This paper argues for a reinterpretation of Aristotle s concept of an enthymeme and also his wider informal logic in terms of arguments that are defeasible. They are represented by forms of argument that are called argumentation schemes, considered to be similar to forms of argument found in deductive logic, but different from the foregoing in virtue of their being defeasible. Indeed, the most interesting schemes have been put forward as a helpful way of characterizing structures of human reasoning that have proved troublesome to model deductively. The paper sheds new light on Aristotle s topics and how to define enthymeme . If the traditional definition of an enthymeme in logic accepted for over two thousand years is a misnomer, the question is raised whether we ought to redefine it as a defeasible argumentations scheme or leave things as they are.