Online research in philosophy

This paper reviews the psychological investigation of reasoning with conditionals, putting an emphasis on recent work. In the first part, a few methodological remarks are presented. In the second part, the main theories of deductive reasoning (mental rules, mental models, and the probabilistic approach) are considered in turn; their content is summarised and the semantics they assume for if and the way they explain formal conditional reasoning are discussed, in particular in the light of experimental work on the probability of conditionals. The last part presents the recent shift of interest towards the study of conditional reasoning in context, that is, with large knowledge bases and uncertain premises.

Espino, Santamaria, and Garcia-Madruga (2000) report three results on the time taken to respond to a probe word occurring as end term in the premises of a syllogistic argument. They argue that these results can only be predicted by the theory of mental models. It is argued that two of these results, on differential reaction times to end-terms occurring in different premises and in different figures, are consistent with Chater and Oaksford's (1999) probability heuristics model (PHM). It is argued that the third finding, on different reaction times between figures, does not address the issue of processing difficulty where PHM predicts no differences between figures. It is concluded that Espino et al.'s results do not discriminate between theories of syllogistic reasoning as effectively as they propose.

An experimental study is reported which investigates the differences in interpretation between content conditionals (of various pragmatic types) and inferential conditionals. In a content conditional, the antecedent represents a requirement for the consequent to become true. In an inferential conditional, the antecedent functions as a premise and the consequent as the inferred conclusion from that premise. The linguistic difference between content and inferential conditionals is often neglected in reasoning experiments. This turns out to be unjustified, since we adduced evidence on the basis of a quantitative and a qualitative analysis that this difference has a manifest psychological relevance. For the inferential conditionals, participants appear to retrieve the order of events of the original content conditional on which it was based, before they start reasoning with it. The implications of this finding for reasoning research and linguistics will be discussed.

Four experiments investigated uncertainty about a premise in a deductive argument as a function of the expertise of the speaker and of the conversational context. The procedure mimicked everyday reasoning in that participants were not told that the premises were to be treated as certain. The results showed that the perceived likelihood of a conclusion was greater when the major or the minor premise was uttered by an expert rather than a novice (Experiment 1). The results also showed that uncertainty about the conclusion was higher when the major premise was uttered by a novice and an alternative premise by an expert, compared to when the major premise was uttered by an expert and the alternative by a novice (Experiment 2). Similarly, the believability of a conclusion was considerably lower when the minor premise was uttered by a novice and denied by an expert, as opposed to when an expert uttered the minor premise and a novice denied it (Experiment 3). Experiment 4 showed that the nature of the uncertainty induced by a denial of the minor premise depended on whether or not the context was a conversation. These results pose difficult problems for current theories of reasoning, as current theories are based on the results of experiments in which the premises are treated as certain. Our discussion of the results emphasises the importance of pragmatics in reasoning, namely, the role of general knowledge about the world in assessing the probability of a premise uttered by an expert or a novice and the role of interpretations of the premise based on pragmatic inferences in revising these initial probabilities.

According to the mental models theory, reasoning performance is primarily influenced by the number of models of a problem that can be constructed. This study investigates whether the content of the model may also influence performance. Linear reasoning problems were devised that either described a believable (script-consistent) or an unbelievable (script-inconsistent) order of actions. The results of two experiments showed that conclusions were inferred more slowly and less accurately on the basis of an unbelievable model than on a believable one. Experiment 2 revealed that script knowledge facilitated as well as impeded reasoning performance. Conclusion evaluation was faster and more accurately for script-consistent problems than for neutral problems, whereas model construction and conclusion evaluation occurred respectively more slowly and less accurately for script-inconsistent problems than for neutral problems. These results show that the content of the model is a noteworthy factor influencing reasoning performance.

Four experiments investigated the effects of probability manipulations on the indicative four card selection task (Wason, 1966, 1968). All looked at the effects of high and low probability antecedents (p) and consequents (q) on participants' data selections when determining the truth or falsity of a conditional rule, if p then q . Experiments 1 and 2 also manipulated believability. In Experiment 1, 128 participants performed the task using rules with varied contents pretested for probability of occurrence. Probabilistic effects were observed which were partly consistent with some probabilistic accounts but not with non-probabilistic approaches to selection task performance. No effects of believability were observed, a finding replicated in Experiment 2 which used 80 participants with standardised and familiar contents. Some effects in this experiment appeared inconsistent with existing probabilistic approaches. To avoid possible effects of content, Experiments 3 (48 participants) and 4 (20 participants) used abstract material. Both experiments revealed probabilistic effects. In the Discussion we examine the compatibility of these results with the various models of selection task performance.

This study investigated individual differences in the belief bias effect, which is the tendency to accept conclusions because they are believable rather than because they are logically valid. It was observed that the extent of an individual's belief bias effect was unrelated to a number of measures of reasoning competence. Instead, as predicted by mental models theory, it was related to a person's ability to generate alternative representations of premises: the more alternatives a person generated, the less likely they were to show a belief bias effect. In contrast to belief effects, which were predicted by the number of alternatives generated, scores on logical reasoning tasks were predicted by an individual's understanding of the concept of logical necessity. These two mediating variables, ability to generate alternatives and understanding of logical necessity, were themselves predicted by similar variables, such as cognitive motivation and abstract reasoning ability. Our findings strongly support the mental models interpretation of the belief bias effect, and suggest that individual differences in this effect are associated with a specific ability to generate alternatives, rather than with a general logical competence.

Two experiments investigated the factors that people consider when evaluating informal arguments in newspaper and magazine editorials. Experiment 1 showed that subjects were more likely to object to the truth of the premises and the conclusions of an argument than to the strength of the link between them. Experiment 1 also revealed two manipulations that helped subjects object to the link between premises and conclusions: rating how well the premises support the conclusions and rating the believability of the premises and conclusions. Experiment 2 further demonstrated that subjects who identified the premises and conclusions of an argument were better at formulating objections to the link between premises and conclusions. Moreover, subjects in Experiment 2 were better and faster at formulating objections to the truth of the premises and conclusions than to the link between premises and conclusions. The results are discussed in terms of the constraints they pose for developing a cognitive theory of informal reasoning.

We report the results of three experiments designed to assess the role of suppositions in human reasoning. Theories of reasoning based on formal rules propose that the ability to make suppositions is central to deductive reasoning. Our first experiment compared two types of problem that could be solved by a suppositional strategy. Our results showed no difference in difficulty between problems requiring affirmative or negative suppositions and very low logical solution rates throughout. Further analysis of the error data showed a pattern of responses, which suggested that participants reason from a superficial representation of the premises in these arguments and this drives their choice of conclusion. Our second experiment employed a different set of suppositional problems but with extremely similar proofs in terms of the rules applied and number of inferential steps required. As predicted by our interpretation of reasoning strategies employed in Experiment 1, logical performance was very much higher on these problems. Our third experiment showed that problems that could be solved by constructing an initial representation of the premises were easier than problems in which this representation was not sufficient. This effect was independent of the suppositional structure of the problems. We discuss the implications of this research for theories of reasoning based on mental models and inference rules.

Some studies have reported that, under some circumstances, participants sometimes reject the truth of conditional premises and give incorrect uncertain conclusions to MP and MT, despite the standard instructions to assume the truth of the premises. Instructions that emphasise the logical nature of the task, on the other hand, increase the number of valid conclusions to these two inferences. In this paper, we examine two possible explanations for the influence of instructions on the production of valid conclusions: (1) instructions trigger a logical mode of thinking that is appropriate for the task to be solved, and (2) instructions affect the way that retrieved information is used when constructing a mental representation of the premises. In order to compare these two hypothesis, we used conditional causal relations having either many or few disabling conditions (i.e. cases of P and not-Q) and presented them in four different instructional conditions. When presented with the standard instructions to suppose the premises to be true, MP and MT inferences show a relatively low percentage of valid conclusions. However, when the logical nature of the task and the necessity to assume the truth of the premises are emphasised, the number of valid conclusions greatly increases. Also, if disabling conditions are made explicit or generated before the presentation of these logical instructions, the performance on MP and MT is lower than when only the logical instructions are presented. Finally, the instructions had no effect on AC and DA. From these results, we concluded that the instructions had an effect on the use of retrieved information rather than on inducing different modes of thinking.