Galen explicitly states that, using theoretical reasoning in conjunction with empirical evidence, progress in knowledge is possible. At the same time—a perception typical within Graeco-Roman culture—he regards the pathway from the “ancients”, in particular Hippocrates, to the moderns as in general a downward one, and “more recent”, in relation to medical or scientific authors, is usually a term of disapprobation. He does, however, claim that progress in relation to the ancients is possible, and indeed that he has achieved it, in two chief senses. One is that, for example in anatomy, he has made certain specific discoveries unknown to his predecessors; the other, more substantial in his presentation, is the project of giving solid demonstrative form to propositions which (according to Galen) were known to the ancients, but either stated by them without demonstration, or actually omitted from their writings (Opt. Med. 4, 34; Hankinson 1994a).