Aristotle and the Science of Nature: Unity without Uniformity (review)

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 relatively independent treatises. Secondly, that although the science is unified (methodologically, thematically, ontologically, and epistemologically), the natural world is not uniform. Falcon uses the prologue to the Meteorology to establish the unity of Aristotle’s project. Reading the passage normatively, Falcon concludes that Aristotle prescribed an ideal sequence for the study of natural science beginning with the Physics, followed by the De Caelo, De Generatione et Corruptione, and Meteorology, and concluding with the zoological works. This sequence is justified by the belief that inquiry must mirror the direction of causal explanation in nature. Surprisingly, De Anima is not part of this program.

Chapters two and three present a careful analysis of the logic of the simple bodies and simple motions, showing why Aristotle held each of the five elements to be necessary substances and why there can only be two kinds of natural motion. Aristotle’s cosmology is presented not as creative speculation, but as deductive inferences drawn from basic principles. The result is a two-world system that is unlike Plato’s two-world system, which struggles to tell a causal story. Falcon also emphasizes the “crucial, though too often neglected truth: the celestial motion that is naturally performed by the celestial bodies is not the circular motion that is naturally performed by the celestial simple body” (83). This position requires Aristotle to exploit the commonly-held belief that the celestial bodies are alive and intelligent. Celestial bodies operate with voluntary motion which is not “non-natural” since the principle of motion comes from within, and thus is not forced.

In the fourth and final chapter, Falcon addresses the problem of the epistemic limits of this unified but not uniform science of nature. This includes a return to issues central to the De Anima. Wisely, the question of the nature of the unmoved mover is avoided; but Falcon continues to raise questions concerning the cognitive status of celestial bodies. Although, alive, intelligent, and happy, celestial bodies do not have phantasiai since they have no organs of sense. Their motion seems to be connected to desire; however, desire usually entails sensory provocation. How does one make sense of this? In contrast to sublunary animals, which navigate their environment with progressive motion guided by sensory awareness, the celestial intelligences do not navigate the heavens; instead they move in accordance with rational desire.

We have now reached (or exceeded) the boundary of what can be known about the heavens. Falcon concludes by examining the epistemic limitations in Aristotle’s cosmology. Aristotle recognizes that the natural philosopher is severely compromised due to the remoteness and inaccessibility of the celestial bodies. However, we cannot simply concede ignorance and refrain from studying the celestial realm if the direction of inquiry and...