The fact that much of our knowledge is gained through the testimony of others challenges a certain form of epistemic individualism. We are clearly not autonomous knowers. But the discussion surrounding testimony has maintained a commitment to what I have elsewhere called epistemic agent individualism. Both the reductionist and the anti-reductionist have focused their attention on the testimony of individuals. But groups, too, are sources of testimony - or so I shall argue. If groups can be testifiers, a natural question (...) to ask is whether our beliefs based on the testimony of groups are ever justified and whether such a justification is to be conferred inferentially or non-inferentially. I consider and dismiss the possibility of extending an anti-reductionist account of justification to our group testimonial beliefs. I also argue against a version of reductionism that would have our group testimonial beliefs justified only in so far as we were able to monitor the trustworthiness of members of the group. However, there are forms of reductionism that can be extended to make sense of the justification of our group testimonial beliefs. There are mechanisms for monitoring the trustworthiness and competency of a group (rather than its members) and, further, a variety of background beliefs allow us to assess the testimony of a group for reliability. (shrink)

Public discussions of political and social issues are often characterized by deep and persistent polarization. In social psychology, it’s standard to treat belief polarization as the product of epistemic irrationality. In contrast, we argue that the persistent disagreement that grounds political and social polarization can be produced by epistemically rational agents, when those agents have limited cognitive resources. Using an agent-based model of group deliberation, we show that groups of deliberating agents using coherence-based strategies for managing their limited resources tend (...) to polarize into different subgroups. We argue that using that strategy is epistemically rational for limited agents. So even though group polarization looks like it must be the product of human irrationality, polarization can be the result of fully rational deliberation with natural human limitations. (shrink)

In this paper we present the results of a simulation study of credence developments in groups of communicating Bayesian agents, as they update their beliefs about a given proposition p. Based on the empirical literature, one would assume that these groups of rational agents would converge on a view over time, or at least that they would not polarize. This paper presents and discusses surprising evidence that this is not true. Our simulation study shows that these groups of Bayesian agents (...) show group polarization behavior under a broad range of circumstances. This is, we think, an unexpected result, that raises deeper questions about whether the kind of polarization in question is irrational. If one accepts Bayesian agency as the hallmark of epistemic rationality, then one should infer that the polarization we find is also rational. On the other hand, if we are inclined to think that there is something epistemically irrational about group polarization, then something must be off in the model employed in our simulation study. We discuss several possible interfering factors, including how epistemic trust is defined in the model. Ultimately, we propose that the notion of Bayesian agency is missing something in general, namely the ability to respond to higher-order evidence. (shrink)

In this paper, I provide the framework for an account of group assertion. On my view, there are two kinds of group assertion, coordinated and authority-based, with authority-based group assertion being the core notion. I argue against a deflationary view, according to which a group’s asserting is understood in terms of individual assertions, by showing that a group can assert a proposition even when no individual does. Instead, I argue on behalf of an inflationary view, according to which it is (...) the group itself that asserts, a conclusion supported by the fact that paradigmatic features of assertion apply only at the level of the group. A central virtue of my account is that it appreciates the important relationship that exists between most groups and their spokespersons, as well as the consequences that follow from this relationship. My view, thus, provides the framework for distinguishing when responsibility for an assertion lies at the collective level, and when it should be shouldered by an individual simply speaking for herself. (shrink)

We gain information from collective, often institutional bodies all the time—from the publications of committees, news teams, or research groups, from web sites such as Wikipedia, and so on—but do these bodies ever function as genuine group testifiers as opposed to mere group sources of information? In putting the question this way I invoke a distinction made, if briefly, by Edward Craig, which I believe to be of deep significance in thinking about the distinctiveness of the speech act of testimony. (...) The distinction is that between somebody’s functioning as a ‘good informant’ and their functioning merely as a ‘source of information’. The difference between these has, as he remarks, a crucial ethical aspect: What I have in mind is the special flavour of situations in which human beings treat each other as subjects with a common purpose, rather than as objects from which services, in this case true belief, can be extracted. In this paper I shall try to bring out the distinctive nature of the role of good informant in a way that helps to clarify what is at stake in asking whether there can be group testimony in the sense of genuinely collective testimony—that is to say, where the group testifier is a collective and not merely a sum of individuals testifying in one or another form of aggregated chorus. (shrink)

Polarization is a topic of intense interest among social scientists, but there is significant disagreement regarding the character of the phenomenon and little understanding of underlying mechanics. A first problem, we argue, is that polarization appears in the literature as not one concept but many. In the first part of the article, we distinguish nine phenomena that may be considered polarization, with suggestions of appropriate measures for each. In the second part of the article, we apply this analysis to evaluate (...) the types of polarization generated by the three major families of computational models proposing specific mechanisms of opinion polarization. (shrink)

The principle of homophily says that people associate with other groups of people who are mostly like themselves. Many online communities are structured around groups of socially similar individuals. On Twitter, however, people are exposed to multiple, diverse points of view through the public timeline. The authors captured 30,000 tweets about the shooting of George Tiller, a late-term abortion doctor, and the subsequent conversations among pro-life and pro-choice advocates. They found that replies between like-minded individuals strengthen group identity, whereas replies (...) between different-minded individuals reinforce in-group and out-group affiliation. Their results show that people are exposed to broader viewpoints than they were before but are limited in their ability to engage in meaningful discussion. They conclude with implications for different kinds of social participation on Twitter more generally. (shrink)

Are companies, churches, and states genuine agents? Or are they just collections of individuals that give a misleading impression of unity? This question is important, since the answer dictates how we should explain the behaviour of these entities and whether we should treat them as responsible and accountable on the model of individual agents. Group Agency offers a new approach to that question and is relevant, therefore, to a range of fields from philosophy to law, politics, and the social sciences. (...) Christian List and Philip Pettit argue that there really are group or corporate agents, over and above the individual agents who compose them, and that a proper approach to the social sciences, law, morality, and politics must take account of this fact. Unlike some earlier defences of group agency, their account is entirely unmysterious in character and, despite not being technically difficult, is grounded in cutting-edge work in social choice theory, economics, and philosophy. (shrink)