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The mental model theory postulates that reasoners build models of the situations described in premises. A conclusion is possible if it holds in at least one model of the premises; it is probable if it holds in most of the models; and it is necessary if it holds in all of the models. The theory also postulates that reasoners represent as little information as possible in explicit models and, in particular, that they represent only information about what is true. One consequence is that there should be a category of illusory inferences: they will have conclusions that seem obvious, but that are wholly erroneous. Experiment 1 established the existence of such illusory inferences about probabilities. Overall, 88% of the intelligent adult subjects chose as more probable an outcome that was impossible for at least one of the illusory problems. Experiment 2 corroborated the phenomenon and showed that illusory inferences include a wide variety of problems. Finally, the paper argues that current theories based on formal rules of inference are unlikely to be able to explain the illusions.

Reasoning about possibilities is fundamental in daily life and inartificial intelligence. It is formalized in modal logics, of whichthere are infinitely many. Two experiments showed thatindividuals make inferences that are parsimonious aboutpossibilities, and that they reject conclusions referring topossibilities that the premises do not support. Both sorts ofinference contravene modal logics, i.e., the simplest system ofmodal logic and the infinite number of systems based on it.

Many theories of reasoning and many experiments presupposethat human ability is stable over time, and so people usuallydraw the same conclusion from the same premises. The as-sumption has hitherto had little or no empirical investigation.We therefore analyzed a study in which 20 participants drewtheir own conclusions to the 64 sorts of syllogisms on twooccasions separated by roughly a week. We report the na-ture of the changes in the participants’ conclusions includingtheir spontaneous improvement in logical accuracy, and use amodel-based program, mReasoner, to explain the results.

The mental model theory postulates that reasoners build models of the situations described in premises, and that these models normally make explicit only what is true. A computer program revealed an unexpected consequence of the theory: it predicts that certain inferences should have compelling but erroneous conclusions. Two experiments corroborated the existence of such illusions in inferences about what is possible given quantified assertions, such as 'At least some of the plastic beads are not red.' Experiment 1 showed that, as predicted, participants erroneously inferred that impossible assertions were possible, and that possible situations were impossible, but they performed well with control problems. Experiment 2 demonstrated the existence of similar illusions in inferences from dyadic assertions, e.g. 'All the boys played with the girls'.

This article presents a theory of how individuals detect whether descriptions of an entity are consistent or inconsistent. The theory postulates that individuals try to construct a mental model of the entity in which all the propositions are true. If they succeed, they infer that the description is consistent; otherwise, they infer that it is inconsistent. We report three experiments that corroborated the theory. Experiment 1 confirmed that evaluating consistency is easier when an initial model suffices than when reasoners have to find an alternative model. Experiment 2 established the occurrence of illusory inferences about the properties of entities. Experiment 3 showed that the illusions correspond to mental models of the assertions, even when these models are wrong because they fail to represent what is false.

Four experiments examined the strategies that individuals develop in sentential reasoning. They led to the discovery of five different strategies. According to the theory proposed in the paper, each of the strategies depends on component tactics, which all normal adults possess, and which are based on mental models. Reasoners vary their use of tactics in ways that have no deterministic account. This variation leads different individuals to assemble different strategies, which include the construction of incremental diagrams corresponding to mental models, and the pursuit of the consequences of a single model step by step. Moreover, the difficulty of a problem (i.e., the number of mental models required by the premises) predisposes reasoners towards certain strategies. Likewise, the sentential connectives in the premises also bias reasoners towards certain strategies, e.g., conditional premises tend to elicit reasoning step by step whereas disjunctive premises tend to elicit incremental diagrams. Keywords: Strategies; Reasoning; Mental models

Experiments conducted on the influence of diagrams on deductive reasoning with double disjunctions reveal that disjunctive possibilities render thinking more difficult. The use of a suitable diagram that aids reasoners in the examination of all explicit possibilities, attenuates this problem. Subjects react around 35 seconds slower and aim at almost 30% less valid conclusions, when asked to arrive at conclusions based on diagrams instead of verbal premises.

Presents information on a study of a theory of modal reasoning. Predictions of the theory which are corroborated experimentally; Description on the mental model theory of modal reasoning; Key interaction in modal reasoning.

Consciousness and the Computational Mind. RAY JACKENDOFF. MIT Press, Cambridge, MA, 1987. xvi, 356 pp., illus. $27.50. Explorations in Cognitive Science, vol. 3. A Bradford Book. In the early years [...]