Summa Theologica  (excerpts)
Thomas Aquinas

Thomas Aquinas was born in 1225 in Italy. His beliefs and writings blended Christian faith and philosophy, with a strong interest in Aristotle. He was a prolific writer and teacher. Declared a Saint, his views heavily influenced the development of the Catholic Church. For more, see: http://www.ccel.org/ccel/aquinas/summa.html.

Proof of God’s Existence
To know that God exists in a general and confused way is implanted in us by nature, inasmuch as God is man's beatitude. For man naturally desires happiness, and what is naturally desired by man must be naturally known to him. This, however, is not to know absolutely that God exists; just as to know that someone is approaching is not the same as to know that Peter is approaching, even though it is Peter who is approaching; for many there are who imagine that man's perfect good.

The existence of God can be proved in five ways:

Therefore, whatever is in motion must be put in motion by another. If that by which it is put in motion be itself put in motion, then this also must needs be put in motion by another, and that by another again. But this cannot go on to infinity, because then there would be no first mover, and, consequently, no other mover; seeing that subsequent movers move only inasmuch as they are put in motion by the first mover; as the staff moves only because it is put in motion by the hand. Therefore it is necessary to arrive at a first mover, put in motion by no other; and this everyone understands to be God.

The second way is from the nature of the efficient cause. In the world of sense we find there is an order of efficient causes. There is no case known (neither is it, indeed, possible) in which a thing is found to be the efficient cause of itself; for so it would be prior to itself, which is impossible. … Therefore it is necessary to admit a first efficient cause, to which everyone gives the name of God.

Therefore, if at one time nothing was in existence, it would have been impossible for anything to have begun to exist; and thus even now nothing would be in existence---which is absurd. Therefore, not all beings are merely possible, but there must exist something the existence of which is necessary. … Therefore we cannot but postulate the existence of some being having of itself its own necessity, and not receiving it from another, but rather causing in others their necessity. This all men speak of as God.

The fourth way is taken from the gradation to be found in things. Among beings there are some more and some less good, true, noble and the like. But "more" and "less" are predicated of different things, according as they resemble in their different ways something which is the maximum, as a thing is said to be hotter according as it more nearly resembles that which is hottest; so that there is something which is truest, something best, something noblest and, consequently, something which is uttermost being; for those things that are greatest in truth are greatest in being, … Therefore there must also be something which is to all beings the cause of their being, goodness, and every other perfection; and this we call God.

The fifth way is taken from the governance of the world. We see that things which lack intelligence, such as natural bodies, act for an end, and this is evident from their acting always, or nearly always, in the same way, so as to obtain the best result. Hence it is plain that not fortuitously, but designedly, do they achieve their end. Now whatever lacks intelligence cannot move towards an end, unless it be directed by some being endowed with knowledge and intelligence; as the arrow is shot to its mark by the archer. Therefore some intelligent being exists by whom all natural things are directed to their end; and this being we call God.

Truth
Augustine says (De Vera Relig. xxxvi), "Truth is that whereby is made manifest that which is;" and Hilary says (De Trin. v) that "Truth makes being clear and evident" and this pertains to truth according as it is in the intellect. As to the truth of things in so far as they are related to the intellect, we have Augustine's definition (De Vera Relig. xxxvi), "Truth is a supreme likeness without any unlikeness to a principle": also Anselm's definition (De Verit. xii), "Truth is rightness, perceptible by the mind alone"; for that is right which is in accordance with the principle; also Avicenna's definition (Metaph. viii, 6), "The truth of each thing is a property of the essence which is immutably attached to it." The definition that "Truth is the equation of thought and thing" is applicable to it under either aspect.

For this reason truth is defined by the conformity of intellect and thing; and hence to know this conformity is to know truth. But in no way can sense know this. For although sight has the likeness of a visible thing, yet it does not know the comparison which exists between the thing seen and that which itself apprehends concerning it. But the intellect can know its own conformity with the intelligible thing; yet it does not apprehend it by knowing of a thing "what a thing is." When, however, it judges that a thing corresponds to the form which it apprehends about that thing, then first it knows and expresses truth. This it does by composing and dividing: for in every proposition it either applies to, or removes from the thing signified by the subject.

God’s Love
We must needs assert that in God there is love: because love is the first movement of the will and of every appetitive faculty. For since the acts of the will and of every appetitive faculty tend towards good and evil, as to their proper objects: and since good is essentially and especially the object of the will and the appetite, whereas evil is only the object secondarily and indirectly, as opposed to good; it follows that the acts of the will and appetite that regard good must naturally be prior to those that regard evil; thus, for instance, joy is prior to sorrow, love to hate: because what exists of itself is always prior to that which exists through another.

Since to love a thing is to will it good, in a twofold way anything may be loved more, or less. In one way on the part of the act of the will itself, which is more or less intense. In this way God does not love some things more than others, because He loves all things by an act of the will that is one, simple, and always the same.

Free Will
But man acts from judgment, because by his apprehensive power he judges that something should be avoided or sought. But because this judgment, in the case of some particular act, is not from a natural instinct, but from some act of comparison in the reason, therefore he acts from free judgment and retains the power of being inclined to various things. For reason in contingent matters may follow opposite courses, as we see in dialectic syllogisms and rhetorical arguments. Now particular operations are contingent, and therefore in such matters the judgment of reason may follow opposite courses, and is not determinate to one. And forasmuch as man is rational is it necessary that man have a free-will.

The Purpose of Man
Since, as Damascene states (De Fide Orth. ii, 12), man is said to be made in God's image, in so far as the image implies "an intelligent being endowed with free-will and self-movement": now that we have treated of the exemplar, i.e. God, and of those things which came forth from the power of God in accordance with His will; it remains for us to treat of His image, i.e. man, inasmuch as he too is the principle of his actions, as having free-will and control of his actions. … In this matter we shall consider first the last end of human life; and secondly, those things by means of which man may advance towards this end, or stray from the path: for the end is the rule of whatever is ordained to the end. And since the last end of human life is stated to be happiness, we must consider (1) the last end in general; (2) happiness.

For man and other rational creatures attain to their last end by knowing and loving God: … Hence it is evident how the objections are solved: since happiness means the acquisition of the last end.

Happiness
It is impossible for man's happiness to consist in wealth. For wealth is twofold, as the Philosopher says (Polit. i, 3), viz. natural and artificial. Natural wealth is that which serves man as a remedy for his natural wants: such as food, drink, clothing, cars, dwellings, and such like, while artificial wealth is that which is not a direct help to nature, as money, but is invented by the art of man, for the convenience of exchange, and as a measure of things salable. Now it is evident that man's happiness cannot consist in natural wealth. For wealth of this kind is sought for the sake of something else, viz. as a support of human nature: consequently it cannot be man's last end, rather is it ordained to man as to its end. Wherefore in the order of nature, all such things are below man, and made for him, according to Ps. 8:8: "Thou hast subjected all things under his feet." And as to artificial wealth, it is not sought save for the sake of natural wealth; since man would not seek it except because, by its means, he procures for himself the necessaries of life. Consequently much less can it be considered in the light of the last end. Therefore it is impossible for happiness, which is the last end of man, to consist in wealth.

[F]or it is written (Eccles. 5:12) that "riches" are sometimes "kept to the hurt of the owner"; and the same may be said of the other three. Fourthly, because man is ordained to happiness through principles that are in him; since he is ordained thereto naturally. Now the four goods mentioned above are due rather to external causes, and in most cases to fortune; for which reason they are called goods of fortune. Therefore it is evident that happiness nowise consists in the foregoing.

Consequently it is evident that good which is fitting to the body, and which causes bodily delight through being apprehended by sense, is not man's perfect good, but is quite a trifle as compared with the good of the soul. Hence it is written (Wis. 7:9) that "all gold in comparison of her, is as a little sand." And therefore bodily pleasure is neither happiness itself, nor a proper accident of happiness.

Therefore the thing itself which is desired as end, is that which constitutes happiness, and makes man happy; but the attainment of this thing is called happiness. Consequently we must say that happiness is something belonging to the soul; but that which constitutes happiness is something outside the soul.

It is impossible for any created good to constitute man's happiness. For happiness is the perfect good, which lulls the appetite altogether; else it would not be the last end, if something yet remained to be desired. Now the object of the will, i.e. of man's appetite, is the universal good; just as the object of the intellect is the universal true. Hence it is evident that naught can lull man's will, save the universal good. This is to be found, not in any creature, but in God alone; because every creature has goodness by participation. Wherefore God alone can satisfy the will of man, according to the words of Ps. 102:5: "Who satisfieth thy desire with good things." Therefore God alone constitutes man's happiness.

Final and perfect happiness can consist in nothing else than the vision of the Divine Essence. To make this clear, two points must be observed. First, that man is not perfectly happy, so long as something remains for him to desire and seek: secondly, that the perfection of any power is determined by the nature of its object. Now the object of the intellect is "what a thing is," i.e. the essence of a thing, according to De Anima iii, 6. Wherefore the intellect attains perfection, in so far as it knows the essence of a thing. … Consequently, for perfect happiness the intellect needs to reach the very Essence of the First Cause. And thus it will have its perfection through union with God as with that object, in which alone man's happiness consists,

Virtue
We come now to the consideration of habits specifically. And since habits, as we have said (Q[54], A[3]), are divided into good and bad, we must speak in the first place of good habits, which are virtues, and of other matters connected with them, namely the Gifts, Beatitudes and Fruits; in the second place, of bad habits, namely of vices and sins.

And therefore, human virtue, of which we are speaking now, cannot belong to the body, but belongs only to that which is proper to the soul. Wherefore human virtue does not imply reference to being, but rather to act. Consequently it is essential to human virtue to be an operative habit.

It cannot be said that there is only one moral virtue about all the passions: since some passions are not in the same power as other passions; … First, because some passions are in contrary opposition to one another, such as joy and sorrow, fear and daring, and so on. About such passions as are thus in opposition to one another there must needs be one same virtue. Because, since moral virtue consists in a kind of mean, the mean in contrary passions stands in the same ratio to both, even as in the natural order there is but one mean between contraries, e.g. between black and white. … On the other hand, the irascible passions are not all of one order, but are directed to different things: for daring and fear are about some great danger; hope and despair are about some difficult good; while anger seeks to overcome something contrary which has wrought harm. Consequently there are different virtues about such like passions: e.g. temperance, about the concupiscible passions; fortitude, about fear and daring; magnanimity, about hope and despair; meekness, about anger.

Things may be numbered either in respect of their formal principles, or according to the subjects in which they are: and either way we find that there are four cardinal virtues. For the formal principle of the virtue of which we speak now is good as defined by reason; which good is considered in two ways. First, as existing in the very act of reason: and thus we have one principal virtue, called "Prudence." Secondly, according as the reason puts its order into something else; either into operations, and then we have "Justice"; or into passions, and then we need two virtues. For the need of putting the order of reason into the passions is due to their thwarting reason: and this occurs in two ways. First, by the passions inciting to something against reason, and then the passions need a curb, which we call "Temperance." Secondly, by the passions withdrawing us from following the dictate of reason, e.g. through fear of danger or toil: and then man needs to be strengthened for that which reason dictates, lest he turn back; and to this end there is "Fortitude."

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