On the Soul (Greek Περὶ Ψυχῆς (Perì Psūchês), Latin De Anima) is a major treatise by Aristotle, outlining his philosophical views on the nature of living things. His discussion centres on the kinds of souls possessed by different kinds of living things, distinguished by the different life-processes those organisms go through. Thus 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.
The notion of soul used by Aristotle is only distantly related to the usual modern conception. He holds that the soul is the form, or essence of any living thing; that it is not a distinct substance from the body that it is in; that it is the possession of soul (of a specific kind) that makes an organism an organism at all, and thus that the notion of a body without a soul, or of a soul in the wrong kind of body, is simply unintelligible. (He speculates that some parts of the soul--the intellect--may be conceived to exist without the body, but most cannot.) It is difficult to reconcile these points with the popular picture of a soul as a sort of spiritual substance "inhabiting" a body. Some commentators have suggested that Aristotle's term soul is better translated as lifeforce.
Averroes (Ibn Rushd) (1126-1198) was an Andalusian-Arab philosopher and physician. He wrote commentaries on most of the surviving works of Aristotle. These were not based on primary sources (it is not known whether he knew Greek), but rather on Arabic translations. On each work, he wrote the Jami, the Talkhis and the Tafsir which are, respectively, a simplified overview, an intermediate commentary with more critical material, and an advanced study of Aristotelian thought in a Muslim context. The terms are taken from the names of different types of commentary on the Qur'an.