INTRODUCTION

Responding to Harvey's theories about the circulation of the blood, Dr. Diafoirus argues (a) that no such theory was taught by Galen, and (b) that Harvey is not licensed to practice medicine in Paris. Plainly there is something wrong with a response of this sort, however effective it may prove to be in swaying an audience. For either or both of (a) and (b) might well be true without Harvey's theory being false. So Diafoirus's argument can serve only to divert discussion from the real question to irrelevant sideissues. The traditional term for such diversionary debating tactics is “fallacy of relevance.”

In recent years this tradition has come to be used in a quite untraditional sense among followers of N. D. Belnap, Jr., and the late A. R. Anderson. (All citations of these authors are from their masterwork Anderson and Belnap (1975), and are identified by page number.) According to these selfstyled “relevant logicians,” it is items (IA) and (IIA) in Table 13.1 that constitute the archetypal “fallacies of relevance.” (In the table ∼, &, and ⋁ stand for truth-functional negation, conjunction, and disjunction, respectively.) These forms of argument, say Anderson and Belnap, are “simple inferential mistake[s], such as only a dog would make” (p. 165). The authors can hardly find terms harsh enough for those who accept these schemata: they are called “perverse” (p. 5) and “psychotic” (p. 417).