Cedric Paternotte

Robustness analysis is widespread in science, but philosophers have struggled to justify its confirmatory power. We provide a positive account of robustness by analysing some explicit and implicit uses of within and across-model robustness in evolutionary theory. We argue that appeals to robustness are usually difficult to justify because they aim to increase the likeliness that a phenomenon obtains. However, we show that robust results are necessary for explanations of phenomena with specific properties. Across-model robustness is necessary for how-possibly explanations of multiply instantiated phenomena, while within-model robustness is necessary for explanations of phenomena with multiple evolutionary starting points. In such cases, the appeal of robustness is explanatory rather than confirmatory.

We critically examine a number of aspects of Grafen’s ‘formal Darwinism’ project. We argue that Grafen’s ‘selection-optimality’ links do not quite succeed in vindicating the working assumption made by behavioural ecologists and others—that selection will lead organisms to exhibit adaptive behaviour—since these links hold true even in the presence of strong genetic and developmental constraints. However we suggest that the selection-optimality links can profitably be viewed as constituting an axiomatic theory of fitness. Finally, we compare Grafen’s project with Fisher’s ‘fundamental theorem of natural selection’, and we speculate about whether Grafen’s results can be extended to a game-theoretic setting

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.

Recent years have witnessed an increased number of game-theoretic approaches to social norms, which apparently share some common vocabulary and methods. We describe three major approaches of this kind (due to Binmore, Bicchieri and Gintis), before comparing them systematically on five crucial themes: generality of the solution, preference transformation, punishment, epistemic conditions and type of explanation. This allows us to show that these theories are, by and large, less compatible than they seem. We then argue that those three theories struggle to account for three phenomena pertaining to social norms (namely context-dependence, conflicting norms and self-evidence), with which any complete game-theoretic account should in principle be able to deal.

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.

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.

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.