The argument advanced in Plato's dialogue Parmenides against the doctrine of forms . Suppose we start with the collection of large things. Now suppose that there is some form that they all share: the form of largeness. We now have a new collection, namely all the original things plus the form of largeness. So there must be a further form uniting all the members of this collection, and this launches us on an infinite regress. Aristotle uses the example of men, and the argument gains its title from him.
Philosophy dictionary. Academic. 2011.