels.

The glucose in the blood is called blood sugar. Blood sugar levels are regulated by glucose-binding nerve cells in the hypothalamus. In addition, glucose in the brain binds to glucose receptors of the reward system in the nucleus accumbens. The binding of glucose to the sweet receptor on the tongue induces a release of various hormones of energy metabolism, either through glucose or through other sugars, leading to an increased cellular uptake and lower blood sugar levels. Artificial sweeteners do not lower blood sugar levels.

The blood sugar content of a healthy person in the short-time fasting state, e.g. after overnight fasting, is about 70 to 100 mg/dL of blood (4 to 5.5 mM). In blood plasma, the measured values are about 10–15% higher. In addition, the values in the arterial blood are higher than the concentrations in the venous blood since glucose is absorbed into the tissue during the passage of the capillary bed. Also in the capillary blood, which is often used for blood sugar determination, the values are sometimes higher than in the venous blood. The glucose content of the blood is regulated by the hormones insulin, incretin and glucagon. Insulin lowers the glucose level, glucagon increases it. Furthermore, the hormones adrenaline, thyroxine, glucocorticoids, somatotropin and adrenocorticotropin lead to an increase in the glucose level. There is also a hormone-independent regulation, which is referred to as glucose autoregulation. After food intake the blood sugar concentration increases. Values over 180 mg/dL in venous whole blood are pathological and are termed hyperglycemia, values below 40 mg/dL are termed hypoglycaemia. When needed, glucose is released into the bloodstream by glucose-6-phosphatase from glucose-6-phosphate originating from liver and kidney glycogen, thereby regulating the homeostasis of blood glucose concentration. In ruminants, the blood glucose concentration is lower (60 mg/dL in cattle and 40 mg/dL in sheep), because the carbohydrates are converted more by their gut microbiota into short-chain fatty acids.

Some glucose is converted to lactic acid by astrocytes, which is then utilized as an energy source by brain cells; some glucose is used by intestinal cells and red blood cells, while the rest reaches the liver, adipose tissue and muscle cells, where it is absorbed and stored as glycogen (under the influence of insulin). Liver cell glycogen can be converted to glucose and returned to the blood when insulin is low or absent; muscle cell glycogen is not returned to the blood because of a lack of enzymes. In fat cells, glucose is used to power reactions that synthesize some fat types and have other purposes. Glycogen is the body's "glucose energy storage" mechanism, because it is much more "space efficient" and less reactive than glucose itself.

As a result of its importance in human health, glucose is an analyte in glucose tests that are common medical blood tests. Eating or fasting prior to taking a blood sample has an effect on analyses for glucose in the blood; a high fasting glucose blood sugar level may be a sign of prediabetes or diabetes mellitus.

The glycemic index is an indicator of the speed of resorption and conversion to blood glucose levels from ingested carbohydrates, measured as the area under the curve of blood glucose levels after consumption in comparison to glucose (glucose is defined as 100). The clinical importance of the glycemic index is controversial, as foods with high fat contents slow the resorption of carbohydrates and lower the glycemic index, e.g. ice cream. An alternative indicator is the insulin index, measured as the impact of carbohydrate consumption on the blood insulin levels. The glycemic load is an indicator for the amount of glucose added to blood glucose levels after consumption, based on the glycemic index and the amount of consumed food.

Precursor
Organisms use glucose as a precursor for the synthesis of several important substances. Starch, cellulose, and glycogen ("animal starch") are common glucose polymers (polysaccharides). Some of these polymers (starch or glycogen) serve as energy stores, while others (cellulose and chitin, which is made from a derivative of glucose) have structural roles. Oligosaccharides of glucose combined with other sugars serve as important energy stores. These include lactose, the predominant sugar in milk, which is a glucose-galactose disaccharide, and sucrose, another disaccharide which is composed of glucose and fructose. Glucose is also added onto certain proteins and lipids in a process called glycosylation. This is often critical for their functioning. The enzymes that join glucose to other molecules usually use phosphorylated glucose to power the formation of the new bond by coupling it with the breaking of the glucose-phosphate bond.

Other than its direct use as a monomer, glucose can be broken down to synthesize a wide variety of other biomolecules. This is important, as glucose serves both as a primary store of energy and as a source of organic carbon. Glucose can be broken down and converted into lipids. It is also a precursor for the synthesis of other important molecules such as vitamin C (ascorbic acid). In living organisms, glucose is converted to several other chemical compounds that are the starting material for various metabolic pathways. Among them, all other monosaccharides such as fructose (via the polyol pathway), mannose (the epimer of glucose at position 2), galactose (the epimer at position 4), fucose, various uronic acids and the amino sugars are produced from glucose. In addition to the phosphorylation to glucose-6-phosphate, which is part of the glycolysis, glucose can be oxidized during its degradation to glucono-1,5-lactone. Glucose is used in some bacteria as a building block in the trehalose or the dextran biosynthesis and in animals as a building block of glycogen. Glucose can also be converted from bacterial xylose isomerase to fructose. In addition, glucose metabolites produce all nonessential amino acids, sugar alcohols such as mannitol and sorbitol, fatty acids, cholesterol and nucleic acids. Finally, glucose is used as a building block in the glycosylation of proteins to glycoproteins, glycolipids, peptidoglycans, glycosides and other substances (catalyzed by glycosyltransferases) and can be cleaved from them by glycosidases.

Diabetes
Diabetes is a metabolic disorder where the body is unable to regulate levels of glucose in the blood either because of a lack of insulin in the body or the failure, by cells in the body, to respond properly to insulin. Each of these situations can be caused by persistently high elevations of blood glucose levels, through pancreatic burnout and insulin resistance. The pancreas is the organ responsible for the secretion of the hormones insulin and glucagon. Insulin is a hormone that regulates glucose levels, allowing the body's cells to absorb and use glucose. Without it, glucose cannot enter the cell and therefore cannot be used as fuel for the body's functions. If the pancreas is exposed to persistently high elevations of blood glucose levels, the insulin-producing cells in the pancreas could be damaged, causing a lack of insulin in the body. Insulin resistance occurs when the pancreas tries to produce more and more insulin in response to persistently elevated blood glucose levels. Eventually, the rest of the body becomes resistant to the insulin that the pancreas is producing, thereby requiring more insulin to achieve the same blood glucose-lowering effect, and forcing the pancreas to produce even more insulin to compete with the resistance. This negative spiral contributes to pancreatic burnout, and the disease progression of diabetes.

To monitor the body's response to blood glucose-lowering therapy, glucose levels can be measured. Blood glucose monitoring can be performed by multiple methods, such as the fasting glucose test which measures the level of glucose in the blood after 8 hours of fasting. Another test is the 2-hour glucose tolerance test (GTT) – for this test, the person has a fasting glucose test done, then drinks a 75-gram glucose drink and is retested. This test measures the ability of the person's body to process glucose. Over time the blood glucose levels should decrease as insulin allows it to be taken up by cells and exit the blood stream.

Hypoglycemia management
Individuals with diabetes or other conditions that result in low blood sugar often carry small amounts of sugar in various forms. One sugar commonly used is glucose, often in the form of glucose tablets (glucose pressed into a tablet shape sometimes with one or more other ingredients as a binder), hard candy, or sugar packet.

Commercial production
Glucose is produced industrially from starch by enzymatic hydrolysis using glucose amylase or by the use of acids. Enzymatic hydrolysis has largely displaced acid-catalyzed hydrolysis reactions. The result is glucose syrup (enzymatically with more than 90% glucose in the dry matter) with an annual worldwide production volume of 20 million tonnes (as of 2011). This is the reason for the former common name "starch sugar". The amylases most often come from Bacillus licheniformis or Bacillus subtilis (strain MN-385), which are more thermostable than the originally used enzymes. Starting in 1982, pullulanases from Aspergillus niger were used in the production of glucose syrup to convert amylopectin to starch (amylose), thereby increasing the yield of glucose. The reaction is carried out at a pH = 4.6–5.2 and a temperature of 55–60 °C. Corn syrup has between 20% and 95% glucose in the dry matter. The Japanese form of the glucose syrup, Mizuame, is made from sweet potato or rice starch. Maltodextrin contains about 20% glucose.

Many crops can be used as the source of starch. Maize, rice, wheat, cassava, potato, barley, sweet potato, corn husk and sago are all used in various parts of the world. In the United States, corn starch (from maize) is used almost exclusively. Some commercial glucose occurs as a component of invert sugar, a roughly 1:1 mixture of glucose and fructose that is produced from sucrose. In principle, cellulose could be hydrolyzed to glucose, but this process is not yet commercially practical.

Conversion to fructose
In the US, almost exclusively corn (more precisely, corn syrup) is used as glucose source for the production of isoglucose, which is a mixture of glucose and fructose, since fructose has a higher sweetening power – with same physiological calorific value of 374 kilocalories per 100 g. The annual world production of isoglucose is 8 million tonnes (as of 2011). When made from corn syrup, the final product is high-fructose corn syrup (HFCS).

Commercial usage
Glucose is mainly used for the production of fructose and of glucose-containing foods. In foods, it is used as a sweetener, humectant, to increase the volume and to create a softer mouthfeel. Various sources of glucose, such as grape juice (for wine) or malt (for beer), are used for fermentation to ethanol during the production of alcoholic beverages. Most soft drinks in the US use HFCS-55 (with a fructose content of 55% in the dry mass), while most other HFCS-sweetened foods in the US use HFCS-42 (with a fructose content of 42% in the dry mass). In Mexico, on the other hand, soft drinks are sweetened by cane sugar, which has a higher sweetening power. In addition, glucose syrup is used, inter alia, in the production of confectionery such as candies, toffee and fondant. Typical chemical reactions of glucose when heated under water-free conditions are caramelization and, in presence of amino acids, the Maillard reaction.

In addition, various organic acids can be biotechnologically produced from glucose, for example by fermentation with Clostridium thermoaceticum to produce acetic acid, with Penicillium notatum for the production of araboascorbic acid, with Rhizopus delemar for the production of fumaric acid, with Aspergillus niger for the production of gluconic acid, with Candida brumptii to produce isocitric acid, with Aspergillus terreus for the production of itaconic acid, with Pseudomonas fluorescens for the production of 2-ketogluconic acid, with Gluconobacter suboxydans for the production of 5-ketogluconic acid, with Aspergillus oryzae for the production of kojic acid, with Lactobacillus delbrueckii for the production of lactic acid, with Lactobacillus brevis for the production of malic acid, with Propionibacter shermanii for the production of propionic acid, with Pseudomonas aeruginosa for the production of pyruvic acid and with Gluconobacter suboxydans for the production of tartaric acid. Potent, bioactive natural products like triptolide that inhibit mammalian transcription via inhibition of the XPB subunit of the general transcription factor TFIIH has been recently reported as a glucose conjugate for targeting hypoxic cancer cells with increased glucose transporter expression. Recently, glucose has been gaining commercial use as a key component of "kits" containing lactic acid and insulin intended to induce hypoglycemia and hyperlactatemia to combat different cancers and infections.

Analysis
When a glucose molecule is to be detected at a certain position in a larger molecule, nuclear magnetic resonance spectroscopy, X-ray crystallography analysis or lectin immunostaining is performed with concanavalin A reporter enzyme conjugate, which binds only glucose or mannose.

Classical qualitative detection reactions
These reactions have only historical significance:

Fehling test
The Fehling test is a classic method for the detection of aldoses. Due to mutarotation, glucose is always present to a small extent as an open-chain aldehyde. By adding the Fehling reagents (Fehling (I) solution and Fehling (II) solution), the aldehyde group is oxidized to a carboxylic acid, while the Cu2+ tartrate complex is reduced to Cu+ and forms a brick red precipitate (Cu2O).

Tollens test
In the Tollens test, after addition of ammoniacal AgNO3 to the sample solution, glucose reduces Ag+ to elemental silver.

Barfoed test
In Barfoed's test, a solution of dissolved copper acetate, sodium acetate and acetic acid is added to the solution of the sugar to be tested and subsequently heated in a water bath for a few minutes. Glucose and other monosaccharides rapidly produce a reddish color and reddish brown copper(I) oxide (Cu2O).

Nylander's test
As a reducing sugar, glucose reacts in the Nylander's test.

Other tests
Upon heating a dilute potassium hydroxide solution with glucose to 100 °C, a strong reddish browning and a caramel-like odor develops. Concentrated sulfuric acid dissolves dry glucose without blackening at room temperature forming sugar sulfuric acid. In a yeast solution, alcoholic fermentation produces carbon dioxide in the ratio of 2.0454 molecules of glucose to one molecule of CO2. Glucose forms a black mass with stannous chloride. In an ammoniacal silver solution, glucose (as well as lactose and dextrin) leads to the deposition of silver. In an ammoniacal lead acetate solution, white lead glycoside is formed in the presence of glucose, which becomes less soluble on cooking and turns brown. In an ammoniacal copper solution, yellow copper oxide hydrate is formed with glucose at room temperature, while red copper oxide is formed during boiling (same with dextrin, except for with an ammoniacal copper acetate solution). With Hager's reagent, glucose forms mercury oxide during boiling. An alkaline bismuth solution is used to precipitate elemental, black-brown bismuth with glucose. Glucose boiled in an ammonium molybdate solution turns the solution blue. A solution with indigo carmine and sodium carbonate destains when boiled with glucose.

Refractometry and polarimetry
In concentrated solutions of glucose with a low proportion of other carbohydrates, its concentration can be determined with a polarimeter. For sugar mixtures, the concentration can be determined with a refractometer, for example in the Oechsle determination in the course of the production of wine.

Photometric enzymatic methods in solution
The enzyme glucose oxidase (GOx) converts glucose into gluconic acid and hydrogen peroxide while consuming oxygen. Another enzyme, peroxidase, catalyzes a chromogenic reaction (Trinder reaction) of phenol with 4-aminoantipyrine to a purple dye.

Photometric test-strip method
The test-strip method employs the above-mentioned enzymatic conversion of glucose to gluconic acid to form hydrogen peroxide. The reagents are immobilised on a polymer matrix, the so-called test strip, which assumes a more or less intense color. This can be measured reflectometrically at 510 nm with the aid of an LED-based handheld photometer. This allows routine blood sugar determination by nonscientists. In addition to the reaction of phenol with 4-aminoantipyrine, new chromogenic reactions have been developed that allow photometry at higher wavelengths (550 nm, 750 nm).

Amperometric glucose sensor
The electroanalysis of glucose is also based on the enzymatic reaction mentioned above. The produced hydrogen peroxide can be amperometrically quantified by anodic oxidation at a potential of 600 mV. The GOx is immobilized on the electrode surface or in a membrane placed close to the electrode. Precious metals such as platinum or gold are used in electrodes, as well as carbon nanotube electrodes, which e.g. are doped with boron. Cu–CuO nanowires are also used as enzyme-free amperometric electrodes, reaching a detection limit of 50 μmol/L. A particularly promising method is the so-called "enzyme wiring", where the electron flowing during the oxidation is transferred via a molecular wire directly from the enzyme to the electrode.

Other sensory methods
There are a variety of other chemical sensors for measuring glucose. Given the importance of glucose analysis in the life sciences, numerous optical probes have also been developed for saccharides based on the use of boronic acids, which are particularly useful for intracellular sensory applications where other (optical) methods are not or only conditionally usable. In addition to the organic boronic acid derivatives, which often bind highly specifically to the 1,2-diol groups of sugars, there are also other probe concepts classified by functional mechanisms which use selective glucose-binding proteins (e.g. concanavalin A) as a receptor. Furthermore, methods were developed which indirectly detect the glucose concentration via the concentration of metabolized products, e.g. by the consumption of oxygen using fluorescence-optical sensors. Finally, there are enzyme-based concepts that use the intrinsic absorbance or fluorescence of (fluorescence-labeled) enzymes as reporters.

Copper iodometry
Glucose can be quantified by copper iodometry.

Chromatographic methods
In particular, for the analysis of complex mixtures containing glucose, e.g. in honey, chromatographic methods such as high performance liquid chromatography and gas chromatography are often used in combination with mass spectrometry. Taking into account the isotope ratios, it is also possible to reliably detect honey adulteration by added sugars with these methods. Derivatization using silylation reagents is commonly used. Also, the proportions of di- and trisaccharides can be quantified.

In vivo analysis
Glucose uptake in cells of organisms is measured with 2-deoxy-D-glucose or fluorodeoxyglucose. (18F)fluorodeoxyglucose is used as a tracer in positron emission tomography in oncology and neurology, where it is by far the most commonly used diagnostic agent.

title: Glucose