The power PC theory postulates a normative procedure for making causal inferences from contingency information, and offers this as a descriptive model of human causal judgement. The inferential procedure requires a set of assumptions, which includes the assumption that the cause being judged is distributed independently of the set of other possible causes of the same outcome. It is argued that this assumption either never holds or can never be known to hold. It is also argued that conformity of judgements to the prescriptions of the model requires a sophisticated appreciation of methodological factors and acquired domain-specific knowledge of causes, and that the theory is disconfirmed by a finding that an objective contingency that equally supports two causal inferences results in only one of them actually being made. An alternative proposal based on the hypothesis that causal understanding originates with experiences of forces exerted while acting on objects is briefly sketched.

Two studies are reported which demonstrate that analytic responding on everyday reasoning problems can be increased and bias eliminated after training on the law of large numbers (Fong, Krantz, & Nisbett, 1986). Critical thinking problems involving belief-consistent, neutral, and inconsistent conclusions were presented. Belief bias was eliminated when a written justification of argument strength was elicited. However, belief-based responding was still evident when evaluations of the arguments were elicited using rating scales. This finding demonstrates a dissociation between analytic and belief-based responding as a function of response format. In Experiment 2 an instructional condition designed to foster decontextualised reasoning was included but was ineffective in reducing the degree to which judgements were biased by beliefs. It was concluded that training which makes available the analytic strategies necessary to evaluate a problem has the potential to facilitate performance only if the requested response triggers conscious deliberation of the evidence.

Using a latent variable modelling strategy we study individual differences in patterns of answers to the selection task and to the truth table task. Specifically we investigate the prediction of mental model theory according to which the individual tendency to select the false consequent card (in the selection task) is negatively correlated with the tendency to judge the false antecedent cases as irrelevant (in the truth table task). We fit a psychometric model to two large samples (N = 486, twice), and find no evidence for this negative correlation. We examine which of the assumptions of the model theory must be amended to accommodate our findings.

This paper develops the view that in arguing informally individuals construct a dual representation in which there is a coupling of arguments and the structure of the qualitative (mental) causal model to which these refer. Invited to consider a future possibility, individuals generate a causal model and mentally simulate the consequences of certain actions. Their arguments refer to the causal paths in the model. Correspondingly, faced with specific arguments about a policy option they generate a model with particular causal paths and mentally simulate the outcomes. The results of Experiment 1 are consistent with this notion. Decisions on the percentage of funds to be allocated to genetically modified (GM) crop research depended on the structure of the arguments elicited in response to imagining a future state of affairs. Specifically, the presence of a dissuasive argument eliminated the impact of any persuasive argument. The non-monotonic properties of everyday informal argument can then be seen as a corollary of change to causal structure in the model. The dual representation view predicts that the impact of a dissuasive argument will depend on the structure of the causal model. Experiment 2 tested and confirmed this prediction by requiring individuals to judge the relative persuasiveness of two cases referring either to a model with two independent causal paths or to a model in which one causal path depended on the other. In contrast to Experiment 1, prior opinion on GM crop research did not affect allocation decisions. An advisory role in contrast to a participant role may encourage a more decontextualised mode of thinking. According to the dual representation view, ease of mental simulation should exert wide-ranging effects on judgements and the rhetoric of arguments should also be important. The paper concludes with a discussion of some of these expectations.

The present study tested the existence of a cognitive schema that guides people's evaluations of the likelihood that observed problem-solving processes will succeed. The hypothesised schema consisted of attributes that were found to distinguish between retrospective case reports of successful and unsuccessful real world problem solving (Lipshitz & Bar Ilan, 1996). Participants were asked to evaluate the likelihood of success of identical cases of problem solving that differed in the presence or absence of diagnosis, the selection of appropriate or inappropriate solutions, and the pairing of diagnosis with appropriate or non-appropriate solutions. Consistent with the proposition, diagnosis affected perceived likelihood of success, albeit only when solution quality was held constant, and appropriate diagnosis with a compatible solution produced higher perceived likelihood of success than appropriate diagnosis with incompatible solutions. In addition, results showed that solution quality played a significant role, and that compatibility with a six-phase rational model of problem solving played no role in judging likelihood of success.

From certain sorts of premise, individuals reliably infer invalid conclusions. Two Experiments investigated a possible cause for these illusory inference: Reasoners fail to think about what is false. In Experiment 1, 24 undergraduates drew illusory and control inferences from premises based on exclusive disjunctions (“or else”). In one block, participants were instructed to falsify the premises of each illusory and control inference before making the inference. In the other block, participants did not receive these instructions. There were more correct answers for illusory disjunctions whose premises had been falsified than there were for illusory disjunctions that had not been falsified. A second Experiment introduced illusory inferences in a real world context that accentuated falsification of premises. Accuracy also improved. Knowledge of how to falsify premises and to consider their implications for true premises transferred to a new problem introduced at the end of the Experiment without the falsification instruction. The participants' ratings of the difficulty of the inferences showed that they did not err simply because illusory inferences are perceived to be more difficult than control problems. The model theory predicts these results because it postulates that the limitations of working memory preclude the representation of false information.

The “Asian disease” problem (Tversky & Kahneman, 1981) demonstrated behaviour in contradiction to the invariance axiom of EU theory. However, the risky choice behaviour was simply seen by the equate-to-differentiate model as a choice between the best possible outcomes or a choice between the worst possible outcomes. It was then argued that a way in which frame influences choice is through the perceived difference between possible outcomes. A “judgement” task was designed to examine whether the knowledge of “the value difference between each possible outcome and the certain outcome” will permit prediction of preference in the choice pattern related to the Asian disease problem. Participants were exposed to an anthrax disease problem (the original or probabilistic version of the Asian disease problem) and a SARS problem (the fuzzy version of the Asian disease problem). It was shown that the empirical evidence in relation to the Asian disease problem could be satisfactorily accounted for by the generalised weak dominance strategy revealed by the judgement results.

This study aimed to investigate whether a range of tasks that have been generally classed as requiring insight form an empirically separable group of tasks distinct from tasks generally classed as non-insight. In this study, 24 insight tasks, 10 non-insight tasks, and tests of individual differences in cognitive abilities and working memory were administered to 60 participants. Cluster analysis of the problem-solving tasks indicated that the presumed insight problems did tend to cluster with other presumed insight problems, and similarly the presumed non-insight problems tended to cluster with other presumed non-insight tasks. Performance on presumed insight problems was particularly linked to measures of ideational flexibility with a different pattern of results for the non-insight tasks. Spatial insight problems were linked to spatial flexibility and verbal insight tasks were linked to vocabulary scores. The results are discussed in relation to recent developments of dual process theories of thinking.

Current conceptions of the nature of human reasoning make it no longer tenable to assess children's inference by reference to the norms of logical inference. Alternatively, the complexity of the mental models employed in children's inferences can be analysed. This approach is applied to transitive inference, class inclusion, categorical induction, theory of mind, oddity, categorical syllogisms, analogy, and reasoning deficits. It is argued that a coherent account of children's reasoning emerges in that there is correspondence between tasks at the same level of complexity across different domains, and that the inferences of younger children, while impressive and important, are consistently simpler than those of older children.