On interpreting reasoning data — A reply to Van Duyne

In a previous article (Evans, 1972a) it was argued that theorists had misinterpreted data in reasoning experiments by assuming that subjects were responding to the logical structure of the problems. Instead it was proposed that results should be interpreted in relation to two kinds of ‘non-logical’ variables, those which affect the interpretation of the sentences forming the propositions, and those which affect the reasoning operations involved. One such operational variable discussed was ‘matching bias’ or the tendency for subjects to select values named in logical rules for testing hypotheses, irrespective of the logical consequence of such selections. This has been demonstrated by manipulating the presence of negative components in conditional rules (Evans, 1972b, Evans & Lynch, 1973). Van Duyne (1973, 1974) in criticising my approach to these problems has concentrated on the problem of ‘matching bias’ as an explanatory concept. His criticisms may be summarized as follows: (i) The matching bias effect lacks empirical generality (ii) My psychological explanations of the effect are vacuous (iii) The postulation of a ‘non-logical’ matching bias is inconsistent with introspective protocols which show that “in these experiments subjects are trying to reason correctly” (Van Duyne, 1973, p. 240) In support of the explanatory power of the matching bias hypothesis it should be recalled that it is the only explanation of Wason’s well known ‘selection task’ (for detailed discussion see Wason & Johnson-Laird, 1972) to have been deduced from an entirely independent reasoning situation (Evans, 1972b) and subsequently predicted and observed on the selection task (Evans & Lynch 1973). It is true that matching bias does not generalize to problems with realistic materials, at least so far as the selection task is concerned, since in these circumstances subjects tend to produce the logically correct responses, (e.g., Wason & Shapiro, 1971, Johnson-Laird, P. Legrenzi &, M. Legrenzi, 1972), presumably because there is a strong semantic basis for interpretation. Van Duyne correctly states that the effect is also not observed on abstract tasks when disjunctive rules are used. This is rather puzzling but the introduction of negative components produces sentences which are so unnatural as to be almost impossible for subjects to interpret (see Evans 1972a). I do, however, have some data to show that the