The historical transition from the Hippocratic Writers and Aristotle to Galen has been depicted in various ways. This book’s emphasis has been to examine treatments of blood through the lens of various senses of phusis. Using the methodology of twenty-first-century philosophical logic and philosophy of science, the intent has been to show how these writers make important contributions to the timeless conundrums that face all philosophers of science. For our purposes in this volume, the next writers to discuss are Diocles of Carystus and Praxagoras as setting out an initial program that will set the stage for third-century BC biomedical writers.1 On the one hand, both of these writers fit in with the Critical Empiricism program of Aristotle that tended toward D-◊.2 These writers’ acceptance of a realistic phusis1 context that could be discovered and described caused others in the Hellenistic period to depict this group of writers as Dogmatists (dogmatikoi) or Logical/Rationally based Physicians (logikoi).3 Both epithets have something to recommend them. This volume will use the term “Dogmatist,” though what is most important in this nominal baptism is that according to our chart of modality set out in Chapter 2 of this volume, being logical means that one is probably situated at D-◊ with a desire to be at D-□ (only those nasty individualistic details get in the way).4 One of the reasons that it is difficult to pinpoint Dogmatists as exactly as the Empiricists or Methodists is because the Dogmatists were a less coherently recognizable group than either the Empiricists or the Methodists. This accounts for the Dogmatist span from D-□ to D-◊.