Article [3]), our intellect, which takes cognizance of the essence of a thing as its proper object, gains knowledge from sense, of which the proper objects are external accidents. Hence from external appearances we come to the knowledge of the essence of things. And because we name a thing in accordance with our knowledge of it, as is clear from what has already been said ( Question [13], Article [1]), so from external properties names are often imposed to signify essences. Hence such names are sometimes taken strictly to denote the essence itself, the signification of which is their principal object; but sometimes, and less strictly, to denote the properties by reason of which they are imposed. And so we see that the word "body" is used to denote a genus of substances from the fact of their possessing three dimensions: and is sometimes taken to denote the dimensions themselves; in which sense body is said to be a species of quantity. The same must be said of life. The name is given from a certain external appearance, namely, self-movement, yet not precisely to signify this, but rather a substance to which self-movement and the application of itself to any kind of operation, belong naturally. To live, accordingly, is nothing else than to exist in this or that nature; and life signifies this, though in the abstract, just as the word "running" denotes "to run" in the abstract.
Hence "living" is not an accidental but an essential predicate. Sometimes, however, life is used less properly for the operations from which its name is taken, and thus the Philosopher says (Ethic. ix, 9) that to live is principally to sense or to understand.
Reply to Objection 1: The Philosopher here takes "to live" to mean an operation of life. Or it would be better to say that sensation and intelligence and the like, are sometimes taken for the operations, sometimes for the existence itself of the operator. For he says (Ethic. ix, 9) that to live is to sense or to understand---in other words, to have a nature capable of sensation or understanding. Thus, then, he distinguishes life by the four operations mentioned. For in this lower world there are four kinds of living things. It is the nature of some to be capable of nothing more than taking nourishment, and, as a consequence, of growing and generating. Others are able, in addition, to sense, as we see in the case of shellfish and other animals without movement. Others have the further power of moving from place to place, as perfect animals, such as quadrupeds, and birds, and so on. Others, as man, have the still higher faculty of understanding.
Reply to Objection 2: By vital operations are meant those whose principles are within the operator, and in virtue of which the operator produces such operations of itself. It happens that there exist in men not merely such natural principles of certain operations as are their natural powers, but something over and above these, such as habits inclining them like a second nature to particular kinds of operations, so that the operations become sources of pleasure. Thus, as by a similitude, any kind of work in which a man takes delight, so that his bent is towards it, his time spent in it, and his whole life ordered with a view to it, is said to be the life of that man. Hence some are said to lead to life of self-indulgence, others a life of virtue. In this way the contemplative life is distinguished from the active, and thus to know God is said to be life eternal.
Wherefore the Reply to the Third Objection is clear.
Whether life is properly attributed to God?
Objection 1: It seems that life is not properly attributed to God. For things are said to live inasmuch as they move themselves, as previously stated ( Article [2]). But movement does not belong to God. Neither therefore does life.
Objection 2: Further, in all living things we must needs suppose some principle of life. Hence it is said by the Philosopher (De Anima ii, 4) that "the soul is the cause and principle of the living body." But God has no principle. Therefore life cannot be attributed to Him.
Objection 3: Further, the principle of life in the living things that exist among us is the vegetative soul. But this exists only in corporeal things. Therefore life cannot be attributed to incorporeal things.
On the contrary, It is said (Ps. 83:3): "My heart and my flesh have rejoiced in the living God."
I answer that, Life is in the highest degree properly in God. In proof of which it must be considered that since a thing is said to live in so far as it operates of itself and not as moved by another, the more perfectly this power is found in anything, the more perfect is the life of that thing. In things that move and are moved, a threefold order is found. In the first place, the end moves the agent: and the principal agent is that which acts through its form, and sometimes it does so through some instrument that acts by virtue not of its own form, but of the principal agent, and does no more than execute the action. Accordingly there are things that move themselves, not in respect of any form or end naturally inherent in them, but only in respect of the executing of the movement; the form by which they act, and the end of the action being alike determined for them by their nature. Of this kind are plants, which move themselves according to their inherent nature, with regard only to executing the movements of growth and decay.
Other things have self-movement in a higher degree, that is, not only with regard to executing the movement, but even as regards to the form, the principle of movement, which form they acquire of themselves. Of this kind are animals, in which the principle of movement is not a naturally implanted form; but one received through sense. Hence the more perfect is their sense, the more perfect is their power of self-movement. Such as have only the sense of touch, as shellfish, move only with the motion of expansion and contraction; and thus their movement hardly exceeds that of plants. Whereas such as have the sensitive power in perfection, so as to recognize not only connection and touch, but also objects apart from themselves, can move themselves to a distance by progressive movement. Yet although animals of the latter kind receive through sense the form that is the principle of their movement, nevertheless they cannot of themselves propose to themselves the end of their operation, or movement; for this has been implanted in them by nature; and by natural instinct they are moved to any action through the form apprehended by sense. Hence such animals as move themselves in respect to an end they themselves propose are superior to these. This can only be done by reason and intellect; whose province it is to know the proportion between the end and the means to that end, and duly coordinate them. Hence a more perfect degree of life is that of intelligible beings; for their power of self-movement is more perfect. This is shown by the fact that in one and the same man the intellectual faculty moves the sensitive powers; and these by their command move the organs of movement. Thus in the arts we see that the art of using a ship, i.e. the art of navigation, rules the art of ship-designing; and this in its turn rules the art that is only concerned with preparing the material for the ship.
But although our intellect moves itself to some things, yet others are supplied by nature, as are first principles, which it cannot doubt; and the last end, which it cannot but will. Hence, although with respect to some things it moves itself, yet with regard to other things it must be moved by another. Wherefore that being whose act of understanding is its very nature, and which, in what it naturally possesses, is not determined by another, must have life in the most perfect degree. Such is God; and hence in Him principally is life. From this the Philosopher concludes (Metaph. xii, 51), after showing God to be intelligent, that God has life most perfect and eternal, since His intellect is most perfect and always in act.
Reply to Objection 1: As stated in Metaph. ix, 16, action is twofold. Actions of one kind pass out to external matter, as to heat or to cut; whilst actions of the other kind remain in the agent, as to understand, to sense and to will. The difference between them is this, that the former action is the perfection not of the agent that moves, but of the thing moved; whereas the latter action is the
