[Meaning something that is] efficient; formal; final. Aristotle says that the soul is like a principle of animals, inasmuch as [it is] efficient, formal, and final; for these are the principles in the strict sense. Now [sc. a principle can be understood] as "efficient" because the soul sets in motion the animal with its wish alone, and requires no leverage; [sc. and it can be understood] as "formal" because the soul itself endows with form the animal and animate things altogether. For the animate forms are said to be this very thing [sc. animate][1] because they have soul. In fact, the more excellent component in each natural thing is its form; and the soul is the more excellent component in the animate things. And [sc. a principle can be understood] as "final" because the body is for the sake of the soul, for the body exists for the sake of something and the soul is that for the sake of which [something exists].[2] Hence the structural organization of animals is also, in one way or another, in view of the peculiar character of the soul in each thing. However the soul of animals is a principle which is rather distant, while nature is a proximate [principle]. But of things necessarily following the soul, some accompany it and others accompany the animal as a whole (I mean, that is, the compound of life[3] and body). And some things are affections of the soul, such as intellection (for this is something peculiar to the soul), but other affections (such as "to perceive", "to have images or presentations", "to be wroth", "to have appetites" and anything else of that sort) are common to both of these components. He used to say that the five genera (substance, sameness, otherness, motion, rest) are the principles of all existing things. And he said that these genera are not like those of the Peripatetic philosophers (such genera being distinguished by each other, and some trace of the subordinate genera and forms extends from each), but as pervading genera going through all the existing things. For the substance according to which the being of each thing is (what it is) is in all the things. And sameness is that in virtue of which we are (what we are) from a single principle of the existing things. And we also have otherness, since the existing things are a multiplicity as well; and where there is multiplicity, there is otherness. And within the domain of all the existing things there is motion as well. I mean "motion", not "incomplete activity", but the effective or actual motion of each thing. For all the things contain a proper activity, even the inanimate things themselves. In fact, such things produce heat or cold to what is associated with them, or make them moist or dry, or produce some other effect of this sort. And the rest is considered in all the cases, for the things which are in perpetual motion also partake of rest, and rest is not only to be present with regard to the wholeness but also to remain itself in the perpetual motion. Therefore, the things in motion remain either always or during a certain time and, in accordance with this itself, they partake of rest.