Thomas Aquinas

“ 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. ”

“ Waters are called living that have a continuous current: for standing waters, that are not connected with a continually flowing source, are called dead, as in cisterns and ponds. This is merely a similitude, inasmuch as the movement they are seen to possess makes them look as if they were alive. Yet this is not life in them in its real sense, since this movement of theirs is not from themselves but from the cause that generates them. The same is the case with the movement of other heavy and light bodies. ”

“ 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. ”

“ Whereby it is clear that those things are properly called living that move themselves by some kind of movement, whether it be movement properly so called, as the act of an imperfect being, i.e. of a thing in potentiality, is called movement; or movement in a more general sense, as when said of the act of a perfect thing, as understanding and feeling are called movement. Accordingly all things are said to be alive that determine themselves to movement or operation of any kind: whereas those things that cannot by their nature do so, cannot be called living, unless by a similitude. ”

“ 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. ”

“ 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 ”

“ Although bad things are in God's knowledge, as being comprised under that knowledge, yet they are not in God as created by Him, or preserved by Him, or as having their type in Him. They are known by God through the types of good things. Hence it cannot be said that bad things are life in God. Those things that are not in time may be called life in God in so far as life means understanding only, and inasmuch as they are understood by God; but not in so far as life implies a principle of operation. ”

“ Art. 2 - Whether life is an operation? Objection 1: It seems that life is an operation. For nothing is divided except into parts of the same genus. But life is divided by certain operations, as is clear from the Philosopher (De Anima ii, 13) , who distinguishes four kinds of life, namely, nourishment, sensation, local movement and understanding. Therefore life is an operation. ”

“ But since matter enters into the being of natural things, we must say that those things have simply being in the divine mind more truly than in themselves, because in that mind they have an uncreated being, but in themselves a created being: whereas this particular being, a man, or horse, for example, has this being more truly in its own nature than in the divine mind, because it belongs to human nature to be material, which, as existing in the divine mind, it is not. Even so a house has nobler being in the architect's mind than in matter ”

“ 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 ”

“ 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. ”

“ In either way is movement called the life, as it were, of natural bodies, speaking by a similitude, and not attributing it to them as their property. The movement of the heavens is in the universe of corporeal natures as the movement of the heart, whereby life is preserved, is in animals. Similarly also every natural movement in respect to natural things has a certain similitude to the operations of life. ”

“ For sometimes the form has being of another kind in the model from that which it has in the thing modelled. Thus the form of a house has in the mind of the architect immaterial and intelligible being; but in the house that exists outside his mind, material and sensible being. ”

“ 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. ”

“ 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 ”

“ Hence, because movement is an act of the thing in movement, the latter action, in so far as it is the act of the operator, is called its movement, by this similitude, that as movement is an act of the thing moved, so an act of this kind is the act of the agent, although movement is an act of the imperfect, that is, of what is in potentiality ”

“ I answer that, We can gather to what things life belongs, and to what it does not, from such things as manifestly possess life. Now life manifestly belongs to animals, for it said in De Vegetab. i [*De Plantis i, 1] that in animals life is manifest. ”