Summa Theologica, by St. Thomas Aquinas, , at sacred-texts.com
We must now consider the causes of sin: (1) in general; (2) in particular. Under the first head there are four points of inquiry:
(1) Whether sin has a cause?
(2) Whether it has an internal cause?
(3) Whether it has an external cause?
(4) Whether one sin is the cause of another?
Objection 1: It would seem that sin has no cause. For sin has the nature of evil, as stated above (Q, A). But evil has no cause, as Dionysius says (Div. Nom. iv). Therefore sin has no cause.
Objection 2: Further, a cause is that from which something follows of necessity. Now that which is of necessity, seems to be no sin, for every sin is voluntary. Therefore sin has no cause.
Objection 3: Further, if sin has a cause, this cause is either good or evil. It is not a good, because good produces nothing but good, for "a good tree cannot bring forth evil fruit" (Mat. 7:18). Likewise neither can evil be the cause of sin, because the evil of punishment is a sequel to sin, and the evil of guilt is the same as sin. Therefore sin has no cause.
On the contrary, Whatever is done has a cause, for, according to Job 5:6, "nothing upon earth is done without a cause." But sin is something done; since it a "word, deed, or desire contrary to the law of God." Therefore sin has a cause.
I answer that, A sin is an inordinate act. Accordingly, so far as it is an act, it can have a direct cause, even as any other act; but, so far as it is inordinate, it has a cause, in the same way as a negation or privation can have a cause. Now two causes may be assigned to a negation: in the first place, absence of the cause of affirmation; i.e. the negation of the cause itself, is the cause of the negation in itself; since the result of the removing the cause is the removal of the effect: thus the absence of the sun is the cause of darkness. In the second place, the cause of an affirmation, of which a negation is a sequel, is the accidental cause of the resulting negation: thus fire by causing heat in virtue of its principal tendency, consequently causes a privation of cold. The first of these suffices to cause a simple negation. But, since the inordinateness of sin and of every evil is not a simple negation, but the privation of that which something ought naturally to have, such an inordinateness must needs have an accidental efficient cause. For that which naturally is and ought to be in a thing, is never lacking except on account of some impeding cause. And accordingly we are wont to say that evil, which consists in a certain privation, has a deficient cause, or an accidental efficient cause. Now every accidental cause is reducible to the direct cause. Since then sin, on the part of its inordinateness, has an accidental efficient cause, and on the part of the act, a direct efficient cause, it follows that the inordinateness of sin is a result of the cause of the act. Accordingly then, the will lacking the direction of the rule of reason and of the Divine law, and intent on some mutable good, causes the act of sin directly, and the inordinateness of the act, indirectly, and beside the intention: for the lack of order in the act results from the lack of direction in the will.
Reply to Objection 1: Sin signifies not only the privation of good, which privation is its inordinateness, but also the act which is the subject of that privation, which has the nature of evil: and how this evil has a cause, has been explained.
Reply to Objection 2: If this definition is to be verified in all cases, it must be understood as applying to a cause which is sufficient and not impeded. For it happens that a thing is the sufficient cause of something else, and that the effect does not follow of necessity, on account of some supervening impediment: else it would follow that all things happen of necessity, as is proved in Metaph. vi, text. 5. Accordingly, though sin has a cause, it does not follow that this is a necessary cause, since its effect can be impeded.
Reply to Objection 3: As stated above, the will in failing to apply the rule of reason or of the Divine law, is the cause of sin. Now the fact of not applying the rule of reason or of the Divine law, has not in itself the nature of evil, whether of punishment or of guilt, before it is applied to the act. Wherefore accordingly, evil is not the cause of the first sin, but some good lacking some other good.
Objection 1: It would seem that sin has no internal cause. For that which is within a thing is always in it. If therefore sin had an internal cause, man would always be sinning, since given the cause, the effect follows.
Objection 2: Further, a thing is not its own cause. But the internal movements of a man are sins. Therefore they are not the cause of sin.
Objection 3: Further, whatever is within man is either natural or voluntary. Now that which is natural cannot be the cause of sin, for sin is contrary to nature, as Damascene states (De Fide Orth. ii, 3; iv, 21); while that which is voluntary, if it be inordinate, is already a sin. Therefore nothing intrinsic can be the cause of the first sin.
On the contrary, Augustine says (De Duabus Anim. x, 10,11; Retract. i, 9) that "the will is the cause of sin."
I answer that, As stated above (A), the direct cause of sin must be considered on the part of the act. Now we may distinguish a twofold internal cause of human acts, one remote, the other proximate. The proximate internal cause of the human act is the reason and will, in respect of which man has a free-will; while the remote cause is the apprehension of the sensitive part, and also the sensitive appetite. For just as it is due to the judgment of reason, that the will is moved to something in accord with reason, so it is due to an apprehension of the senses that the sensitive appetite is inclined to something; which inclination sometimes influences the will and reason, as we shall explain further on (Q, A). Accordingly a double interior cause of sin may be assigned; one proximate, on the part of the reason and will; and the other remote, on the part of the imagination or sensitive appetite.
But since we have said above (A, ad 3) that the cause of sin is some apparent good as motive, yet lacking the due motive, viz. the rule of reason or the Divine law, this motive which is an apparent good, appertains to the apprehension of the senses and to the appetite; while the lack of the due rule appertains to the reason, whose nature it is to consider this rule; and the completeness of the voluntary sinful act appertains to the will, so that the act of the will, given the conditions we have just mentioned, is already a sin.
Reply to Objection 1: That which is within a thing as its natural power, is always in it: but that which is within it, as the internal act of the appetitive or apprehensive power, is not always in it. Now the power of the will is the potential cause of sin, but is made actual by the preceding movements, both of the sensitive part, in the first place, and afterwards, of the reason. For it is because a thing is proposed as appetible to the senses, and because the appetite is inclined, that the reason sometimes fails to consider the due rule, so that the will produces the act of sin. Since therefore the movements that precede it are not always actual, neither is man always actually sinning.
Reply to Objection 2: It is not true that all the internal acts belong to the substance of sin, for this consists principally in the act of the will; but some precede and some follow the sin itself.
Reply to Objection 3: That which causes sin, as a power produces its act, is natural; and again, the movement of the sensitive part, from which sin follows, is natural sometimes, as, for instance, when anyone sins through appetite for food. Yet sin results in being unnatural from the very fact that the natural rule fails, which man, in accord with his nature, ought to observe.
Objection 1: It would seem that sin has no external cause. For sin is a voluntary act. Now voluntary acts belong to principles that are within us, so that they have no external cause. Therefore sin has no external cause.
Objection 2: Further, as nature is an internal principle, so is the will. Now in natural things sin can be due to no other than an internal cause; for instance, the birth of a monster is due to the corruption of some internal principle. Therefore in the moral order, sin can arise from no other than an internal cause. Therefore it has no external cause.
Objection 3: Further, if the cause is multiplied, the effect is multiplied. Now the more numerous and weighty the external inducements to sin are, the less is a man's inordinate act imputed to him as a sin. Therefore nothing external is a cause of sin.
On the contrary, It is written (Num. 21:16): "Are not these they, that deceived the children of Israel by the counsel of Balaam, and made you transgress against the Lord by the sin of Phogor?" Therefore something external can be a cause of sin.
I answer that, As stated above (A), the internal cause of sin is both the will, as completing the sinful act, and the reason, as lacking the due rule, and the appetite, as inclining to sin. Accordingly something external might be a cause of sin in three ways, either by moving the will itself immediately, or by moving the reason, or by moving the sensitive appetite. Now, as stated above (Q, A; Q, A), none can move the will inwardly save God alone, who cannot be a cause of sin, as we shall prove further on (Q, A). Hence it follows that nothing external can be a cause of sin, except by moving the reason, as a man or devil by enticing to sin; or by moving the sensitive appetite, as certain external sensibles move it. Yet neither does external enticement move the reason, of necessity, in matters of action, nor do things proposed externally, of necessity move the sensitive appetite, except perhaps it be disposed thereto in a certain way; and even the sensitive appetite does not, of necessity, move the reason and will. Therefore something external can be a cause moving to sin, but not so as to be a sufficient cause thereof: and the will alone is the sufficient completive cause of sin being accomplished.
Reply to Objection 1: From the very fact that the external motive causes of sin do not lead to sin sufficiently and necessarily, it follows that it remains in our power to sin or not to sin.
Reply to Objection 2: The fact that sin has an internal cause does not prevent its having an external cause; for nothing external is a cause of sin, except through the medium of the internal cause, as stated.
Reply to Objection 3: If the external causes inclining to sin be multiplied, the sinful acts are multiplied, because they incline to the sinful act in both greater numbers and greater frequency. Nevertheless the character of guilt is lessened, since this depends on the act being voluntary and in our power.
Objection 1: It would seem that one sin cannot be the cause of another. For there are four kinds of cause, none of which will fit in with one sin causing another. Because the end has the character of good; which is inconsistent with sin, which has the character of evil. In like manner neither can a sin be an efficient cause, since "evil is not an efficient cause, but is weak and powerless," as Dionysius declares (Div. Nom. iv). The material and formal cause seems to have no place except in natural bodies, which are composed of matter and form. Therefore sin cannot have either a material or a formal cause.
Objection 2: Further, "to produce its like belongs to a perfect thing," as stated in Meteor. iv, 2 [*Cf. De Anima ii.]. But sin is essentially something imperfect. Therefore one sin cannot be a cause of another.
Objection 3: Further, if one sin is the cause of a second sin, in the same way, yet another sin will be the cause of the first, and thus we go on indefinitely, which is absurd. Therefore one sin is not the cause of another.
On the contrary, Gregory says on Ezechiel (Hom. xi): "A sin is not quickly blotted out by repentance, is both a sin and a cause of sin."
I answer that, Forasmuch as a sin has a cause on the part of the act of sin, it is possible for one sin to be the cause of another, in the same way as one human act is the cause of another. Hence it happens that one sin may be the cause of another in respect of the four kinds of causes. First, after the manner of an efficient or moving cause, both directly and indirectly. Indirectly, as that which removes an impediment is called an indirect cause of movement: for when man, by one sinful act, loses grace, or charity, or shame, or anything else that withdraws him from sin, he thereby falls into another sin, so that the first sin is the accidental cause of the second. Directly, as when, by one sinful act, man is disposed to commit more readily another like act: because acts cause dispositions and habits inclining to like acts. Secondly, after the manner of a material cause, one sin is the cause of another, by preparing its matter: thus covetousness prepares the matter for strife, which is often about the wealth a man has amassed together. Thirdly, after the manner of a final cause, one sin causes another, in so far as a man commits one sin for the sake of another which is his end; as when a man is guilty of simony for the end of ambition, or fornication for the purpose of theft. And since the end gives the form to moral matters, as stated above (Q, A; Q, AA,6), it follows that one sin is also the formal cause of another: because in the act of fornication committed for the purpose of theft, the former is material while the latter is formal.
Reply to Objection 1: Sin, in so far as it is inordinate, has the character of evil; but, in so far as it is an act, it has some good, at least apparent, for its end: so that, as an act, but not as being inordinate, it can be the cause, both final and efficient, of another sin. A sin has matter, not "of which" but "about which" it is: and it has its form from its end. Consequently one sin can be the cause of another, in respect of the four kinds of cause, as stated above.
Reply to Objection 2: Sin is something imperfect on account of its moral imperfection on the part of its inordinateness. Nevertheless, as an act it can have natural perfection: and thus it can be the cause of another sin.
Reply to Objection 3: Not every cause of one sin is another sin; so there is no need to go on indefinitely: for one may come to one sin which is not caused by another sin.