Galen on the Signs of Disease

Abstract This chapter discusses how Galen interacted with the historically crucial Hippocratic text Prognostic in setting out the basics of the doctor’s clinical methodology and approach to diagnostics. It places alongside each other the diagnostic and prognostic model of the Hippocratic text and Galen’s response to it, focusing on Galen’s definition of what constitutes a sign (sēmeion). The chapter analyses Galen’s account of the “power” (dunamis) of a sign; of how this can be measured; of how different kinds of signs can be compared; and of the relationship between a sign (sēmeion) and a tekmērion—an “evidence” or “valid sign,” where the former is taken to be a “weaker” version of the latter.