Aristotle on the Souls of Animals
With his teacher Plato, Aristotle was the most important thinker in the Western philosophical tradition. In the Middle Ages, Dante called Aristotle "the master of those who know," and Thomas Aquinas referred to him simply as "the philosopher." But Aristotle was not only a philosophical genius. Before Darwin came along more than 2,000 years later, Aristotle was also the greatest biologist in Western history. These two statuses were not independent of one another. Aristotle the biologist is always in the background of his work as a philosopher, and the reverse is true as well. For example, in his metaphysical inquiry into the nature of being, Aristotle regards living organisms as the key examples of things that have being in the primary sense of the word. In his theory of knowledge, he interprets perception and cognition as essentially animal activities of discriminative response to the surrounding world. And in his psychology, he regards the soul as the principle of living things, and the mind as a faculty of highly developed forms of animal life. The productive cross-fertilization of philosophy and biology in Aristotle's work led him to develop a dynamic conception of the world in which entities move from potentiality to actuality in the process of realizing the ends, or goals, that in fact make them what they are. This is the famous teleological conception of the cosmos which such early modern thinkers as Galileo, Newton, Bacon, Descartes, and Spinoza rejected in its degenerate late medieval form. In spite of the modern scientific and philosophical rejection of teleology however, there are compelling arguments to be made that living beings at least cannot be properly understood apart from a consideration of the way in which they tend to realize ends internal to themselves. From a certain restricted point of view, it is possible to view living things as machines. Their bodies can be analyzed into parts that move one another in ordered fashion, just as the gears, levers, wheels, and pulleys of humanly produced machines link in elaborate causal sequences. Aristotle was familiar with the pattern of broadly materialist explanation from the work of the pre-Socratic natural philosophers, including the atomists Leucippus and Democritus, and he himself suggested even more narrowly mechanistic versions of materialist explanation in some of his biological writings, where he pursues analogies between the functioning of organic bodies and that of the self-moving "puppets" and other mechanical automata of his period. But while such explanatory approaches can tell us how organic bodies work, they cannot tell us why they work the way they do. In examining the operation of a machine, we are able to ignore the "why" question only because we take for granted the fact that it can be answered by appealing beyond machine's functioning to the purposes that its creator attempted to realize by making it and its users by employing it But in the investigation of living things, there are no such external purposes. The flourishing of the organism as the specific kind of thing that it is is the end all of its material processes pursue. In the case of biological inquiry and explanation, "how" questions and "why" questions are inseparable. But what concretely does it mean to say that the purposes living things seek to realize are internal to them? How does teleology cast light on the non-mechanistic processes involved in being alive? What does Aristotle mean in detailed terms when he says that organisms have souls. These are the questions that Aristotle addresses in the following excerpts from his biological and psychological writings.
Aristotle: On the Parts of Animals