Andrea Falcon argues that Aristotle considered natural science to be a coherent, systematic, and unified program while at the same time maintaining that the object of the study consists of a two-world system based on essentially different and incompatible substances. He sums up his model with the slogan, “unity without uniformity.” This short but rich monograph wrestles with important issues in Aristotelian philosophy of science, epistemology, and cosmology with some attention to psychology and biology. The issues at stake are significant: (...) To what degree is Aristotle’s science of nature programmatic? How can Aristotle maintain a single physical science if his universe rests on two mutually exclusive material substances that are spatially distinct, unmixed, and in many ways opposites? And finally, at what point does Aristotle limit his inquiry due to the lack of perceptual data regarding celestial phenomena? While answering these questions, Falcon also offers an explanation of why subsequent philosophers, including many members of the Lyceum, rejected his position on the celestial simple body, and how Stoic cosmology benefited from the perceived difficulties in Aristotle’s position.Two basic ideas drive the investigation: First, that Aristotle’s science of nature is a single, unified inquiry and not simply a collection of. (shrink)