Article II: On the Sin of Omission Negatively Voluntary

St. Thomas, I-II, q. 71, a. 5; De Malo, q. 2, a. 1.

419. What the sin of omission is. - A sin of commission is the placing of a prohibited act, and is opposed to a negative precept; a sin of omission is the non-placing of a prescribed act, and is opposed to an affirmative precept.

This sin of omission in itself, that is, considered in its essence, is not an act but a mere privation; nevertheless it supposes some positive act, at least interior, joined or preceding, which is its cause or occasion, by which, namely, someone directly wills to omit the prescribed thing, or directly wills, whether now or before, something else by which he is impeded from doing that which he ought. For omission, in order to be sin, must be directly voluntary, either according to itself, as if someone wills not to hear Mass, or at least in the cause, as if he directly wills to place an act incompossible with the prescribed thing, whether joined, for example, if he wills to play when he ought to hear Mass, or preceding, as if he wills to stay awake long in the evening, from which he foresees that he will not hear.

1. Nevertheless, it is better said that the sin of omission is without an act. Cf. above, p. 67, note 1.

420. When does a sin of omission occur? - A sin of omission is begun interiorly and contracted as to affection and fault when the cause of the omission is voluntarily placed: for then the one omitting either voluntarily intends not to fulfill, or voluntarily exposes himself to the danger of not fulfilling; it is consummated exteriorly and placed effectively when the time for fulfilling the precept is present and it is not fulfilled.

This exterior omission adds no malice per se to the interior act; nevertheless it is sin (and therefore to be declared in confession), as being voluntary disorder, in the same mode as an evil external work is rightly called sin. But if someone has sincerely and efficaciously retracted the will of omitting before the external omission follows, this will not be sin but only the materially evil effect of sin, for example, one who threw the breviary into the sea and afterward on the journey repents.

421. Is the work placed at the time of omission a sin? - The work which is placed at the time of omission, if it is its cause or occasion, is sin, yet not distinct from the omission (and consequently not to be declared in confession), but evil with the very malice of the omission: thus play which is the cause of the omission of Mass. If it is not the cause of the omission but is related to the omission merely accidentally and concomitantly, unless it is evil from elsewhere, it will not be evil, nor from the omission: thus if someone has efficaciously resolved not to hear Mass, but lest meanwhile he remain idle, applies himself to study.