219 Croatian Journal of Philosophy Vol. VI, No. 17, 2006 Logic, Reasoning and the Logical Constants PASCAL ENGEL Université Paris Sorbonne and Institut Jean Nicod Introduction Consider the three questions: (a) how do we reason? (b) how ought we to reason? (c) what justifies the way we ought to reason? Question (a) is a descriptive one: it calls for an account, presumably a psychological one, of how humans reason, a theory of their reasoning abilities and of their reasoning performances. Question (b) is normative: it calls for a theory of how we evaluate whether a reasoning is good or bad, correct or incorrect, valid or invalid. Usually this role is devoted to logic. Question (c) is, so to say, meta-normative; it calls for the justifica- tion of our norms and standards of reasoning, possibly against other norms. On many accounts, the answers to these three questions differ wide- ly, and on many accounts they must do so. On the classical view of logic as a normative discipline, there is a strong distinction between the way we reason actually and the way we should reason, and the attempt to derive the latter from the former, is considered as the most obnoxious fallacy about the nature of logic: psychologism. Today’s psychologists of reasoning, however, guard themselves against this fallacy. They are all the more suspicious of it that they find that there is a large gulf between our actual reasoning practices and logic as the theory of valid reason-