On the Soul (Greek: Περὶ Ψυχῆς, Peri Psychēs; Latin: De Anima) is a major treatise written by Aristotle c. 350 BC classifying organisms' souls by their operations. In it, he alleges plants have the capacity for nourishment and reproduction, the minimum that must be possessed by any kind of living organism. Lower animals have, in addition, the powers of sense-perception and self-motion (action). Humans have all these as well as intellect. Aristotle holds that the soul (psyche, ψυχή) is the form, or essence of any living thing; it is not a distinct substance from the body that it is in. It is the possession of a soul (of a specific kind) that makes an organism an organism at all, and thus the notion of a body without a soul, or of a soul in the wrong kind of body, is simply unintelligible. (He argues that some parts of the soul—the intellect—can exist without the body, but most cannot.) In 1855, Charles Collier published a translation titled On the Vital Principle. George Henry Lewes, however, found this description also wanting.
Division of chapters The treatise is divided into three books, and each of the books is divided into chapters (five, twelve, and thirteen, respectively). The treatise is near-universally abbreviated "DA", for "De anima", and books and chapters generally referred to by Roman and Arabic numerals, respectively, along with corresponding Bekker numbers. (Thus, "DA I.1, 402a1" means "De anima, book I, chapter 1, Bekker page 402, Bekker column a [the column on the left side of the page], line number 1.)
Book I DA I.1 introduces the theme of the treatise; DA I.2–5 provide a survey of Aristotle’s predecessors’ views about the soul
Book II DA II.1–3 gives Aristotle's definition of soul and outlines his own study of it, which is then pursued as follows: DA II.4 discusses nutrition and reproduction; DA II.5–6 discuss sensation in general; DA II.7–11 discuss each of the five senses (in the following order: sight, sound, smell, taste, and touch—one chapter for each); DA II.12 again takes up the general question of sensation;
Book III DA III.1 argues there are no other senses than the five already mentioned; DA III.2 discusses the problem of what it means to "sense sensing" (i.e., to "be aware" of sensation); DA III.3 investigates the nature of imagination; DA III.4–7 discuss thinking and the intellect, or mind; DA III.8 articulates the definition and nature of soul; DA III.9–10 discuss the movement of animals possessing all the senses; DA III.11 discusses the movement of animals possessing only touch; DA III.12–13 take up the question of what are the minimal constituents of having a soul and being alive.
Summary Book I contains a summary of Aristotle's method of investigation and a dialectical determination of the nature of the soul. He begins by conceding that attempting to define the soul is one of the most difficult questions in the world. But he proposes an ingenious method to tackle the question: Just as we can come to know the properties and operations of something through scientific demonstration, i.e. a geometrical proof that a triangle has its interior angles equal to two right angles, since the principle of all scientific demonstration is the essence of the object, so too we can come to know the nature of a thing if we already know its properties and operations. It is like finding the middle term to a syllogism with a known conclusion. Therefore, we must seek out such operations of the soul to determine what kind of nature it has. From a consideration of the opinions of his predecessors, a soul, he concludes, will be that in virtue of which living things have life. Book II contains his scientific determination of the nature of the soul, an element of his biology. By dividing substance into its three meanings (matter, form, and what is composed of both), he shows that the soul must be the first actuality of a natural, organized body. This is its form or essence. It cannot be matter because the soul is that in virtue of which things have life, and matter is only being in potency. The rest of the book is divided into a determination of the nature of the nutritive and sensitive souls.
(1) All species of living things, plant or animal, must be able to nourish themselves, and reproduce others of the same kind. (2) All animals have, in addition to the nutritive power, sense-perception, and thus they all have at least the sense of touch, which he argues is presupposed by all other senses, and the ability to feel pleasure and pain, which is the simplest kind of perception. If they can feel pleasure and pain they also have desire. Some animals in addition have other senses (sight, hearing, taste), and some have more subtle versions of each (the ability to distinguish objects in a complex way, beyond mere pleasure and pain.) He discusses how these function. Some animals have in addition the powers of memory, imagination, and self-motion.
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