and that which is first in a class is always best or analogous to the best.That the final cause may apply to immovable things is shown by the distinction of its meanings. For the final cause is not only "the good for something," but also "the good which is the end of some action." In the latter sense it applies to immovable things, although in the former it does not; and it causes motion as being an object of love, whereas all other things cause motion because they are themselves in motion.Now if a thing is moved, it can be otherwise than it is. Therefore if the actuality of "the heaven" is primary locomotion, then in so far as "the heaven" is moved, in this respect at least it is possible for it to be otherwise; i.e. in respect of place, even if not of substantiality. But since there is something—X—which moves while being itself unmoved, existing actually, X cannot be otherwise in any respect.For the primary kind of change is locomotion,Proved in Aristot. Physics 8.7. and of locomotion circular locomotion Aristot. Physics 8.9 ; and this is the motion which X induces. Thus X is necessarily existent; and qua necessary it is good, and is in this sense a first principle.The argument is: X (the prime mover), since it imparts the primary motion, cannot be liable to motion (or change) of any kind. Therefore it exists of necessity, and must be good (cf. Aristot. Met. 5.5.6); and it is qua good, i.e., the object of desire, that X is a first principle. For the necessary has all these meanings: that which is by constraint because it is contrary to impulse; and that without which excellence is impossible; and that which cannot be otherwise, but is absolutely necessary.Cf. Aristot. Met. 5.5Such, then, is the first principle upon which depend the sensible universe and the world of nature.And its life is like the best which we temporarily enjoy. It must be in that state always (which for us is impossible), since its actuality is also pleasure.For the relation of pleasure to actuality or activity see Aristot. Nic. Eth. 10.4.(And for this reason waking, sensation and thinking are most pleasant, and hopes and memories are pleasant because of them.) Now thinking in itself is concerned with that which is in itself best, and thinking in the highest sense with that which is in the highest sense best.Since the prime mover is pure actuality, and has or rather is the highest form of life, Aristotle identifies it with the highest activity—pure thinking.And thought thinks itself through participation in the object of thought; for it becomes an object of thought by the act of apprehension and thinking, so that thought and the object of thought are the same, because that which is receptive of the object of thought, i.e. essence, is thought. And it actually functions when it possesses this object.In actualization the subject and object of thought (like those of perception, Aristot. De Anima 3.2.) are identical. Hence it is actuality rather than potentiality that is held to be the divine possession of rational thought, and its active contemplation is that which is most pleasant and best.If, then, the happiness which God always enjoys is as great as that which we enjoy sometimes, it is marvellous; and if it is greater, this is still more marvellous. Nevertheless it is so. Moreover, life belongs to God. For the actuality of thought is life, and God is that actuality; and the essential actuality of God is life most good and eternal. We hold, then, that God is a living being, eternal, most good; and therefore life and a continuous eternal existence belong to God; for that is what God is. Those who suppose, as do the Pythagoreans and Speusippus,The view is referred to again in Aristot. Met. 12.10.6, Aristot. Met. 14.4.2, 3, Aristot. Met. 14.5.1. that perfect beauty and goodness donot exist in the beginning (on the ground that whereas the first beginnings of plants and animals are causes, it is in the products of these that beauty and perfection are found) are mistaken in their views.For seed comes from prior creatures which are perfect, and that which is first is not the seed but the perfect creature.