Introduction

The aim of this chapter is a critical examination of the thesis that valid philosophical arguments are ad hominem. This thesis was advanced by Henry W. Johnstone, Jr. and constitutes a highly original contribution, a brilliant idea, and a constant theme of his half a century of philosophical effort. In general, his work was a pioneering effort in the informal logic of philosophical argument and included other related themes, such as metaphilosophy and the role of rhetoric and of formal logic in philosophy. In focusing on this thesis, I do so because it is probably his key contribution and is emblematic of both the rest of his work and of the informal logic of philosophy. I shall first discuss several clarifications, then a concrete illustration, then some supporting arguments, and finally several objections.

Clarifications

The thesis can be expressed in several ways: that “all valid philosophical arguments are ad hominem” (PA81); that in philosophy only ad hominem arguments are valid (PA3; VR56); that the validity of philosophical arguments lies in the property of being ad hominem (PA57–92); that ad hominem argument “is the only valid argument in philosophy” (VR134); and that in order to be valid philosophical arguments must be ad hominem.