John Pollock viewed his theories of defeasible reasoning as central to his epistemology, and indeed, as his most important achievement.  But this work is not generally well understood, is sometimes regarded as inaccessible, and is almost entirely neglected within philosophy.  In this talk, John Horty will reconstruct Pollock's two central theories, from 1987 and from 1994, in a uniform framework and from a uniform point of view, and then reflect on these theories from the standpoint of more recent work on argument-based defeasible reasoning.