We present an integrated model for the understanding of and the reasoning from conditional statements. Central assumptions from several approaches are integrated into a causal path model. According to the model, the cognitive availability of exceptions to a conditional reduces the subjective conditional probability of the consequent, given the antecedent. This conditional probability determines people's degree of belief in the conditional, which in turn affects their willingness to accept logically valid inferences. In addition to this indirect pathway, the model contains a direct pathway: Availability of exceptional situations directly reduces the endorsement of valid inferences. We tested the integrated model with three experiments using conditional statements embedded in pseudonaturalistic cover stories. An explicitly mentioned causal link between antecedent and consequent was either present (causal conditionals) or absent (arbitrary conditionals). The model was supported for the causal but not for the arbitrary conditional statements.

Previous research (Oberauer & Wilhelm, 2000) has shown an inherent directionality between the two terms linked in premises of typical deductive reasoning tasks. With three experiments we investigated the effect of inherent directionality on the time to integrate two premises and for the derivation of a conclusion. We varied figure (i.e., order of terms in the premises) and direction of inference (i.e., order of terms in the conclusion) in deduction tasks from various domains (propositional reasoning, syllogisms, spatial, temporal, and linear order reasoning). Effects of figure on premise reading times varied with the directionality of the relations. Effects of direction of inference reflected the same directionality for a subset of relations. We propose that two factors are jointly responsible for a large part of observed directionality effects in premise integration: the inherent directionality of relational statements and a general advantage for a given-new order of terms in the second premise. Difficulty of deriving a conclusion is affected by the directionality or relations if and only if the relation is semantically asymmetric, so that the directionality must be preserved in the integrated mental model.

In the standard three-term spatial reasoning task, the reasoner receives a pair of spatial-relational premises, P1 and P2, in verbal form-for example, The knife is to the left of the vase. The vase is to the left of the glass. Then he/she is asked for the spatial relation not explicitly asserted; in the example above, that is the relation between the knife and the glass. 1 How do people accomplish this task? Huttenlocher (1968) suggested that people construct a spatial image of the described layout and then read off the unmentioned relation from that image. Accordingly, the main task is to construct an integrated representation of the spatial layout, a process that we refer to as premise integration: "In explaining the mental processes of the problem solver, one may deal only with the issue of how information from the two premises is combined. . . . This process is traditionally what is meant by reasoning, as separable from merely understanding the individual premises" (Huttenlocher & Higgins, 1971, p. 487). To characterize the reasoning task in this wayas language understanding beyond the level of single sentences-is to conceive of it as text comprehension. We would then expect premise integration to be guided by principles of language comprehension.Huttenlocher 's (1968) idea that the reasoner operates on a representation of the described layout rather than on a representation of the description of the layout has been further developed by Johnson-Laird (1983 in his mental model theory. Within this framework, an initial mental model is constructed on the basis of the first premise, and then the new element mentioned in the second premise is integrated into the initial model. Thus, premise integration should be especially sensitive to properties of the second premise. The present work is an attempt to bring ideas from reasoning and from language comprehension research within the mental model framework. In particular, we tested two linguistically motivated principles of premise integration, the given-new principle derived from work on discourse pragmatics, and the relatum ϭ given principle developed in the tradition of model theories of reasoning. The Given-New StrategyOn the basis of linguistic analyses (e.g., Chafe, 1970 2 ; Halliday, 1968), Clark and Haviland (1977) postulated the given-new strategy for language comprehension. Integrating information of the current sentence with previous information is performed in three steps: (1) identifying the given information of the current sentence, (2) finding an antecedent for the given information, and (3) attaching the new information to the antecedent. Since the first two steps are carried out as soon as the given information is encoded, mentioning given information before new information speeds up integration. On the other hand, mentioning new information initially in a sentence increases memory load because it requires holding the new information in abeyance until the given information becomes available. On the basis of these assumptions, the given-new strategy...

We report two experiments testing a central prediction of the probabilistic account of reasoning provided by Oaksford and Chater (2001): Acceptance of standard conditional inferences, card choices in the Wason selection task, and quantifiers chosen for conclusions from syllogisms should vary as a function of the frequency of the concepts involved. Frequency was manipulated by a probability-learning phase preceding the reasoning tasks to simulate natural sampling. The effects predicted by Oaksford and Chater (2001) were not obtained with any of the three paradigms.

This article presents a cross-linguistic study of semi-spontaneous data obtained from an