I answer that, Every agent, of necessity, acts for an end. For if, in a number of causes ordained to one another, the first be removed, the others must, of necessity, be removed also. Now the first of all causes is the final cause. The reason of which is that matter does not receive form, save in so far as it is moved by an agent; for nothing reduces itself from potentiality to act. But an agent does not move except out of intention for an end. For if the agent were not determinate to some particular effect, it would not do one thing rather than another: consequently in order that it produce a determinate effect, it must, of necessity, be determined to some certain one, which has the nature of an end. And just as this determination is effected, in the rational nature, by the "rational appetite," which is called the will; so, in other things, it is caused by their natural inclination, which is called the "natural appetite."
Nevertheless it must be observed that a thing tends to an end, by its action or movement, in two ways: first, as a thing, moving itself to the end, as man; secondly, as a thing moved by another to the end, as an arrow tends to a determinate end through being moved by the archer who directs his action to the end. Therefore those things that are possessed of reason, move themselves to an end; because they have dominion over their actions through their free-will, which is the "faculty of will and reason." But those things that lack reason tend to an end, by natural inclination, as being moved by another and not by themselves; since they do not know the nature of an end as such, and consequently cannot ordain anything to an end, but can be ordained to an end only by another. For the entire irrational nature is in comparison to God as an instrument to the principal agent, as stated above (FP, Q[22], A[2], ad 4; FP, Q[103], A[1], ad 3). Consequently it is proper to the rational nature to tend to an end, as directing [agens] and leading itself to the end: whereas it is proper to the irrational nature to tend to an end, as directed or led by another, whether it apprehend the end, as do irrational animals, or do not apprehend it, as is the case of those things which are altogether void of knowledge.
Reply to Objection 1: When a man of himself acts for an end, he knows the end: but when he is directed or led by another, for instance, when he acts at another's command, or when he is moved under another's compulsion, it is not necessary that he should know the end. And it is thus with irrational creatures.
Reply to Objection 2: To ordain towards an end belongs to that which directs itself to an end: whereas to be ordained to an end belongs to that which is directed by another to an end. And this can belong to an irrational nature, but owing to some one possessed of reason.
Reply to Objection 3: The object of the will is the end and the good in universal. Consequently there can be no will in those things that lack reason and intellect, since they cannot apprehend the universal; but they have a natural appetite or a sensitive appetite, determinate to some particular good. Now it is clear that particular causes are moved by a universal cause: thus the governor of a city, who intends the common good, moves, by his command, all the particular departments of the city. Consequently all things that lack reason are, of necessity, moved to their particular ends by some rational will which extends to the universal good, namely by the Divine will.
Whether human acts are specified by their end?
Objection 1: It would seem that human acts are not specified by their end. For the end is an extrinsic cause. But everything is specified by an intrinsic principle. Therefore human acts are not specified by their end.
Objection 2: Further, that which gives a thing its species should exist before it. But the end comes into existence afterwards. Therefore a human act does not derive its species from the end.
Objection 3: Further, one thing cannot be in more than one species. But one and the same act may happen to be ordained to various ends. Therefore the end does not give the species to human acts.
On the contrary, Augustine says (De Mor. Eccl. et Manich. ii, 13): "According as their end is worthy of blame or praise so are our deeds worthy of blame or praise."
I answer that Each thing receives its species in respect of an act and not in respect of potentiality; wherefore things composed of matter and form are established in their respective species by their own forms. And this is also to be observed in proper movements. For since movements are, in a way, divided into action and passion, each of these receives its species from an act; action indeed from the act which is the principle of acting, and passion from the act which is the terminus of the movement. Wherefore heating, as an action, is nothing else than a certain movement proceeding from heat, while heating as a passion is nothing else than a movement towards heat: and it is the definition that shows the specific nature. And either way, human acts, whether they be considered as actions, or as passions, receive their species from the end. For human acts can be considered in both ways, since man moves himself, and is moved by himself. Now it has been stated above (A[1]) that acts are called human, inasmuch as they proceed from a deliberate will. Now the object of the will is the good and the end. And hence it is clear that the principle of human acts, in so far as they are human, is the end. In like manner it is their terminus: for the human act terminates at that which the will intends as the end; thus in natural agents the form of the thing generated is conformed to the form of the generator. And since, as Ambrose says (Prolog. super Luc.) "morality is said properly of man," moral acts properly speaking receive their species from the end, for moral acts are the same as human acts.
Reply to Objection 1: The end is not altogether extrinsic to the act, because it is related to the act as principle or terminus; and thus it just this that is essential to an act, viz. to proceed from something, considered as action, and to proceed towards something, considered as passion.
Reply to Objection 2: The end, in so far as it pre-exists in the intention, pertains to the will, as stated above (A[1], ad 1). And it is thus that it gives the species to the human or moral act.
Reply to Objection 3: One and the same act, in so far as it proceeds once from the agent, is ordained to but one proximate end, from which it has its species: but it can be ordained to several remote ends, of which one is the end of the other. It is possible, however, that an act which is one in respect of its natural species, be ordained to several ends of the will: thus this act "to kill a man," which is but one act in respect of its natural species, can be ordained, as to an end, to the safeguarding of justice, and to the satisfying of anger: the result being that there would be several acts in different species of morality: since in one way there will be an act of virtue, in another, an act of vice. For a movement does not receive its species from that which is its terminus accidentally, but only from that which is its "per se" terminus. Now moral ends are accidental to a natural thing, and conversely the relation to a natural end is accidental to morality. Consequently there is no reason why acts which are the same considered in their natural species, should not be diverse, considered in their moral species, and conversely.
Whether there is one last end of human life?
Objection 1: It would seem that there is no last end of human life, but that we proceed to infinity. For good is essentially diffusive, as Dionysius states (Div. Nom. iv). Consequently if that which proceeds from good is itself good, the latter must needs diffuse some other good: so that the diffusion of good goes on indefinitely. But good has the nature of an end. Therefore there is an indefinite series of ends.
Objection 2: Further, things pertaining to the reason can be multiplied to infinity: thus mathematical quantities have no limit. For the same reason the species of numbers are infinite, since, given any number, the reason can think of one yet greater. But desire of the end is consequent on the apprehension of the reason. Therefore it seems that there is also an infinite series of ends.
Objection 3: Further, the good and the end is the object of the will. But the will can react on itself an infinite number of times: for I can will something, and will to will it, and so on indefinitely. Therefore there is an infinite series of ends of the human will, and there is no last end of the human will.
On the contrary, The Philosopher says (Metaph. ii, 2) that "to suppose a thing to be indefinite is to deny that it is good." But the good is that which has the nature of an end. Therefore it is contrary to the nature of an end to proceed indefinitely. Therefore it is necessary to fix one last end.
I answer that, Absolutely speaking, it is not possible to proceed indefinitely in the matter of ends, from any point of view. For in whatsoever things there is an essential order of one to another, if the first be removed, those that are ordained to the first, must of necessity be removed also. Wherefore the Philosopher proves (Phys. viii, 5) that we cannot proceed to infinitude in causes of movement, because then there would be no first mover, without which neither can the others move, since they move only through being moved by the first mover. Now there is to be observed a twofold order in ends---the order of intention and the order of execution: and in either of these orders there must be something first. For that which is first in the order of intention, is the principle, as it were, moving the appetite; consequently, if you remove this principle, there will be nothing to move the appetite. On the other hand, the principle in execution is that wherein operation has its beginning; and if this principle be taken away, no one will begin to work. Now the principle in the intention is the last end; while the principle in execution is the first of the things which are ordained to the end. Consequently, on neither side is it possible to go to infinity since if there were no last end, nothing would be desired, nor would any action have its term, nor would the intention of the agent be at rest; while if there is no first thing among those that are ordained to the end, none would begin to work at anything, and counsel would have no term, but would continue indefinitely.
On the other hand, nothing hinders infinity from being in things that are ordained to one another not essentially but accidentally; for accidental causes are indeterminate. And in this way it happens that there is an accidental infinity of ends, and of things ordained to the end.
Reply to Objection 1: The very nature of good is that something flows from it, but not that it flows from something else. Since, therefore, good has the nature of end, and the first good is the last end, this argument does not prove that there is no last end; but that from the end, already supposed, we may proceed downwards indefinitely towards those things that are ordained to the end. And this would be true if we considered but the power of the First Good, which is infinite. But, since the First Good diffuses itself according to the intellect, to which it is proper to flow forth into its effects according to a certain fixed form; it follows that there is a certain measure to the flow of good things from the First Good from Which all other goods share the power of diffusion. Consequently the diffusion of goods does not proceed indefinitely but, as it is written ( Wis. 11:21 ), God disposes all things "in number, weight and measure."
Reply to Objection 2: In things which are of themselves, reason begins from principles that are known naturally, and advances to some term. Wherefore the Philosopher proves (Poster. i, 3) that there is no infinite process in demonstrations, because there we find a process of things having an essential, not an accidental, connection with one another. But in those things which are accidentally connected, nothing hinders the reason from proceeding indefinitely. Now it is accidental to a stated quantity or number, as such, that quantity or unity be added to it. Wherefore in such like things nothing hinders the reason from an indefinite process.
Reply to Objection 3: This multiplication of acts of the will reacting on itself, is accidental to the order of ends. This is clear from the fact that in regard to one and the same end, the will reacts on itself indifferently once or several times.
Whether one man can have several last ends?