Abstract
Diogenes subscribes to a principle that, roughly, causal interaction and change require a certain sort of uniformity among the relata. Attending to this principle can help us understand Diogenes's relationship to the superficially similar Anaximenes without insisting, as some do, that Diogenes must be consciously responding to Parmenides. Diogenes is distinctive and philosophically interesting because his principle combines two senses of ‘archê’ (principle, starting-point), namely, the idea of source or origin and that of underlying (material) principle, and gives the rudiments of an argument for associating the two, by which Aristotle may have been influenced. Diogenes’s principle and its deployment in biological explanations thematized a concern that Aristotle at least partially shared, and which led him to appeal, as Diogenes is said to have done, to pneuma (breath, air).