ABSTRACT
Johnson-Laird and his associates (e.g., Byrne & Johnson-Laird, 1992; Johnson-Laird, 1992, 1993; Johnson-Laird & Byrne, 1991; Johnson-Laird, Byrne, & Shaeken, 1992) recently have applied their mental-models theory of deductive reasoning to the conditional syllogisms. The four conditional syllogisms of standard logic each have a major premise of the form If p then q, with either the antecedent affirmed or denied, or the consequent affirmed or denied, as a minor premise (Table 14.1). Modus ponens (MP), with p as its minor premise, has q as its valid conclusion, and modus tollens (MT), with not q as its minor premise, has not p as its valid conclusion. Neither the affirmation of the consequent (AC), with q as its minor premise, nor the denial of the antecedent (DA), with not p as its minor premise, leads to any valid conclusion concerning its corresponding term, although people often accept the fallacious inferences of p and of not q, respectively. People rarely make any determinate responses on any of these problems except q on MP, p on AC, not q on DA, and not p on MT, and we shall refer to these as the expected determinate responses.
