Cedric Paternotte

We consider the question: under what circumstances can the concept of adaptation be applied to groups, rather than individuals? Gardner and Grafen (2009, J. Evol. Biol.22: 659–671) develop a novel approach to this question, building on Grafen's ‘formal Darwinism’ project, which defines adaptation in terms of links between evolutionary dynamics and optimization. They conclude that only clonal groups, and to a lesser extent groups in which reproductive competition is repressed, can be considered as adaptive units. We re-examine the conditions under which the selection–optimization links hold at the group level. We focus on an important distinction between two ways of understanding the links, which have different implications regarding group adaptationism. We show how the formal Darwinism approach can be reconciled with G.C. Williams’ famous analysis of group adaptation, and we consider the relationships between group adaptation, the Price equation approach to multi-level selection, and the alternative approach based on contextual analysis.

Ordinary common knowledge is formally expressed by strong probabilistic common belief. How strong exactly? The question can be answered by drawing from the similar equivalence, recently explored, between plain and probabilistic individual beliefs. I argue that such a move entails that common knowledge displays a double fragility: as a description of a collective state and as a phenomenon, because it can respectively disappear as group size increases, or more worryingly as the epistemic context changes. I argue that despite this latter fragility, the effects of common knowledge on action are robust. Unfortunately, this in turn leads to a third fragility, that of the concept of common knowledge, which threatens to collapse on probabilistic common belief. This also reveals a disanalogy between the individual and the collective cases. I finally pinpoint the subtle difference entailed by the two concepts, expressed in terms of the attitude towards contrary evidence or of the agents’ awareness. As a result, common knowledge can be defended as a concept, which refers to a fragile yet distinct collective attitude.

Over the last three decades, joint action has received various definitions, which for all their differences share many features. However, they cannot fit some perplexing cases of weak joint action, such as demonstrations, where agents rely on distinct epistemic sources, and as a result, have no first-hand knowledge about each other. I argue that one major reason why the definition of such collective actions is akin to the classical ones is that it crucially relies on the concept of common knowledge. To this end, I first argue for the necessity of common knowledge for joint action in general due to the increased reliability of success it entails. I then defend the relevance of common knowledge against several criticisms, point at an adequate weakening, and discuss alternative approaches. Although structurally weaker, the common knowledge has a richer content in weak joint actions. As a result, even if the links between individuals are seriously stretched, much is still shared among them. Weak joint actions still require considerable cognitive abilities indeed

There exist many definitions of human joint action, or of what makes a group similar to an individual. However, they do not agree and are not directly reducible to each other. This multiplicity is due to a lack of constraints on them. I argue that they should at least meet an efficiency constraint: any account of joint action has to justify how it reliably leads agents to cooperation. One avenue consists in exploring the analogy between definitions of joint action and of biological individuality. The main components for biological individuality have been identified and their relations are much better understood than those between the components of human joint action. I show that there are surprisingly strong analogies between the criteria and mechanisms for joint action and for biological individuality. As a result, we can import some insights of the biological literature to define what a joint action is, and when a group can and should be considered as an individual.

La plupart des nombreuses définitions existantes d’une action coopérative en fournissent des conditions suffisantes plutôt que nécessaires. Nous définissons ici une forme minimale de coopération, correspondant aux actions de masse, telles des manifestations. Nous en détaillons les aspects intentionnel, épistémique, stratégique et téléologique, généralement obtenus par affaiblissement spécifique de concepts classiques. Parallèlement, nous soulignons le rôle crucial de concepts issus de la théorie des jeux pour la définition d’une action coopérative. Enfin, nous soutenons que la rationalité d’une action coopérative minimale est cruciale à sa réalisation et pas seulement possible ou souhaitable comme le soutiennent les analyses habituelles.

There has been a significant interest in the recent literature in developing a solution to the problem of theory choice which is both normative and descriptive, but agent-based rather than rule-based, originating from Pierre Duhem’s notion of ‘good sense’. In this paper we present the properties Duhem attributes to good sense in different contexts, before examining its current reconstructions advanced in the literature and their limitations. We propose an alternative account of good sense, seen as promoting social consensus in science, and show that it is superior to its rivals in two respects: it is more faithful to Duhemian good sense, and it cashes out the effect that virtues have on scientific progress. We then defend the social consensus account against objections that highlight the positive role of diversity and division of labour in science