There are two views of the ad hominem argument found in the textbooks and other traditional treatments of this argument, the Lockean or ex concessis view and the view of ad hominem as personal attack. This article addresses problems posed by this ambiguity. In particular, it discusses the problem of whether Aristotle's description of the ex concessis type of argument should count as evidence that he had identified the circumstantial ad hominem argument. Argumentation schemes are used as the basis for (...) drawing a distinction between this latter form of argument and another called argument from commitment, corresponding to the ex concessis argument. (shrink)