Isti *

Oakhill, J., Johnson-Laird, P.N., and Gornham, A., 1989. Believability and syllogistic reasoning. Cognition, 31: 117-140. In this paper we investigate the locus of believability effects in syllogistic reasoning. We identify three points in the reasoning process at which such efsects could occur: the initial interpretation of premises, the examination of alternative representations of them (in all of which any valid conclusion must be true), and the @filtering” of putative conclusions: The effect of beliefs at the first of these loci is well established. In this paper we report three experiments that examine whether beliefs have an effect at the other two loci. In experiments 1 and 2 subjects drew their own conclusions from syllogisms that suggested believable or unbelievable ones. In the third experiment they evaluated conclusions that were presented to them. The data show that beliefs both affect the examination of alternative models and act as a filter on putative conclusions. We conclude by showing how some types of problem and some problem contents make the existence of alternative models more obvious than others. Logicians draw a distinction between the validity of an inference and the truth of its premises and conclusion. Although a false conclusion can never *Requests for reprints should be addressed to: Jane Oakhill, Laboratory of Experimental Psychology, University of Sussex, Brighton BNI 9QG. U.K. OOlO-0277/89/$7.70