This chapter argues that the cosmological doctors arose as the result of a much wider realignment in Classical Greek medicine. As some doctors grew increasingly concerned about the many variables that can change from one case to the next, they rejected older forms of diagnostic handbooks in favor of new methods for organizing medical knowledge. We see this anxiety over individual differences not only in the works of the cosmological doctors but also in texts such as On Regimen in Acute Diseases, Prognostic, Airs Waters Places, and the seven books of Epidemics. In all of these texts, medical inquiry is defined, quite generally, as a search for commonalities. Doctors in this period were gathering together multiple accounts, noting the similarities and differences between those accounts, and isolating high-level generalizations that can unite and govern them all. Although the cosmological doctors took their search for commonalities farther than some of their contemporaries might have been willing to follow, they nevertheless responded to the same pressures that transformed nearly all the medical literature that survives from this period.

This chapter gives an overview of the problems raised by the concept of motion in the period investigated – specifically, its apparent integration of Being and non-Being, and its combination of Time and Space. It then discusses the central notions employed in the present project: the criteria or standards established for philosophical inquiry (the principles of non-contradiction and of sufficient reason, and a criterion termed “rational admissibility”) and the roles of logic and mathematics in establishing natural philosophy. This chapter lays out broad outlines, systematic and historical, of the issues to be discussed in detail in the ensuing chapters, each of which will deal with one thinker or one school. Thus this opening chapter will serve as a first orientation for the project as well as a reservoir for consultation if questions concerning the basic concepts employed arise during the reading of the whole book.