Valid Ad Hominem Arguments in Philosophy: Johnstone's Metaphilosophical Informal Logic

Abstract

This is a critical examination of Johnstone's thesis that all valid philosophical arguments are ad hominem. I clarify his notions of valid, philosophical, and ad hominem. I illustrate the thesis with his refutation ofthe claim that only ordinary language is correct. r discuss his three supporting arguments (historical, theoretical, and intermediate). And r criticize the thesis with the objections that if an ad hominem argument is valid, it is really ad rem; that it's unclear how his own theoretical argument can be ad hominem; that if an ad hominem argument is really valid, it would have to be based on the proponent's own assumptions; and that the thesis is not true of philosophical arguments that are constructive rather than critical.