---
title: "Summa Theologica, First Half"
author: "Thomas Aquinas"
translator: "Fathers of the English Dominican Province"
languages: [en]
shelf: "Medieval"
section: 663 of 1210
url: https://scriptura.si/works/thomas-aquinas-summa-theologica-first-half/663/
cite: "Thomas Aquinas, tr. Fathers of the English Dominican Province, Summa Theologica, First Half, section 663. Scriptura (scriptura.si), https://scriptura.si/works/thomas-aquinas-summa-theologica-first-half/663/"
---

# Summa Theologica, First Half

*Thomas Aquinas, tr. Fathers of the English Dominican Province*

God and creation, human action, law and grace, then faith, hope, charity and justice.

## 663. I–II · Q. 75, Art. 2: Whether sin has an internal cause?

Source: https://scriptura.si/works/thomas-aquinas-summa-theologica-first-half/663/ · cite a paragraph as https://scriptura.si/works/thomas-aquinas-summa-theologica-first-half/663/#p-N

[¶0] Whether sin has an internal cause?

[¶1] 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.

[¶2] 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.

[¶3] 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.

[¶4] On the contrary, Augustine says (De Duabus Anim. x, 10,11; Retract. i, 9) that "the will is the cause of sin."

[¶5] I answer that, As stated above (A 1), 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 77, A 1). 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.

[¶6] But since we have said above (A 1, 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.

[¶7] 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.

[¶8] 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.

[¶9] 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.

### I–II · Q. 75, Art. 3: Whether sin has an external cause?

[¶11] Whether sin has an external cause?

[¶12] 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.

[¶13] 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.

[¶14] 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.

[¶15] 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.

[¶16] I answer that, As stated above (A 2), 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 9, A 6; Q 10, A 4), none can move the will inwardly save God alone, who cannot be a cause of sin, as we shall prove further on (Q 79, A 1). 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.

[¶17] 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.

[¶18] 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.

[¶19] 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.