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Our beliefs and opinions are shaped by others, making our social networks crucial in determining what we believe to be true. Sometimes this is for the good because our peers help us form a more accurate opinion. Sometimes it is for the worse because we are led astray. In this context, we address via agent-based computer simulations the extent to which patterns of connectivity within our social networks affect the likelihood that initially undecided agents in a network converge on a true opinion following group deliberation. The model incorporates a fine-grained and realistic representation of belief (opinion) and trust, and it allows agents to consult outside information sources. We study a wide range of network structures and provide a detailed statistical analysis concerning the exact contribution of various network metrics to collective competence. Our results highlight and explain the collective risks involved in an overly networked or partitioned society. Specifically, we find that 96% of the variation in collective competence across networks can be attributed to differences in amount of connectivity (average degree) and clustering, which are negatively correlated with collective competence. A study of bandwagon or “group think” effects indicates that both connectivity and clustering increase the probability that the network, wholly or partly, locks into a false opinion. Our work is interestingly related to Gerhard Schurz’s work on meta-induction and can be seen as broadly addressing a practical limitation of his approach.

Cytotoxic T lymphocytes patrol our body in search for infected cells which they kill through the release of cytotoxic substances contained in cytotoxic granules. The fusion of cytotoxic granules occurs at a specially formed contact site, the immunological synapse, and is tightly controlled to ensure specificity. In this review, we discuss the contribution of two intracellular compartments, endosomes and cytotoxic granules, to the formation, function and disassembly of the immunological synapse. We highlight a recently proposed sequential process of fusion events at the IS upon target cell recognition. First, recycling endosomes fuse with the plasma membrane to deliver cargo required for the docking of cytotoxic granules. Second, cytotoxic granules arrive and fuse upon docking in a SNARE-dependent manner. Following fusion, membrane components of the cytotoxic granule are retrieved through endocytosis to ensure the fast, efficient serial killing of target cells that is characteristic of cytotoxic T lymphocytes.

Norms—that is, specifications of what we ought to do—play a critical role in the study of informal argumentation, as they do in studies of judgment, decision-making and reasoning more generally. Specifically, they guide a recurring theme: are people rational? Though rules and standards have been central to the study of reasoning, and behavior more generally, there has been little discussion within psychology about why (or indeed if) they should be considered normative despite the considerable philosophical literature that bears on this topic. In the current paper, we ask what makes something a norm, with consideration both of norms in general and a specific example: norms for informal argumentation. We conclude that it is both possible and desirable to invoke norms for rational argument, and that a Bayesian approach provides solid normative principles with which to do so.

Inspired by the principles used to market physical products, campaigns to promote pro-environmental behaviour have increasingly emphasized self-interested (for example, economic) reasons for engaging with a self-transcendent cause (that is, protecting the environment)1, 2. Yet, psychological evidence about values and behaviour suggests that giving self-interested reasons, rather than self-transcending reasons, to carry out a self-transcending action should be ineffective at increasing self-transcending behaviour more generally3, 4. In other words, such a campaign may fail to cause spillover, or an increase in other, different environmental behaviours5. Here we show that recycling rates are dependent on the information participants receive about a separate environmental behaviour, car-sharing (carpooling in the USA). In two experiments, we found that recycling was significantly higher than control when participants received environmental information about car-sharing, but was no different from control when they received financial information or (in experiment 2) received both financial and environmental information. Our results suggest that, congruent with value theory, positive spillover from one environmental message to another behaviour (car-sharing to recycling) may occur primarily when self-transcending reasons alone are made salient.

In a recent article in Argumentation, O’Keefe (Argumentation 21:151–163, 2007) observed that the well-known ‘framing effects’ in the social psychological literature on persuasion are akin to traditional fallacies of argumentation and reasoning and could be exploited for persuasive success in a way that conflicts with principles of responsible advocacy. Positively framed messages (“if you take aspirin, your heart will be more healthy”) differ in persuasive effect from negative frames (“if you do not take aspirin, your heart will be less healthy”), despite containing ‘equivalent’ content. This poses a potential problem, because people might be unduly (and unsuspectingly) influenced by mere presentational differences. By drawing on recent cognitive psychological work on framing effects in choice and decision making paradigms, however, we show that establishing whether two arguments are substantively equivalent—and hence, whether there is any normative requirement for them to be equally persuasive—is a difficult task. Even arguments that are logically equivalent may not be information equivalent. The normative implications of this for both speakers and listeners are discussed.

The notion of “the burden of proof” plays an important role in real-world argumentation contexts, in particular in law. It has also been given a central role in normative accounts of argumentation, and has been used to explain a range of classic argumentation fallacies. We argue that in law the goal is to make practical decisions whereas in critical discussion the goal is frequently simply to increase or decrease degree of belief in a proposition. In the latter case, it is not necessarily important whether that degree of belief exceeds a particular threshold (e.g., ‘reasonable doubt’). We explore the consequences of this distinction for the role that the “burden of proof” has played in argumentation and in theories of fallacy.

We examine in detail three classic reasoning fallacies, that is, supposedly ``incorrect'' forms of argument. These are the so-called argumentam ad ignorantiam, the circular argument or petitio principii, and the slippery slope argument. In each case, the argument type is shown to match structurally arguments which are widely accepted. This suggests that it is not the form of the arguments as such that is problematic but rather something about the content of those examples with which they are typically justified. This leads to a Bayesian reanalysis of these classic argument forms and a reformulation of the conditions under which they do or do not constitute legitimate forms of argumentation.

In this paper, it is argued that Ferguson’s (2003, Argumentation 17, 335–346) recent proposal to reconcile monotonic logic with defeasibility has three counterintuitive consequences. First, the conclusions that can be derived from his new rule of inference are vacuous, a point that as already made against default logics when there are conflicting defaults. Second, his proposal requires a procedural “hack” to the break the symmetry between the disjuncts of the tautological conclusions to which his proposal leads. Third, Ferguson’s proposal amounts to arguing that all everyday inferences are sound by definition. It is concluded that the informal logic response to defeasibility, that an account of the context in which inferences are sound or unsound is required, still stands. It is also observed that another possible response is given by Bayesian probability theory (Oaksford and Chater, in press, Bayesian Rationality: The Probabilistic Approach to Human Reasoning, Oxford University Press, Oxford, UK; Hahn and Oaksford, in press, Synthese).

Case-based Reasoning (CBR) began as a theory of human cognition, but has attracted relatively little direct experimental or theoretical investigation in psychology. However, psychologists have developed a range of instance-based theories of cognition and have extensively studied how similarity to past cases can guide categorization of new cases. This paper considers the relation between CBR and psychological research, focussing on similarity in human and artificial case-based reasoning in law. We argue that CBR, psychology and legal theory have complementary contributions to understanding similarity, and describe what each offers. This allows us to establish criteria for assessing existing CBR systems in law and to establish what we consider to be the crucial goals for further research on similarity, both from a psychological and a CBR perspective.