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This paper is about syllogistic reasoning, i.e., reasoning from such pairs of premises as, All the chefs are musicians; some of the musicians are painters. We present a computer model that implements the latest account of syllogisms, which is based on the theory of mental models. We also report four experiments that were designed to test this account. Experiments 1 and 2 examined the strategies revealed by the participants' use of paper and pencil as aids to reasoning. Experiment 3 used a new technique to externalize thinking. The participants had to refute, if possible, putative conclusions by constructing external models that were examples of the premises but counterexamples of the conclusions. Experiment 4 used the same techniques to examine the participants' strategies as they drew their own conclusions from syllogistic premises. The results of the experiments showed that individuals not trained in logic can construct counterexamples, that they use similar operations to those implemented in the computer model, but that they rely on a much greater variety of interpretations of premises and of search strategies than the computer model does. We re-evaluates current theories of syllogistic reasoning in the light of these results.

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This study concerned the role of gestures that accompany discourse in deep learning processes. We assumed that co-speech gestures favor the construction of a complete mental representation of the discourse content, and we tested the predictions that a discourse accompanied by gestures, as compared with a discourse not accompanied by gestures, should result in better recollection of conceptual information, a greater number of discourse-based inferences drawn from the information explicitly stated in the discourse, and poorer recognition of verbatim of the discourse. The results of three experiments confirmed these predictions.

We investigated the syllogistic reasoning of children 9-10 years of age, adolescents, and adults. Their performance on five tasks that theoretically might measure components of such reasoning was examined: the interpretation of quantifiers such as some and all; the referential integration of assertions; the search for counterexamples to generalizations; the perception of identical shapes within figures; and the processing capacity of working memory. Syllogistic ability improved reliably with age, though even the youngest subjects were able to draw valid conclusions well above chance to one-model syllogisms. Performance on two of the component tasks also improved reliably with age: the detection of identities, and the capacity of working memory. Multiple regressions showed that performance on these two tasks also accounted for some of the variance in syllogistic reasoning. Performance on the other three tasks was at about adult level by the age of 9. We accordingly examined performance with a group of 7-year-old children and discovered that they also performed at better than chance with one-model syllogisms. Our results support three main conclusions: young children are capable of syllogistic reasoning (contrary to the claims of Inhelder & Piaget, 1964); there is a significant development of ability from childhood to adulthood; and it is possible to identify some of the major components of this improvement. Development of the ability to reason How could children who do not know how to reason validly acquire the ability to do so? This question is deeply puzzling-so puzzling, in fact, that none of the three sorts of answers to it made by psychologists is viable (see Johnson-Laird, 1990). The first sort of answer is that children acquire logical ability through the normal operations of conventional learning. Given some existing ability, children might learn other procedures by the operations of generalization and specialization (Falmagne, 1980), but it is probably impossible for such mechanisms to yield the concept of validity or procedures to establish it. The second sort of answer, Piaget's, is that intellectual development is governed by an automatic tendency to self-regulation that he called equilibration. Each new equilibrium is the outcome of compensatory reversible operations, but each is also an occasion for further cor