 The theories of Heracleides of Pontus (4th c. BCE) and Asclepiades of Bythnia (2nd c. BCE) are sometimes likened to atomism (Gottschalk 1980; Vallance 1990). Both—a pupil of Plato, and a medical theorist—are said to have posited the existence of corpuscles they call anarmoi onkoi, likely some kind of partless masses: the precise meaning is uncertain. Although the theories of Asclepiades in particular are often assimilated to atomism, it may be that Galen’s characterization of this view is polemical, and that Asclepiades’ particles are capable of division. Galen is the source for a distinctive argument against the idea that atoms were alike in substance, based on the Hippocratic idea that organisms composed of a single substance would not be able to experience sensations like pain (Leith 2014). Ironically, Galen’s theory of the four elements was sometimes interpreted as an atomist theory by medieval sources (Langermann 2009).