Summa summae S. Thomae, Tomus II

I say ¹: Sin is rightly defined by Aug., lib. XXII contra Faustum, c. 27: « A word, deed, or desire against the eternal law. »

It is proved. That definition is good which explains the material and formal element of the thing defined; for by these both is the thing distinguished. But, when it says, word, deed, or desire, the material element of sin is explained, which is the human act. When it says, against the eternal law, the formal element is explained; for from this the act is sinful, namely that it is against the eternal law.

[You will object: This definition does not apply to every sin. Therefore it is not legitimate. — Proof of the antecedent. This definition does not apply to the sin of omission, which is not a deed, etc. Therefore it does not apply to every sin.

I answer. I deny the antecedent. — To prove it, again I deny the antecedent. In morals, affirmation and negation are reduced to the same genus. But omission is a negation, or rather the voluntary privation of an act owed, which act is a kind of affirmation; for in voluntary and culpable omission there is an unwillingness to obey, and thereby a will of resisting the law. Therefore omission cannot be voluntary, nor consequently culpable in the individual, without some act which is its cause or occasion, not on the part of the work, but on the part of the worker. Therefore, by reason of this act or deed, it is fitly comprehended under this definition of sin. Therefore this definition is legitimate.]

I say 2°: It is essential to sin that it be an injury and offense of God.

It follows from the preceding. For it is essential to sin that it be against the law of God, as was said. But he who knowingly and willingly acts against the law offends the lawgiver, because he contradicts his will, and refuses him the obedience and subjection owed.

And from this you will gather that there cannot be given a merely philosophical sin, that is, one which is only against reason and not against God, nor an offense of him.

(It seems that, if the matter be considered in the abstract, philosophical sin could be distinguished from theological sin. For St. Thomas says, 1ª 2°, q. 71, a. 6. ad 5: « By theologians sin is considered principally according as it is an offense against God, but by the moral philosopher according as it is contrary to reason. » But this must be understood only hypothetically or conditionally, as is clear from these words of his, 2. 2., q. 20, a. 3, c: « If conversion to a changeable good could be without aversion from God, although it were inordinate, it would not be mortal sin. »

And he brings this reason in the same place: « In every mortal sin the principal reason of evil and gravity is from this, that it turns away from God. » Therefore, if conversion to a changeable good could be without aversion from God, sin would not be theological, but only philosophical, as « disagreeing with rational nature alone and right reason. »

I say: Merely philosophical sin cannot in fact exist.

It is proved 1° from the condemnation by Alexander VIII issued on August 24, 1690, against the following proposition, which Arnaldus had fabricated by twisting certain texts, so that he might attribute it, after his manner, to his adversaries: « Philosophical or moral sin is a human act disagreeing with rational nature and right reason; but theological and mortal sin is the free transgression of the divine law. Philosophical sin, however grave, in him who either does not know God or does not actually think of God, is a grave sin, but it is not an offense of God, nor a mortal sin dissolving the friendship of God, nor worthy of eternal punishment. » — This proposition was « declared and condemned as scandalous, temerarious, offensive to pious ears, and erroneous. »

It is proved 2° by reason. According to Augustine, theological sin is « a word, deed, or desire against the eternal law, » and as the Angelic Doctor observes in the former place related above, « Augustine defines sin more fittingly from this, that it is against the eternal law, than from this, that it is against reason, especially since by the eternal law we are regulated in many things that surpass reason. » Whence it follows that we are regulated by this law also in those things which pertain to reason. But whenever anything is done against right reason, the eternal law is injured. Therefore such an act is theological sin. — Proof of the minor. 1° Right reason is nothing else than a participation of the eternal law, or an intellectual light manifesting to us the eternal law. Therefore no one can act against right reason without at the same time injuring the eternal law.

If you object that he who acts against right reason may not attend to the eternal law, and consequently cannot injure it in any way, I answer that no one is ignorant of this principle of the eternal law: « Evil is to be avoided. » But whoever acts against right reason knows and necessarily advertes that his action is evil; for it is supposed that he spurns the dictamen of conscience. Therefore he injures the eternal law. Therefore theological sin is admitted.

2° From the very name it is understood that theological sin is committed against God. For he who knowingly acts against right reason commanding or forbidding perceives that he subverts the natural order, and knows at least implicitly that this order was established from eternity by the supreme legislator, that is, by God. Therefore he sins against God himself. Therefore such sin is theological.]