Pascale Manoïlov

Claire Tardieu

Assessment of spoken interactions in two conditions: Teacher-tostudent versus student-to-student

, every form of interaction is situated and strongly depends on the individualities involved, each one speaking from their own universe but also permanently adjusting to their partner's discourse. When it comes to the assessment issue, and more specifically spoken interaction assessment, both Cambridge English and the Centre International d'Etudes Pédagogique (CIEP) exams and certifications include the student-to-student and examiner-student conditions whereas the Goethe-Institut and the Cervantes Institute, which are also exam providers, prefer the teacherto-student condition -the main argument for the latter being that the teacher's didactic/assessing positioning can better help the student to produce the best possible performance. The purpose of this research is to investigate which of the two conditions is preferable in terms of linguistic and pragmatic performance: teacher-to-learner or peer-topeer. Our hypotheses are the following: 1. Evidence of didactic/assessing positioning is not limited to language professionals but can be found in student-to-student interactions as well. 2. The teacher-to-learner condition is not necessarily more favourable to the student than the peer-to-peer one. This research will deal with the results of a micro experiment completed in 2013 in connection with the Département de l'Évaluation, de la Performance et de la Prospective (DEPP) at the French Ministry of Education in an assessment situation involving A1, A2, B1 students and teachers/evaluators in order to compare the performances of the students doing the same task under two conditions: first with a peer and then a teacher.

Introduction

This paper deals with the results of an experiment in the field of language assessment. It focuses on spoken interaction, a skill that was introduced in the French curriculum for secondary schools not that long ago (2005) in response to the publication of the Common European Framework of Reference for Languages (CEFR, Council of Europe 2001). The question raised here is the condition in which students are to be assessed when speaking with others. Two options are available:

• Condition 1: Student-to-student spoken interaction • Condition 2: Teacher-to-student spoken interaction. In French schools and for French national exams such as the 'Baccalauréat', Condition 2 is mostly preferred since teachers are considered the experts who are there to lead or scaffold the student's speech. However, for teachers who have to assess their pupils in regular class situations, such a pattern is time-consuming and as a result they often opt for Condition 1. Both the Cambridge English and the Centre International d'Etudes Pédagogique (CIEP) exams and certifications include the student-to-student and examiner-student conditions whereas the Goethe-Institut and the Cervantes Institute prefer the teacher-to-student condition -the main argument for the latter being that the teacher's didactic/assessing positioning can better help the student to produce the best possible performance. This research takes its roots in the elaboration of the protocol for the French testing called Cycle des Evaluations Disciplinaires Réalisées sur Echantillons (CEDRE), organised by the Département de l'Évaluation, de la Performance et de la Prospective (DEPP) at the French Ministry of Education. This CEDRE evaluation is performed every six years to assess the knowledge and skills of a large sample of French students. We will deal here with English which is one of the languages taught in secondary school. The participants we are interested in for this study are in their fourth year of secondary education and they are tested in five skills: oral and written comprehension and production as well as spoken interaction. For spoken interaction, the ministry has chosen Condition 2 to assess the students. However, this choice could be questionable since this is not the usual condition chosen by most teachers in normal class situations.

In order to investigate the appropriacy of using Condition 2 for spoken interaction, we organised an experiment to compare the two interactional patterns. Students were given a task to complete: they were provided with a touristic leaflet and had to decide with their partner (first a peer and then a teacher) how they would organise their weekend. The purpose of this research is to show which of the two conditions is preferable: teacher-to-learner or peer-topeer in terms of linguistic and pragmatic achievements.

Theoretical framework

According to the theory of the social mind and of sociocultural Second Language Acquisition (SLA) [START_REF] Lantolf | Socialcultural Theory and Second Language Learning[END_REF][START_REF] Lantolf | Sociocultural Theory and L2: State of the Art[END_REF], Léontiev 1981[START_REF] Swain | The Output Hypothesis and beyond: Mediating acquisition through collaborative dialogue[END_REF][START_REF] Wertsch | La médiation sémiotique de la vie mentale[END_REF], every form of interaction is situated and strongly depends on the individualities (personality, character, age) involved, each one speaking from their own universe but also permanently adjusting to their partner's discourse. We believe that both content and form in interactions depend not only on individualities but also on the social function as it is perceived by oneself and by the others.

Here we are relying on the notion of social function which is always a social fiction as Sartre puts it in L'Être et le Néant (1976) after observing a waiter at the Café de Flore. We also agree with [START_REF] Finkielkraut | Conversation sur notre temps avec Antoine Robitaille[END_REF] who stresses the different ways of behaving according to whether you are a waiter, a doctor or a teacher becoming 'second nature'. One may also refer to more recent studies on the topic: Social interaction is the very bedrock of social life. It is the primary medium through which cultures are transmitted, relationships are sustained, identities are affirmed, and social structures of all sorts are reproduced. [START_REF] Goodwin | Conversation analysis[END_REF][START_REF] Goodwin | Conversation analysis[END_REF]Clayman 2010:7) In our experiment, the participants are involved in a difficult task because they have to take up roles that are close to real life experience (CEFR 2001:121) -the students have to act as teenagers on a visit to an English speaking country who want to organise their weekend. The teacher's role consists of becoming a host family member who will organise the weekend with the student. When engaged in task-based interaction, participants are expected to behave in a certain way and to produce a certain type of discourse as required by the specific assessment purposes (both in terms of linguistic and pragmatic criteria). They are indeed supposed to ignore the institutional context and their actual social role as students or teacher and feel free to express their likes/dislikes or even modify their true personality. We therefore assume that the interaction will depend on their greater or lesser readiness to fit the roles assigned by the task. In order to analyse the results according to the participants' positioning in the spoken interaction, we intend to transfer Clot's concept of 'clinical activity' [START_REF] Clot | Genres et styles en analyse du travail. Concepts et méthodes[END_REF]. Although this framework was originally meant for any work situation, we believe that its methodological approach fits the study of the activity that takes place in the language class. This conceptual tool will enable us to measure the gap between the completion of the task as planned by the designer and the actual activity of the participants, i.e. what really happened.

Our first hypothesis is that the gap between the planned task (what is expected in terms of language and interactional patterns from the teacher) and reality (what learners actually produce) is narrower in Condition 1 (student-to-student) than in Condition 2 (teacherto-student).

Our second hypothesis is that the wider gap in Condition 2 is due to the teacher's didactic positioning whose social role would overcome the one assigned by the task. In other words, the teacher who is supposed to play the role of a host family member would have difficulties in leaving aside the assessor's position.

Finally, our third hypothesis is that each condition will have an impact on the student's performance both in terms of pragmatic and linguistic behaviour.

The protocol

Our experiment was conducted in February 2014 in three different secondary schools in Paris suburbs. Twelve 14/15 year-old students (A2+/B1 levels) and their three teachers were videorecorded while performing a spoken interaction task in the two conditions. The task was a role-play which slightly differed according to who the students were interacting with. In both conditions, the participants were provided with a leaflet that displayed the pictures and the names of some famous tourist attractions either in London or in New York.

The protocol was as follows:

Step 1 -Spoken interaction task to be performed in Condition 1 (student-to-student): the students were told they were both staying in a host family in a foreign city (London or New York). Their goal was to discuss and agree on the organisation of the following weekend.

Step 2 -Spoken interaction task to be performed in Condition 2 (teacher-to-student): the students were told they were staying in a host family in a foreign city (London or New York, depending on which city had been chosen in Condition 1). The teacher was asked to play the role of the host family mother (all the teachers were female). The two participants had to discuss and agree on the organisation of the following weekend.

In both conditions, the instructions were to make suggestions, to react to suggestions and to reach an agreement on the organisation of the activities of the weekend. The conversations were due to last no less than three minutes and no more than five minutes. The 18 spoken interactions were video-recorded in a classroom according to the following order:

• student 1 with student 2 • student 1 with teacher • student 2 with teacher.

Before the peer-to-peer interaction, it was made clear to the students that the video recordings would be used for two purposes: the first one for assessment by their teacher and the second one for research purposes. In Condition 1 (student to student), only the researcher stayed in the classroom (to monitor the video camera) and the teacher waited outside. The students were perfectly aware assessment was involved in both conditions.

After each dialogue with the teacher (Condition 2), the latter was asked to assess the student according to the grid design by the DEPP. In order to evaluate the students' performance in Condition 1, the same teacher watched the videos of the spoken interaction in the peer-to-peer situation. The same grid was used. The grid is divided into two parts: the first one deals with the pragmatic skills and the degree of achievement of the task (from 1 to 5 that is from the minimum to the maximum fulfilling of the task). The second part assesses the linguistic skills i.e. lexical variety, grammatical and phonological accuracy from A (the lowest) to E (the highest), the final grade being thus a combination of a number and a letter). The grid itself was elaborated by a group of language experts (in English, German and Spanish) relying on both the CEFR (Council of Europe, 2001) and the French language curriculum. At the end of the experiment, the students were asked to complete a questionnaire and were interviewed to ascertain their feelings regarding the experiment and their preference for one condition or the other. The questions were as follows: 1. Do you like English? 2. Did you like taking part in the experiment? 3. Who did you prefer performing the task with -your fellow student or your teacher? Which condition was most favourable to you?

The videos of the spoken interactions (amounting to 1 hour and 35 minutes) were transcribed on CLAN software [START_REF] Macwhinney | The CHILDES project: Tools for analysing talk[END_REF] which allows for text and video alignment as well as for some automatic data processing. According to grounded theory [START_REF] Strauss | Basics of qualitative research: grounded theory procedures and techniques[END_REF]), our coding system was data-driven and allowed for quantitative and qualitative analysis.

Analysis

When designing a task for students to develop their spoken interaction skills, the teacher always thinks ahead and has some specific expectations that would match his/her learning goals. The process is the same when designing a test because the assessor intends to check the knowledge and skills that were acquired by the learners. Some instructions are given to the participants so as to trigger the use of specific language functions. This is what is considered as the planned task and it usually reflects the assessor's goals.

Here are the instructions (in italics) given to the participants followed by the language functions that could be expected. We used the functions listed in the Threshold Level (Council of Europe 1990): The aim of our analysis is to compare which functions were used by students and teachers to complete the task. Since one of our hypotheses is that the gap between the task and the activity is wider in Condition 2 than in Condition 1, we will study the patterns of interaction which emerge from each situation. This should allow for the analysis of the speakers' positioning.

Quantitative analysis

The close study of our data led us to investigate three aspects of the discourse that appeared to be relevant to measure the participants' positioning in the interaction:

1. The number of words uttered by each speaker would give us some information on who takes the floor in an exchange. 2. The use of subject pronouns ('I, you and we') to highlight who talks about whom. These pronouns are potentially a good indicator of the intersubjective positioning of the participants in the task. 3. The number of questions formulated by each participant. The goal of the task was to come to an agreement and therefore, it seems reasonable to think that requesting information or preferences would display a certain positioning in the conversation process.

In order to draw conclusions on comparable data, all the quantitative measures were made on the first 3 minutes 20 seconds of each dialogue since it was the length of the shortest conversation. Interestingly enough, the conversations among students were longer on average than the conversations in which a teacher was involved. The teachers were following a question/answer pattern which gave the conversation a quicker rhythm and did not really allow for pauses more frequently noticed in peer to peer conversations.

Who is the most talkative?

The students who took part in our experiment were A2+/B1 (CEFR 2001). This means a difference in terms of fluency between the teacher and the learner with the former uttering more words per minute than the latter. This raises the question of who talks the most in a situation where the student is assessed by a teacher who is acting in the role-play. In Condition 2, are the teachers/assessors able to stick to their role (the role assigned by the language task in which they were meant to play one of the host family members) and does this role play enable the student to complete the task according to the task designer's expectations?

The following tables show the number of words uttered by each participant in Conditions 1 and 2.

Table 1 Number of words uttered by each participant in Condition 1 Table 2 Number of words uttered by each participant in Condition 2

In Condition 1, the dialogues between peers show an unbalanced number of uttered words with the more able students being more talkative than the less able ones. However this difference is not a major one and can be explained by the roles assumed by some students who were confronted by their less able peers and who needed to provide vocabulary, to reformulate or to scaffold their partner's speech. When in conversation with the teachers (Condition 2), the difference becomes wider for the less skilled speakers. These students explained that they did not feel confident and did not dare talking and uttered a minimum number of words because they feared the teacher's reaction to their potential errors. As far as more competent learners are concerned, the number of words uttered by each speaker is usually better balanced. The proportions observed in Condition 1 were confirmed and amplified in Condition 2 with less able learners speaking even less with the teacher than with their peer.

There is one exception to this trend: one of the students (MOH) working in Condition 2 completely took the lead in the conversation which turned out to be more a monologue than a dialogue. He never looked at the teacher and was therefore unable to consider her reactions or nonverbal feedback. The teacher let the student speak without interrupting (and without really being able to interrupt) which resulted in an unbalanced exchange until the learner ran short of ideas. During the interview this pupil mentioned that he felt more comfortable with a peer than with the teacher. This position is confirmed by the dialogue in Condition 1, which is well balanced in terms of numbers of uttered words (MOH-NAR).

These data show that even if the teachers tend to speak more than the students, this does not necessarily mean that the learners are disadvantaged. In other words, they do not speak less than with peers. It is only the difference between the two speakers that is bigger in Condition 2 but not the amount of learner speech. If we go back to the core of our subjectassessment -we may wonder how these unbalanced dialogues influence the teacher's perception when evaluating the students. Before examining the results of the assessment proper, we would like to focus on the reason why teachers tend to talk more than students. Does this mean that in Condition 2, the lead is on the teacher's side? More data might help us answer this question.

Who talks about whom?

One of the prominent characteristics that we discovered in the dialogues among the participants is the differential use of subject pronouns. These referential markers could potentially highlight how the participants position themselves in the dialogue and in the completion of the task.

Table 3 deals with the dialogues in Condition 1. We added the number of subject pronouns used by the 12 students in the course of their 6 spoken interactions. In Table 4, the number of conversations that we took into account doubled since each of the 12 students had a conversation with a teacher (Condition 2). The difference in the number of pronouns used in Condition 1 (N=159) and in Condition 2 (N=432) is due to the number of dialogues that we analysed (6 vs 12) therefore we shall only look at percentages. However, it is important to mention that there was also a difference in the structure and length of utterances produced in each condition. In condition 1, what the students utter is often limited to incomplete sentences such as 'when?', 'on Monday', 'oh no Saturday', 'ah ok' whereas the conversations with the teachers are more elaborate. The latter would ask complete questions and require full answers. When the student did not provide a full answer, then the teacher usually reformulated it.

In Condition 1, the use of the pronoun 'I' (49%) shows that half the utterances are self-referential. Students talk about themselves, they express what they like or what they do not like, what they wish to do, their preference and finally their agreement or disagreement with their partner's suggestion. However, they also take into account their partner's point of view when they enquire about the other's desires, likes or preferences hence the use of 'you' (32%) as in 'Where do you want to go next weekend?'. The pronoun is also used because the speaker seeks information as in 'Do you know the MOMA?' therefore the interaction makes sense since the students collaborate in trying to know a thing or a fact (Council of Europe 1990). We can also notice that, to a lesser extent, students use 'we' in their dialogues. This demonstrates how the speakers engage in the task: the organisation of the weekend is meant to be a co-construction in which the role assigned by the fictional situation predominates. The participants were asked to come to an agreement therefore, having expressed their own point of view, they show that they reach an agreement in referring to the two of them as in 'and we will go shopping at Macy's because we have money and we want to spend money.' These 'we' are mostly found in the second part of the dialogues. As mentioned before, we only used the first 3 minutes and 20 seconds of each dialogue, therefore, for the longer ones, these pronouns do not appear in our analysis. Thus, it is likely that our figures underestimate the copositioning of the participants since it appears that the 'I' and 'you' pronouns progressively change into 'we'. The dialogicality (Du Bois 2007) of their speech i.e. the interactional structure of the language reflects the enaction of their personal and social relationships with one another (Halliday and Matthiessen 2004).

In Condition 2, the use of the subject pronouns differs quite substantially. Whilst the students continue to predominantly use 'I' (36%), the teachers, who play the role of the host family member, only use it in 4% of all cases. Conversely, they mostly use 'you' (43%) in the conversations as opposed to students who only employ it in 3% of all sentences. This distribution reflects two important aspects of the type of relation that is built up between each pair. First, this shows that the conversation is clearly led by the teachers who tend to ask questions (the types and functions of these questions will be discussed later) to the students about their wants and desires, likes and dislikes or preferences but also on their knowledge of the possible places of interest to be explored. The whole range of questions that teachers generally use when addressing students and prompting them to develop their speech is displayed such as 'What would you like to visit?', 'When would you like to go?', 'Are you interested in art?', 'Where would you like to have lunch?'. Therefore, it is often the teachers who initiate the topics and suggest possible options. The students tend to respond to suggestions without almost ever offering or suggesting choices.

Second, the instructions given to the participants pointed out that they should enquire about the co-speakers' wants and desires but they also mentioned making and reacting to suggestions. The very small amount of 'I' pronouns used by the teachers and 'you' pronouns used by the students suggests that the dialogue serves as a task in which the pupils' speech is driven and supported by the adult. The interaction appears as highly unequal in terms of coconstruction: the teachers talk about the students who in turn, only talk about themselves. If the latter seems to be able to stick to the role assigned by the task, the former tends to be caught up by their social role. Condition 2 favours an unequal positioning in the sense that the role-play is more difficult for the teachers who tend to play their actual social role rather than their fictional persona. The task involved a discussion on equal grounds (as far as the relationship between two teenagers could equal that of a student and a host-family parent) but the disproportion between the use of subject pronouns suggests an unbalanced relationship. This view is supported by the very low amount of 'we': 4% by the students and 9% by the teachers in condition 2 as opposed to 19% in Condition 1. In Condition 2, the task is clearly not a 'team' construction as opposed to Condition 1 where the students tend to come to a coconstructed agreement based on shared points of view rather than a one-way spoken composition. This corroborates our hypothesis that the gap between the expectations raised by the task design and reality is wider in Condition 2 than in Condition 1.

Who asks questions and how many?

Another striking difference between the two conditions was the use of questions. The design of the task implied that the participants would enquire about their partners' likes or dislikes, wants and desires or preferences. Seeking information was also part of it. Therefore questions were expected in the participants' discourse but their number greatly differed from one condition to the other as shown in Tables 5 and6. In Condition 1 (Table 5), the number of questions asked by the students is evenly shared and ranges from 3 to 10 over a period of 3 minutes 20 seconds. The participants share an equal status and no one seeks to take a leading role. However, in Condition 2 (Table 6), the pattern of the dialogue changed considerably with teachers asking between seven to twenty times more questions than students. The teachers were supposed to play a role in which they engaged in a discussion but the dialogue often took the form of an interview rather than a conversation. One pair (TCH-MOH), once again, appears to be an exception for the reason mentioned before. MOH decided to engage in a monologue and stated all his desires and wants for the organisation of the weekend. As the teacher was not able to speak much, she obviously did not ask many questions. For all the other dialogues, it seems that the teachers were willing to help the learners. The guidance offered by them was made in the form of questions as teachers would usually do. Therefore it appears that, once again, the dialogues in Condition 2 display an unbalanced structure in the exchange that accounts for and replicates the type of hierarchical relationship found in the classroom. As Goffman argued, 'the syntax of interaction (…) is the place where face, self, and identity are expressed, and where they are also ratified or undermined by the conduct of others' (in Heritage and Clayman 2010:9). The linguistic and pragmatic choices made by the teachers had thus an impact on the shaping of the participants' role and on their positioning in the interaction. These conclusions, and more specifically the status of questions, require a more detailed qualitative analysis so as to understand the positioning of each participant in the interactions according to Conditions 1 and 2.

Qualitative analysis

As they completed the task, the participants came to express their communicative intentions through a certain number of language functions (now LF) that we classified. We used and adapted the typology of the Threshold Level, now B1 in the CEFR (Council of Europe 1990). These LF were not evenly used by the students or the teachers and the underlying purpose behind some of them also appeared to be different. In Condition 1, the learners resorted to all the above LF to complete the task. They did not often correct their partners but it was not a requirement. Therefore the actual spoken activity displayed by the students is in line with what was expected in planning the task.

Conversely, in Condition 2, not all LF were found. In accordance with what was revealed by the use of subject pronouns, the teachers hardly ever expressed their own wants and desires, their preference or their likes and dislikes. They mostly enquired about what the students thought although the task implied sharing opinions on the subject to come to an agreement. In doing so, they positioned themselves not as co-organisers but as experts in charge of guiding a learner. As Jaffe puts it:

[a] speaker positionality is built into the act of communication. … By taking up a position, individuals automatically invoke a constellation of associated social identities. In doing so, speakers project, assign, propose, constrain, define, or otherwise shape the subject positions of their interlocutors. … An utterance framed as a performance, for example, positions receivers as an audience; a speaker who takes up an expert stance to give advice positions receivers as novices (2009:3-8) [our emphasis] This hierarchical position is also reinforced when teachers correct students even though the errors do not create a communication breakdown (Manoïlov 2010). It should be noted that the teachers were specifically required not to correct students because the completion of the task (a role play) did not require such discourse moves.

Example 1 30 ADE: uh I'd like to go to Time Square too. 31 TCH3: yes why? 32 ADE: uh because I was told there are big screens, large screens and uh with ad. 34 TCH3: ads yes, yes.

In line 34, the reformulation shows that the adult clearly goes back to her institutional role, that of a teacher, since this move does not add anything to the completion of the task. This aspect is even more obvious in the meta-functions of the questions asked in the dialogues. On the one hand, they had a communicative purpose which was task oriented (example 2) but in some cases they were clearly pedagogical (example 3).

The following example is an extract from an interaction between two students who resort to questioning. The two questions asked by SON (lines 60 and 62) are task-oriented. In line 60, she is interested in the organisation of the weekend and asks her partner about the planned schedule (LF10). She has to repeat her question (line 62) because her partner did not understand it.

When MOR asks a question (line 66) because she does not know what the MOMA is, she is genuinely enquiring for information (LF13). Seeking information has a communicative function. The whole extract shows that the two students are working towards the completion of the task. The process is a collaborative one, each participant being equally part of the coconstruction.

However in Condition 2, some questions had a different intent when they were uttered by a teacher. In line 38, the teacher's question could be understood as a suggestion but in line 39, she adds 'what do you know?'. Once again we could consider the question as an enquiry to find out information about Times Square but the third move (line 41) clearly displays the teacher's intention. She wants to find out whether the student knows about Times Square not because she is herself ignorant but because she wants to prompt the learner to display her knowledge. Therefore the question turns out to be a didactic one or what we call a 'quiz question'.

LF 12 (Correcting) and LF 13 (Imparting/Enquiring about factual information) were always task-oriented when used by the students. However when used in Condition 2 by the teachers, LF 12 and LF 13 were sometimes task-oriented and sometimes didactic questions. LF 222 (Enquiring whether one know or does not know a thing or a fact) and LF 223 (Asking for justification) were always used by the students with a communicative intent and always used by the teachers with a didactic intention. Therefore we can see that it was sometimes difficult for the teachers to play the role assigned by the task and to forget for a moment their teacher's status. This has an impact on the relationships in the interaction. When interviewed, some of the students mentioned that they were impressed and they did not always feel as confident as when they were talking with a peer. However, this feeling is not shared by all the students. Four of them (one third) declared that they preferred interacting with the teacher who was reassuring. They appreciated the fact that the expert was there to support them. We can then suppose that there is a correlation between the students' preferring Condition 2 and their own positioning more or less in line with the social role assigned by the task or the one assigned by the institution. In other words, Condition 2 is preferred by students who remain students no matter what.

We shall now turn to the results of the assessments to check if the previous findings had an impact on the teacher's appraisal of the students' performance.

Results of the assessments: What they tell us

As mentioned before, this experiment was meant to test the conditions in which students could be assessed on their spoken interaction skills. One of our goals was to seek whether one condition would be more favourable to the students than the other. The teachers were asked to evaluate them using the grid designed by the DEPP. The teachers first assessed the students' performance in Condition 2 immediately after their interaction with them. They were then asked to watch the video that had previously been recorded with two students completing the task and, they used the same grid to evaluate them in Condition 1. The grade is composed of two items, the figure concerns the pragmatic skills and the degree of achievement of the task (grade 1: minimum, to grade 4: maximum), and the letter concerns the linguistic skills (grade A: minimum, to grade E: maximum). In the grid, the range of grades for the linguistic skills is wider than the pragmatic skills because it was found that for practical purposes, it would help to have a more detailed description. The hatched boxes represent the best grade obtained by each participant. In eight cases out of the 12, the students were given a better grade in Condition 1 than in Condition 2 (66%). The teachers were often pleasantly surprised by the way the students were able to engage in the conversation to complete the task in peer-to-peer interaction. They initiated a lot of interactions, they reacted to their partners' suggestions, they launched new topics, they asked about new information, they organised the weekend in a very efficient manner so as to complete the task. Conversely, when in conversation with the teachers, they were keener on answering suggestions or questions without initiating any new topics. They followed the teacher's guidelines thus positioning themselves as students and not really as partners in the task completion. This position, which was implicitly imposed by the social identities at stake in the interaction, certainly had an impact on the grading. If we look closely at the results, we can notice that it is almost always the pragmatic grade (i.e. the number) that is better in Condition 1 than in Condition 2. The linguistic one (i.e. the letter) remains the same in both conditions except for one student (JUL) who was deemed more skilled when in interaction with the teacher. This figure evaluated the ability to complete the task and the ability to interact in an efficient manner. It seems that the teacher considered that the communication between the students was more successful and productive when in Condition 1. The equal status enabled and led the students to be more active in the way they engaged in the conversation and in the task. The asymmetrical relationship in Condition 2 led to an unbalanced structured-conversation where the teachers initiated topics through questions which the students answered. Their role was therefore more passive and this could explain the difference between the two grades. However, when in conversation with the teacher some students did better in terms of linguistic skills. This could be explained by the fact that students would concentrate more on the language forms when in interaction with the teacher because they know that teachers usually value this aspect of the language more.

Answering our hypotheses

Hypothesis 1: In the context of spoken interaction, the gap is bigger between the task planned and the activity observed in Condition 1 (TCH-STU) than in Condition 2 (STU-STU)

The qualitative analysis of the language functions displayed in the participants' speech shows that in Condition 1 there is little difference between what was expected and the actual activity. However, in Condition 2, the gap is bigger because the teachers did not fully adopt their imaginary roles. Their speech was often dedicated to guide the students and they were not involved in opinion sharing. We must point to the fact that the teachers' role was a difficult one that may have biased their production. The creation of roles that would be realistic implies that what the teachers and the students were expected to play was similar but not identical. This should be kept in mind.

Hypothesis 2: The main reason for this discrepancy lies in the positioning of the speakers, more or less in line with the social role imposed by the task or the social role imposed by the school context Our analysis showed that the teachers tend to hold the floor when in conversation with the students, especially the less able ones. The former also oriented the conversation towards the learner in using the second person subject pronoun and in asking a tremendous amount of questions. The unbalanced structure of the dialogue reflects the unequal status between students and teachers that the social fiction imposed by the task is unable to erase. The social function remains strongly significant.

Hypothesis 3: The positioning of the speakers has an influence on their performances

The results of the assessments show that 8 students out of 12 were better evaluated by the teachers in Condition 1 than in Condition 2. When in interaction with the expert (i.e. the teacher) their status of learner was more obvious and they behaved in a different manner. The social positioning influenced the pragmatic behaviour of the participants which in turn had in impact on the grades. The teachers found the students more efficient when interacting with their peers than with them probably because, in Condition 2, the students took less initiative, asked less questions and were not actively involved.

Yet not all students behaved the same in Condition 2. In the interviews we conducted at the end of the experiment in order to ask the students which condition they preferred, their answers were in keeping with the attitudes displayed during the spoken interactions. Interestingly, the students can be placed on a continuum according to their greater or lesser dependency on the teacher as displayed in Table 8.

Table 8 The institutional-social continuum

One more proficient student (ANA) performs better with her teacher and clearly prefers this condition because she can draw the best from it. Another more proficient student (JUL) clearly states that scaffolding from the teacher is unfair and introduces a bias in the assessment. She is the most autonomous student. According to her the difference between her language skills and the teachers' in Condition 2 disadvantages students. Most students (9 out of 12) acknowledge the importance of scaffolding (provided by the teacher even in an assessment situation) although they prefer interacting with a peer and very often succeed better in this condition.

Conclusion

Our study suggests that Condition 1 seems more favourable to students than Condition 2 especially when they feel more comfortable with a peer than with a teacher.

When the task was chosen, the designers' intention was to erase or at least reduce the hierarchical relation that usually exists between a teacher and a student. While in the process of playing their assigned role the participants were meant to perform an ordinary conversation, it appeared that Condition 2 rather favoured institutional talk to the disadvantage of 66% of them (Heritage and Clayman 2010). Thus, it seems that the interactional roles are all the more reinforced by the institutional context which is a source of asymmetrical positioning even before any action is taken or any word is uttered by the participants. Our study shows that when engaged in dyads with students in an interactive assessment task, the teachers' position remains high. This is not only because of their mastery of the language but also because of their social function as teachers that is deeply anchored in them within the institutional context. We also found that the places are collaboratively constructed in Condition 1 enabling the students to position themselves as equals in the conversation, whereas they seem to be imposed upon by the social context in Condition 2 where the teachers keep their dominant position. Although our experiment relies on a limited corpus and as such cannot prove to be generalisable, it tends to show that even with basic or independent language users (Levels A2-B1) the most favourable assessment condition for oral interaction is peer-to-peer. A larger scale study is now planned to check these results and to take more precisely into account the proficiency levels of the participants. Indeed, it seems necessary to vary the level of each pair with more competent students interacting with less competent ones or pairs of students of equal competence. This study should have consequences not only for the way French teachers evaluate their students but also on the way they teach interactive skills both on a pragmatic and linguistic level.

  At the end of the conversation, you should agree with your friend about your plans for next weekend.

	Where would you like to go? What would you like to see or do?
	Enquiring about/Expressing wants, desires
	Enquiring about/Giving factual information
	Make some suggestions
	Suggesting a course of action
	React to your friend's suggestions
	Enquiring about/Expressing like -dislike
	Enquiring about/Expressing preference
	Agreeing / Disagreeing

Table 3 Total number of subject pronouns used by the participants in Condition 1

 3

	STU-STU
	I	YOU	WE
	78	51	30
	(49%)	(32%)	(19%)

Table 4 Total number of subject pronouns used by the participants in Condition 2

 4

	STU			TCH
	I	YOU	WE	I	YOU	WE
	152	15	18	19	187	41
	(36%)	(3%)	(4%)	(4%)	(43%)	(9%)

Table 5 Number of questions asked by the participants in Condition 1

 5

		STU 1 STU 2
	BIL-VEN	9	10
	MOH-NAR 9	7
	JUL-MAT	2	3
	SON-MOR 3	4
	ADE-ANA	4	6
	SAL-NIC	3	5

Table 6 Number of questions asked by the participants in Condition 2

 6

	TCH STU

Table 7 Grades assigned by the teachers according to Condition 1 and Condition 2

 7

		Condition 1	Condition 2
		STU--STU	STU--TCH
	NAR 4C	3C
	MOH 4C	3C
	TCH1
	BIL	3D	4D
	VEN 4C	3C
	MAT 4D	3D
	JUL	4D	4E
	TCH2
	SON	4E	3D
	MOR 4D	3C
	ANA 3C	4D
	ADE 3C	4D
	TCH3
	SAL	4D	3C
	NIC	4D	3C


Olivier Petit

Franck-Dominique Vivien

When economists and ecologists meet on Ecological Economics: two science paths around two interdisciplinary concepts

 that is a marker in the field of ecological economics. What unites these two authors is a manifest interest in the work coming out of systems analysis in the 1970s -as we shall see, that interest ultimately led to fairly contrasting visions of the field of ecological economics.

Introduction

Nearly thirty years after the creation of ecological economics, it seems fitting to review its achievements conceptually and also in view of the objectives that were assigned to it at its creation. Ecological economics essentially grew out of economists working in the environmental field and growing dissatisfied with the way that standard economics saw interactions between nature and societies and ecologists anxious to take human activities (including economic) into account in a much more direct way, within the dynamic of the ecosystems on which they depend. This clearly inscribed the new field of ecological economics within an interdisciplinary and even transdisciplinary perspective, as is emphasized by the subtitle of the journal Ecological Economics, created in 1989. Today, what remains of the original aspirations? How has the "encounter" between economy and ecology unfolded, and what has this encounter led to? Answering this question exhaustively would no doubt require telling the story of the individual paths of thousands of researchers involved in collaborative research operations, which would no doubt highlight the uniqueness of each of these paths and would be difficult to reduce to broad typologies. In order to try to provide some thoughts on the evolution of this trend and the relationship between economists and ecologists, we have chosen to focus on two items2 that are undoubtedly among the achievements of ecological economics, although their mobilization is far from uniform among the authors who make use of them: coevolution and ecosystem services. The literature mobilizing these two concepts within ecological economics is quite extensive, which is why we have chosen to study each of these subjects through the path of two authors who were among those at the beginning of the ecological economics trend and whose names are generally associated with both of these subjects: Richard B. Norgaard, whose work on the coevolutionary paradigm [START_REF] Norgaard | Development betrayed: The End of Progress and a Co-Evolutionary Revisioning of the Future[END_REF]) is recognized as one of the foundations of ecological economics [START_REF] Munda | Environmental Economics, Ecological Economics, and the Concept of Sustainable Development[END_REF]; Robert Costanza, who initiated work on the monetary valuation of ecosystem services [START_REF] Costanza | The value of the world's ecosystem services and natural capital[END_REF] that is a marker in the field of ecological economics. Moreover, exploring the encounter between economists and ecologists through these two figures seems relevant to us, since the first made the journey in one direction (from economy to ecology), while the other kind of took the opposite path (from ecology to economy). What unites these two authors is a manifest interest in the work coming out of systems analysis in the 1970s -as we shall see, that interest ultimately led to fairly contrasting visions of the field of ecological economics. in 1971), he nevertheless felt early on the need for a dialogue on economy and ecology that would have an interdisciplinary perspective. This commitment was a legacy of complex thought and systems analysis, two fields that, during a large part of his career, he applied to the notion of coevolution. Before discussing how this author has mobilized the notion of coevolution, let us look at his original methodological and epistemological positioning, which led him to consider an interdisciplinary dialogue between economists and ecologists.

Richard B. Norgaard and the concept of coevolution

2.1.A plea for methodological pluralism

Richard B. Norgaard is known, within the field of ecological economics, to have emphasized the need to adopt methodological pluralism [START_REF] Norgaard | The case for methodological pluralism[END_REF]) -this position is also often recognized as one of the foundations this trend [START_REF] Gowdy | The approach of ecological economics[END_REF][START_REF] Lo | The Problem of Methodological Pluralism in Ecological Economics[END_REF], even if some authors, like Clive [START_REF] Spash | New foundations for ecological economics[END_REF], believe that methodological pluralism harms ecological economics more than it serves it. [START_REF] Norgaard | Epistemology: Methodological Pluralism in Theory and Practice[END_REF] recognizes first of all that the disciplines of economics and ecology are far from unified. Each is criss-crossed by various trends that use very different languages, and communication between these different trends is often complicated and would be so even if they were to use similar terminology. In fact, behind an apparent disciplinary homogeneity, in reality, a struggle for values and world views, which are difficult to reconcile, is being played out. But, according to Norgaard (1994: 96), "[m]ost people, including scientists, still believe that our multiple ways of understanding different aspects of ecosystems can be merged into one coherent view". In such a context, the idea of achieving a unified vision of the relationship between economy and ecology, in a new field -ecological economics -may seem illusory. Ecological economics can therefore be marked out as a field of mutual understanding of different visions and values that run through these two disciplines. This new field of experimentation can thus be defined as "an effort to hasten a particular merger by pushing ecological understanding towards economics, and economic understanding towards ecology" (Norgaard, 2003:1). Thus, Norgaard considers coevolution to be a concept that allows us to think about the relationship between economy and ecologythat is, a border concept.

2.2.Is the coevolutionary paradigm the foundation of ecological economics?

The term coevolution was introduced in the early 1960s in the field of biology, following an article by Paul Ehrlich and Peter Raven entitled "Butterflies and Plants: A Study in Coevolution" [START_REF] Ehrlich | Butterflies and Plants: A Study in Coevolution[END_REF]. The concept of coevolution was mobilized to describe a genetic change in a species in response to the evolution of another species. Thus, strictly speaking, coevolution indicates the evolution of two populations that have internal diversity and interact so that they influence the selection environment of each other, so that their evolutionary trajectories are coupled [START_REF] Van Den Bergh | Evolutionary thinking in environmental economics[END_REF]. Gradually, this concept has been expanded to denote different forms of coevolutionary interactions between species or between genes. More recently, the concept has been applied to a group of types of interaction between genetic changes and cultural changes within the human species, in particular. The metaphorical use of coevolution has enabled its use later in fields as diverse as technical change and socioeconomic issues [START_REF] Rammel | Managing complex adaptive systems -A co-evolutionary perspective on natural resource management[END_REF].

In the late 1970s, Richard B. Norgaard looked at coevolution as a means of understanding the relationships that develop between natural systems and social systems, particularly through the dynamics of environmental and social change. Initially, Norgaard mobilized this concept following a mission on the management of the Amazon area which he undertook in the 1970s with the Brazilian government [START_REF] Norgaard | Sociosystem and Ecosystem Coevolution in the Amazon[END_REF]. Strongly influenced by systems analysis (through the work of Boulding, in particular), he borrowed the term coevolution from [START_REF] Ehrlich | Butterflies and Plants: A Study in Coevolution[END_REF], although curiously, he does not refer to their article in his early work 3 . He takes up this notion for his own purposes, applying it to social systems and ecosystems. He illustrates, through the agricultural issue, that far from evolving independently of each other, ecosystems and human societies co-operate, that is, their evolutionary paths influence each other. In fact, just as in the field of biology, there is a constant interaction between organisms and their environment (the organisms are not just the result, but they are also the cause of their own environment), there is a constant interaction between ecosystems and societies. More precisely, Norgaard (1994:40-41) indicates : " … social and environmental systems coevolve such that environmental systems reflect the characteristics of social systemstheir knowledge, values, social organization, and technologieswhile social systems reflect the characteristics of environmental systemstheir mix of species, rates of productivity, spatial and temporal variation, and resilience. The coevolutionary description of development explains why, and to some extent how, everything is related to everything else". To the extent that evolution, in the Darwinian sense of the word, engages the three processes of variation, inheritance, and selection [START_REF] Kallis | Coevolutionary Ecological Economics[END_REF], these three processes are also found in the idea of coevolution of environmental and social systems. As stressed by Norgaard (1994: 41): "People survive to a large extent as members of groups. Group success depends on culture: the system of values, beliefs, artifacts, and art forms which sustain social organisation and rationalise action. Values and beliefs which fit the ecosystem survive and multiply; less fit ones eventually disappear. And thus cultural traits are selected much like genetic traits. At the same time, cultural values and beliefs influence how people interact with their ecosystem and apply selective pressure on species. Not only have people and their environment coevolved, but social systems and environmental systems have coevolved". Let us recall that two systems coevolve when at least one of the systems is evolving and influences the other system [START_REF] Norgaard | Environmental Economics: An Evolutionary Critique and a Plea for Pluralism[END_REF].

It was by analysing the set of conventions governing the idea of development, from a Western perspective, that the idea of coevolution was born [START_REF] Norgaard | Coevolutionary Contradictions: Prospects for A Research Programme on Social and Environmental Change[END_REF]. According to Norgaard, five conventions guide development models in Western thought: atomicism (also called reductionism, but in a pejorative sense), mechanism (a vision of a clock-like world where it is possible to accurately predict the paths of certain objects), universalism (the idea that everything can be explained, at any time and any place, with the use of a limited number of scientific laws), objectivism (which leads to analysis of phenomena by keeping them at arm's length, as if the analyst had no control over them), and monism (the idea that our different ways of seeing the world can ultimately be synthesized in a consistent manner). With this analysis grid in mind, it became possible for R.B. Norgaard to reread the development of the Brazilian Amazon, shaped by these influences and by the idea of progress that underlies it, and to propose, conversely, a radically different vision of development that can be summed up in the idea of coevolutionary development. Coevolutionary development thus appears as a paradigmatic vision of the relationship between human societies and ecosystems. The coevolutionary development process is therefore built from the interaction between the five dimensions that [START_REF] Norgaard | Development betrayed: The End of Progress and a Co-Evolutionary Revisioning of the Future[END_REF] identifies as important: values, technology, environment, organization, and knowledge. These interactions are by nature dynamic and non-deterministicthus unpredictable. Moreover, Norgaard attaches particular importance to distinguishing this approach from the A -M (Atomistic-Mechanistic) vision that he associates with the development approach in the field of environmental economics and natural resources [START_REF] Norgaard | Environmental Economics: An Evolutionary Critique and a Plea for Pluralism[END_REF].

The concept of coevolution was recognized very early on as a key concept in defining the scope of the field of ecological economics [START_REF] Gowdy | Coevolutionary Economics: The Economy, Society and the Environment[END_REF][START_REF] Spash | The Development of Environmental Thinking in Economics[END_REF], and even as a unifying theme, a paradigm [START_REF] Munda | Environmental Economics, Ecological Economics, and the Concept of Sustainable Development[END_REF]. According to Spash (1999:425) : "Evolutionary dynamics are an important aspect of ecological economics which emphasise that economic and environmental systems are interacting and changing, often unpredictably, rather than static, and this implies analysing non-deterministic processes rather than optimal paths to static equilibria. However, the particular interpretation via the coevolutionary paradigm remains a topic for open debate within ecological economics".

However, it is important to acknowledge that with the exception of a limited number of authors (John Gowdy, Giorgos Kallis, Richard Norgaard, Christian Rammel), coevolution has not really been a distinguishing feature recognized as a unifying idea by proponents of ecological economics. Recent work [START_REF] Rammel | Managing complex adaptive systems -A co-evolutionary perspective on natural resource management[END_REF][START_REF] Kallis | Coevolutionary Ecological Economics[END_REF], however, offers some interesting paths allowing us to take stock and sketch out future developments for a research program based on the notion of coevolution in the field of ecological economics.

It is difficult to describe coevolution as a subject, in light of the various ways in which the term is used. At different times, Norgaard himself uses it to talk about the coevolution and the coevolutionary development of a model (1985), a paradigm (1984), a concept (1985), and even a metaphor.

When Norgaard addresses coevolutionary development as a paradigm, he generally opposes the mechanistic-atomistic Newtonian paradigm that is often used in the field of environmental economics and natural resources [START_REF] Norgaard | Environmental Economics: An Evolutionary Critique and a Plea for Pluralism[END_REF].

The status of coevolution in the work of Norgaard must be understood in light of the interest that he had in metaphors in the scientific field. Biological metaphors and analogies have abounded in the area of economic analysis since at least the eighteenth century4 . Consequently, it is not surprising that ecological economy has grown by espousing this view, from the 'cowboy economy' of [START_REF] Boulding | The economics of the coming spaceship earth[END_REF], by way of the idea of critical natural capital [START_REF] Chiesura | Critical Natural Capital : a socio-cultural perspective[END_REF], to the idea of ecosystem service [START_REF] Norgaard | Ecosystem Services: from eye-opening metaphor to complexity blinder[END_REF]. Throughout his career, Norgaard has developed a number of reflections on the metaphorical use of concepts in the environmental field, whether about carrying capacity [START_REF] Norgaard | Metaphors we might survive by[END_REF], ecosystem services [START_REF] Norgaard | Ecosystem Services: from eye-opening metaphor to complexity blinder[END_REF] or, of course, coevolution. In all the cases listed above, the metaphor appears as a powerful medium for awareness of the issues affecting the relationship between environment and development, influenced by a worldview (or a model5 ) and generally leading to directives which are sometimes implicit. For example, Norgaard made a comment in 1995, in a short article published in the journal Ecological Economics, the article published in the journal Science the same year by a group of authors -economists and ecologists -on economic growth, the carrying capacity of ecosystems and the environment [START_REF] Arrow | Economic growth, carryingcapacity, and the environment[END_REF]. The metaphor of carrying capacity, which is common usage in the field of environmental economics and ecological economics (the concept is even the basis of many works in bioeconomy) captures the attention of Norgaard. According to him, even if the conclusions reached by the authors of the article in Science are important (neither economic growth, nor the development of free trade internationally, is the antidote to the environmental crisis), they are still based on the design of mechanistic systems where the idea of limits is meaningful. Conversely, in a coevolutionary context, the idea of limits becomes meaningless. It is in this context that the interdisciplinary dialogue between economists and ecologists must find its foundations, as Norgaard argued at length in his book, Development Betrayed, published a year earlier. Norgaard thus writes (1995:130): "The Science article is strong in that it conveys valuable ideas about biological diversity, ecosystem resilience, the possibilities of multiple environmental system equilibria, and the merits of adaptive environmental management. Nevertheless, the article is still couched in the language and hence processes of mechanical systems rather than, for example, coevolutionary systems. From a co-evolutionary perspective, there are no limits. Everything we do affects how things select on each other and thereby our co-evolution with numerous other species. The metaphor of limits says that if we "control" ourselves more and nature less, living within nature's bounds, we will have a greater chance of survival". The vision of the world that Norgaard defends, one based on coevolution, does not mean that companies should participate in intensive exploitation of natural resources without responding. Thus, the idea of coevolutionary development takes a more political and normative turn, and it is worth taking time to understand the relationship between science and policy in the point of view put forth by Norgaard. However, as stressed by Kallis and Norgaard (2010: 697), "coevolutionary studies are often vague on their policy premises, although they often yield concrete policy conclusions".

The coevolutionary perspective can be a diagnostic tool to trace the historical evolution of the relationship between nature and societies -especially since the Industrial Revolution -and explicitly denouncing a world where the development of Western science and its influence on the relationship that societies have with nature would have led to a vision of Western development in which man remains the master and owner of nature. For example, the development of the use of pesticides in agriculture is a response to human needs, often without concern for the environmental and health impact that is created. Yet, as Norgaard regularly illustrated in his work, with a coevolutionary perspective, the struggle against insects and pests through the use of pesticides causes genetic mutations and adaptations to pesticides by insects and plants, which is the result of a complex set of interactions between the different dimensions of coevolution presented above. But the coevolution between social and environmental systems can also be mobilized as a normative framework, since we associate it with the idea of development. Norgaard (1984:529) thus recognises " [t]he terms to coevolve, coevolution and coevolutionary are value free in this paper and merely refer to the reciprocal process of change. The term coevolutionary development is used to refer to coevolution that benefits man". It is in this sense that [START_REF] Norgaard | Sustainable Development: A Coevolutionary View[END_REF] reinterprets the concept of sustainable development, from a coevolutionary perspective.

Robert Costanza and the concept of "ecosystem service"

Robert Costanza was born in 1950. After studying architecture and regional and urban planning, in 1974 Costanza began a Ph.D. program in Systems Ecology and Environmental Engineering -with a minor in Economics -at the University of Gainesville in Florida, under the direction of Howard Odum. He completed his dissertation in 1979. He then went on to do a postdoctorate at Louisiana State University in 1980-1981. The following year, he was appointed assistant professor in the department of marine sciences. In 1984, production factor, on which the other production factors usually considered by economic theory depend 8 . Hence the idea of using energy indicators to reflect this interdependence. The aim of this article does not stop there. Indeed, his last paragraphs take a decidedly programmatic turn. Invoking the names of economists Boulding, Georgescu-Roegen, and Daly 9 , Costanza then sketches a redefinition of the economy, noting that "the implications for a new ecological economics that links the natural and social sciences are great" [emphasis added]. Although the idea of limits of the biosphere may be clearly indicated -that is the meaning of the reference to Boulding's "cowboy economy" [1966], heralding what would soon be called "strong sustainability" -, this approach does not seek to challenge the approach of the standard economist, but rather to supplement it by giving it a biophysical foundation 10 . Starting with the idea that "[t]he flow of energy is the primary concern of economics", [START_REF] Costanza | Embodied energy and economic valuation[END_REF]Costanza [ :1224] ] calls for us to expand the boundaries of productive systems usually studied by economists; energy values allow us, according to him, to achieve an "internalization of externalities", particularly when there are no other indicators of value and no price signals. In this, Costanza only subscribes to the perspective developed by the Odum brothers, who defined ecology as a "broad economy" [Odum, 1976], including the cost of the works of nature and men.

In the 1980s, Costanza explores the prospect of a merger of monetary assessment and energy assessment, while continuing work in the field of energy efficiency [START_REF] Cleveland | Energy and the US Economy : A biophysical perspective[END_REF]. Thus, during the Wallenberg Symposium on the integration of economy and ecology, held in Stockholm in September 1982 -which is considered one of the first community structuring moments of Ecological Economics [Ropke, 2004: 308] -, Costanza [1984:9] presented a paper in which he stated that, according to him, the main issue in environmental management is finding a way to assign "shadow pricing" to natural resources. From his point of view, Ecological Economics -the term now appears in the title of his article -can offer a lot in this area by relating 8 Costanza [1980:1219-1220] wrote : "[…] practically everything on the earth can be considered to be a direct or indirect product of past and present solar energy […] Fossil fuels and other natural resources represent millions of years of embodied sunlight. Environmental flows (such as winds, rain, and rivers) represent embodied sunlight of more recent origin. Humans, under this view, are the product of millions of years of solar-powered R&D and are maintained by an agriculture that uses both current sunlight and fossil sunlight. From this perspective, industrial capital is obviously created by the economic process and is not a net (or primary) input." 9 Note that he is thanked at the end of the article for his help and comments.

10 "From the ecological perspective, markets can be viewed as an efficient energy allocation device that humans have developed to solve the common problem facing all speciessurvival" [START_REF] Costanza | Embodied energy and economic valuation[END_REF][Costanza, : 1224]].

the economy that studies how resources are allocated within human societies to ecology, which studies how resources are allocated within nature. The task is to relate the two main ways of calculating shadow pricing: that of economists (monetary assessments, particularly through measures of willingness to pay) and that of ecologists (energy analysis). The first approach is based on the information that people have, which is far from perfectdespite efforts by environmental movements promoting awareness of the importance of the environment, which Costanza acknowledges 11 . Furthermore, contrary to the assumption generally followed by standard economists who see them as exogenous, individual preferences are likely to be handled by internal elements in the economic system (Costanza recalls the role of advertising, in particular). Therefore, pleads Costanza, the energy approach can help these individuals -and, more broadly, all decision-makersto understand the importance of the environment for their well-being through the description and evaluation of a set of production relationships. Among the various avenues explored in modelling relationships between biophysical systems and economics, Costanza highlights his energy approach, because it is perfectly congruent with that of standard economists. In fact, according to Costanza (1984:12), if "the markets were perfect", if economic agents were perfectly informed, both types of evaluation, monetary and energy, would be equivalent. In that case, monetary sub-constraint maximization and subconstraint maximization of the energy incorporated into goods would be identical. However, as a precaution, given the limitations faced by different valuation methods -not the least being data availability - Costanza [1984:17] recommends, at the end of his paper, using energy and monetary approaches together.

3.2.The goal of ecological economics: measuring the value of ecosystem services?

To support his claim empirically, Costanza [1984:12] uses in his argument a collaborative work with Christopher Neill from a few years earlier [START_REF] Costanza | The energy embodied int eh products of the biosphere[END_REF] which led to the construction, on the level of the biosphere, of a matrix describing the necessary material and energy flows (9 processes) to produce a certain number of goods and services (9 commodities) to people and nature. This descriptive table of functional relationships between quantities of 11 "The willingness-to-pay approach to shadow pricing environmental resources is therefore effective to the extent of different levels of these resources on their own welfare. The approach of the environmental movement over the last decade has been to try to educate the population about the workings of the environment. To the extent that this has been effective, shadow pricing environmental resources via the willingness-to-pay approach can be successful" [Costanza, 1984:10].

production factors used (solar and fossil energy) and quantities of goods and services produced for people and nature allows us to calculate a set of conversion keys between the amount of embodied energy and the monetary value of the outputs. The inspiration of economic methods in this reasoning and the construction of this general accounting is obvious: it appears close to the matrix of inter-industry trade developed by Leontieff in the 1940s to describe the United States' economy, which, as we know, then was taken as part of the national accounting. We also note in the text a reference to the Production of goods from goods from Sraffa -the difference here being that some production factors and some goods and services are not commodities, but fall within nature's economy. By clearly showing the dependence of the well-being of humanity on the biosphere, this matrix, wrote Costanza [1984:17], is a first step towards the establishment of an ecological economy.

It allows, as suggested by Costanza and Neill [1981:751], policymakers to legitimately raise the question of the value of these goods and "ecosystem services" 12 .

Over time, by continuing on this path of developing environmental accounting, Costanza would use this notion of "ecosystem service" more frankly to designate this economy of nature that he is committed to understanding. This is clear in "Valuation and management of wetland ecosystems", an article published by [START_REF] Costanza | Valuation and management of wetland ecosystems[END_REF] in an early issue of Ecological Economics 13 . In accordance with Costanza's recommendation [1984] to use a variety of assessment methods, these authors compare the energy efficient approach and the monetary approach of a wetland located in Louisiana 14 . They obtain a range of values (from 2,500 to 12 According to Costanza and Neill [1981:751] "The potential utility to environmental managers and decision makers of defendable answers to questions like: what is the true extra-market value of rainfall? Or ecosystem services? Or nonrenewable resources?is enormous".

13 "Unfortunately, for the many ecosystem goods and services that humans do care about […]", write Costanza et al. [1989:336]. 14 As regards the economic assessment, three benefits provided by the zone are identified: commercial fishing and professional hunting; the recreational value of the area; protection against storms. The methods used are taken from the survey of market prices of products sold commercially, the method of transport costs, and the contingent valuation. The energy assessment of the area is based on gross primary productivity of the ecosystem. The authors then estimate what it would cost the company to produce these quantities of energy (by converting fossil energy, which is estimated based on market price). Per acre, in 1983 dollars, with a discount rate of 3%, the monetary assessment is nearly 9,000 dollars, and the energy assessment is from 17,000 to 28,000 dollars. With a discount rate of 8%, the respective figures are 2,400 dollars and 6,400 to 10,000 dollars. 17,000 dollars/acre), which vary depending on the discount rate used; the authors emphasize that the most important changes in their assessments come from this variable... The energy assessment is at the high end of the evaluation, which meant to the authors that the contribution of the environment to the production and well-being of individuals was undervalued by traditional economic approaches. Costanza and his colleagues acknowledge that many uncertainties and flaws remain in their calculations, but their point of view is that it is preferable to have a bad assessment than no assessment at all... This is the same pragmatic view that is defended in the famous article published by [START_REF] Costanza | The value of the world's ecosystem services and natural capital[END_REF] in Nature on the assessment of ecosystem services on the planet. At the same time, we observe a shift: the methods chosen this time are those of standard environmental economics: they relate primarily to the assessment of the willingness of individuals to pay -but there is also reference to land prices, for coastal ecosystems... Still, energy assessments have not completely disappeared from the exercise -a Costanza article et al. [1989] is cited in the bibliography. After having clarified that they were used to making comparisons with the results obtained through monetary assessments, Costanza et al. (1997: 258) conclude: "Interestingly, different methods showed fairly close agreement in the final results".

Although Costanza has not given up the idea of complementarity between monetary and energy approaches -this is evident in the methodological discussion led by him and his colleagues in the introductory article to a special issue of Ecological Economics devoted to the value of ecosystem services [START_REF] Farber | Economic and ecological concepts for valuing ecosystem services[END_REF], which refer to Ricardo and Sraffa15 -, the Nature article is symptomatic of a two-fold evolution that has been observed, especially in the columns in the journal Ecological Economics: first, an increasingly strong focus is placed on ecosystem services -in the name of profound knowledge of natural capital -and, second, an increasingly pronounced appeal for a monetary evaluation of it.

Conclusion

Twenty-five years after the formal establishment of the ISEE, the field of ecological economics has become huge. The books and articles that deal with this framework now number in the tens of thousands. Covering such a field requires the use of specific bibliometric methods. Without denying the interest of these approaches, one must be aware of their limitations: what is gained through the amount of material they can process is sometimes lost because of the lack of precision analysing the content of these writings. We therefore advocate complementary approaches that are established in the field of history of thought, such as, for example, conceptual history and history of research paths. In this first work, which is still largely exploratory, we sought to examine the intersection of these two approaches by studying how the research path of two eminent personalities in the field of Ecological Economics -Richard Norgaard and Robert Costanza -became involved in two innovative concepts of Ecological Economics -the concepts of coevolution and ecosystem service.

A first reading is, as we have pointed out in the introduction, to note the existing symmetry between the first researcher, an economist who was inspired by a concept embraced by ecologists, and the second, an ecologist who has always displayed a strong will to adopt the reasoning of economists. This perfectly illustrates the general philosophy of the Ecological Economics project, which, from the beginning, has aimed to merge these two major scientific communities in order to create new knowledge, particularly through evolving concepts. A second reading deals with the analysis of theoretical proposals made by these two authors: on the one hand, a perspective of allocation and optimization which follows the logic of standard economics, an extended economy, embracing natural and human systems, which was built by Costanza from the development of a theory of value, from the description of a set of transactions and the calculation of a set of shadow prices. In this context, the ecosystem is seen as "natural capital", providing goods and services on which the well-being of human societies depends. The methodological pluralism (sometimes using a calculation method, sometimes another) is then used to provide a unified vision of the relationship between people and the biosphere on a broader basis. On the other hand, from two nonunified scientific fields, ecological economics appears rather as a field of questions. This is another vision of the ecosystem that we encounter (which is also found in Costanza in writings other than the ones we have seen here) as an evolutionary, complex system in constant interaction with social systemswhich leads us to reconsider the very idea of development. Questioning the established metrics and adopted conventions, the methodological pluralism defended by Norgaard, which brings us to the threshold of institutionalist thought, conflicts with that of Costanza. A third reading brings us to the thorny question of limits, which one can consider fundamental in the organization of the area separating ecological economics from the standard economic approach: while they are clearly indicated by Costanza -natural capital is not entirely substitutable -, they become increasingly blurred in Norgaard.

  Richard B. Norgaard, currently Professor Emeritus in Resource and Energy Economics at the University of California, Berkeley, is a founding member of the International Society for Ecological Economicsa Society he also chaired from 1998 to 2001. A trained economist (B.A. in Economics from the University of California, Berkeley, an M.S. in Agricultural Economics from Oregon State University, and a Ph.D. in economics from the University of Chicago

For the moment, we would like to use the generic term for the subject. We shall see later that these subjects may be alternatively (and often also simultaneously) used as metaphors, concepts, and instruments of public policy.

For the moment, we would like to use the generic term for the subject. We shall see later that these subjects may be alternatively (and often also simultaneously) used as metaphors, concepts, and instruments of public policy.

Norgaard nevertheless cites Paul Ehrlich in the acknowledgments of his 1981 article, and Ehrlich figures, through another reference, in the final bibliography of this article.

It brings to mind as much the invisible hand of Adam Smith as the economic circuit developed by François Quesnay, likening it to the circulation of blood in the human body.

According toBaumgärtner et al. (2008:389), "A model is an abstract representation of a system under study, explicitly constructed for a certain purpose, and based on the concepts within a scientific community's basic construction of the world that are considered relevant for the purpose".

"Available energy is thus the only 'basic' commodity and is ultimately the only 'scarce' factor of production, thereby satisfying the criteria for a production-based theory that can explain exchange values"[Farber et al., 2002: 382].

he became a professor in the biology department of the University of Maryland. In the wake of Howard T. Odum, Costanza would play a leading role in the structuring and activity planning of the Ecological Economics community -it is probably to him that we owe this term. He is one of the cofounders of the International Society for Ecological Economics (ISEE), and he was editor-in-chief of the journal Ecological Economics from 1989 to 2002. In 2002, he was appointed Professor of Ecological Economics at the University of Vermont. Since 2013, he has been a professor at the Crawford School of Public Policy at the Australian National University in Canberra.

Before looking at how the concept of "ecosystem service" emerged and was mobilized centrally by Costanza to characterize the process of ecological economics, we will return to his conception of ecology as an economy of nature.

3.1.From the economy of nature to ecological economics

After defending his dissertation in 1979, Costanza was invited the next year by H. Daly to present his work at a symposium entitled "Energy, Economics, and the Environment". [START_REF] Costanza | Embodied energy and economic valuation[END_REF] takes up the idea expressed, among others, by H.T. [START_REF] Odum | Environment, Power and Society[END_REF] in the 1970s 6 , a theory of energy value based on the amount of energy embedded in complex systems (the energy can be considered "as the monetary standard of ecology," wrote E.P. Odum [1971:39]). He also shows, from a case study of the U.S. economy, that there is a strong correlation between the energy embodied in goods and services produced by different sectors of that economy and their monetary value expressed as gross national product. This is, as Costanza 7 emphasizes, a "theory of value production cost", which explains the values of exchange. This approach captures what usually escapes the monetary measure of production, namely the energy used indirectly to produce goods (solar energy incorporated into agricultural products, for example) and work. It also allows us to calculate the value when there is no market or price -which is the case with most relationships with the environment. The backdrop of this research is the idea that energy -and, more broadly, nature -is a kind of "primary" 6 Costanza [1980] also refers to the work of L. von Boltzmann, F. Soddy, F. Cottrell, and B. Hannon. As I. Ropke [2004: 307] reminds us, Costanza met with the latter at the University of Illinois during his doctoral research to do the work of energy modelling of ecological and economic systems. 7 Costanza [1980: 1224] wrote : "An embodied energy theory of value thus makes sense and is empirically accurate only if the system boundaries are defined in an appropriate way. It is really a cost-of-production theory with all costs carried back to the solar energy necessary directly and indirectly to produce them".