The first and most important step into the Peripatetic study of living beings is the observation that life takes many forms. In the sublunary world, it takes the form of plant and animal life (with human life as a special kind of animal life). When Aristotle and Theophrastus speak of animals and plants, they never assume that they are a single form of life. This is confirmed by what we read at the outset of the Meteorology, where Aristotle outlines an ambitious research program that ends with separate yet coordinated studies of “animals and plants.” Whether there is unity, and how much unity there is, in these two studies remains an open question at the outset of the Meteorology. But when we look at the two corpora of writings that Aristotle and Theophrastus have left on the topic of animals and plants, we see that the unity they are able secure is limited. Last but not least, this chapter shows that the study of the nutritive soul advanced in Aristotle’s De anima cannot secure unity within the study of animals and plants.

This chapter addresses an interpretive question about why Aristotle identifies generation, growth, and nourishment as the three distinct functions or activities of nutritive soul. Scholars typically try to explain this by appealing to the shared goal of these activities, though there is no consensus about what that goal is: Does Aristotle think that generation is a way of keeping oneself alive (and thus that the shared goal is self-maintenance), or is nourishment really a quasi-generative activity (and thus that the shared goal is “form (re)production”)? Rather than taking that approach, Gelber offers a different but complementary way of accounting for the unity of these activities, by focusing on the continuity of their shared physiological basis. As it is argued here, the fact that these biological processes form a continuous cycle stems from Aristotle’s adherence, in his biological theory, to principles from his hylomorphic metaphysics. Attending to the details in works such as Generation of Animals that focus on the mechanisms underlying generation, growth, and nourishment, it is shown how we can construct a coherent account of the unity of the three nutritive soul activities.

The basis for terrestrial life in Aristotle’s biology is the nutritive process by which living things (plants and animals) produce and maintain their uniform parts and the organs made of these uniform parts. The nutritive process is thus extremely general, across all kinds. But it is also general in being present in all stages of the life cycle. Thus, it starts with the beginning of life, increases as the living thing grows, and subsides and is extinguished with the end of life. This variation in quantity is possible because there are two sides to the process, one is the heat necessary for “cooking” food into the parts of the living thing, and the other is the soul which informs this cooking. While the heat can be more or less, the soul is either there or not. The process of feeding (trephein) is shown to be Aristotle’s single sufficient and necessary condition for all natural life. It is the assimilation of food (trophê) to the living thing in question, an activity which the soul performs, thus producing and maintaining the living body, using the body’s heat as an instrument to work on food.

Lennox explores the role of cooling in the regulation of natural heat and the preservation of life with special interest in methodological questions about how Aristotle arrived at his views about the critical role of cooling in the lives of blooded animals and why he insists that both the brain and the lungs are involved in moderating the animal’s heat. Lennox concludes that Aristotle was somewhat perplexed by the brain, and that his changing views about its presence in the cephalopods may be an indication of that perplexity.