In this study, we investigated the possibility that a response bias might be responsible for the typical pattern of responding observed when people reason about artificial relationships, especially set inclusions. Experiment 1 provided strong evidence for the proposed bias, since subjects tended to respond as if an unspecified relationship were symmetrical and increasingly intransitive over inferential distance. However, Experiment 2, using extended syllogisms, showed that not all relationships lead to such responding. Although the majority of the quantified relationships were responded to as if they were symmetrical, most were also regarded as transitive. Thus, the response bias idea, although of some interest, cannot provide a complete explanation of performance on these tasks.In the literature on reasoning, there is a longstanding dispute between the rationalists and nonrationalists. The rationalists believe that reasoning is inherently logical and that errors can be explained by misinterpretation of the premises, whereas the nonrationalists believe that errors can be attributed to nonlogical response biases.In the present paper, we attempt to make a contribution to this dispute by exploring the existence of a nonlogical response bias that may explain performance on a variety of reasoning tasks involving artificial relationships. The bias in question is a tendency to assume that any relationship is (1) symmetrical and (2) increasingly intransitive over inferential distance. This can be illustrated best by considering the schematic relationship A-B, B-C, C-D, where A, B, C, and D are entities and "-" depicts any relationship connecting them. To say that the relationship is symmetrical means that subjects will assume that the relationship holds both ways, so that, for example, B-A is true as well as A-B. To say that the relationship is intransitive implies that transitive inferences will not tend to be accepted as true: Subjects will tend not to accept conclusions such as A-C or B-D. To say that the relationship is increasingly intransitive over inferential distance means that as the number of steps required to make a transitive inference increases, subjects will be less likely to accept the inference. Thus, in the above example, A-D would be less likely to be accepted than A-C or B-D.Although such a bias has not been discussed previously in the literature, there is in fact a range of evidence consistent with it. One line of evidence comes from Tsal (1977), who gave subjects problems involving a relationThe authors thank Ray Burke for his assistance in generating the experimenta materials for Experiment 2. Requests for reprints should be sent to S. E. Newstead. Department of Psychology. Plymouth Polytechnic. Drake Circus. Plymouth. Devon PL4 8AA, England.ship among four people, but the actual nature of the relationship was not specified (it was denoted by a short line, as in the schematic example above). The majority of subjects (72 %) assumed that the relationship was symmetrical, and 76% assumed it was intran...