245. Just as we distinguished above between bad thoughts and thoughts on things that are bad, so may we distinguish between bad desires and desires of what is bad. For bad desires that are not mere velleities are sinful, as we have just seen; whereas the desire of what is physically evil is good, if the evil is wished, not for its own sake, but for the sake of some greater good. Example: To desire out of hatred that a neighbor lose his arm is a bad desire and sinful; but if one wished this as a means to save the neighbor’s life, while he still desires something evil, it is not the evil but the benefit that is intended, and hence the desire itself is not bad.
246. The Causes of Sin.—The causes of sin are partly internal (i.e., those which are in man himself) and partly external (i.e., those which are without).
247. The internal causes of sin are: (a) ignorance in the intellect; (b) passion in the sensitive appetites; (c) malice in the will.
248. Since ignorance and passion may render an act involuntary (see 40 sqq.), the sins that result from them are of two kinds, viz., material and formal. (a) Material or objective sins are transgressions of the law that are involuntary, and consequently not imputable as faults. Examples: Blasphemies uttered by one who is delirious or hypnotized; breaking of the fast by one who is inculpably ignorant of the law; imprecations pronounced by a person out of his mind through fear. (b) Formal or subjective sins are transgressions of the law that are voluntary, and hence imputable as faults. They are not only against the law, as is the case with material sins, but they are also against conscience.
249. Ignorance, passion and malice cause sin as follows:
(a) Every sin results from practical error (i.e., from a wrong decision as to what one should do here and now), for the will chooses wrong only after the intellect has decided on wrong. In this sense, then, it is said that all who sin are in error (Prov,, xiv. 22), and that every sinner is in ignorance (Aristotle, _Nich. Ethics_, Bk. III, c.1, 1110b 27). But not every sin results from speculative error (i.e., from a false notion or judgment about the lawfulness of an act in general). else we should have to hold that everyone who sins is in error against the faith;
(b) Speculative ignorance causes formal sin, when the ignorance is culpable and leads to wrongdoing, as when a person has never taken the pains to learn what the law of fast requires and in consequence violates the law, or when an automobilist through carelessness does not see a person crossing the street and runs him down. Speculative ignorance causes material sin, when the lack of knowledge is inculpable and leads one to do what one would not otherwise do, as when a child shoots a playmate, not knowing that this is a sin, or a soldier shoots a comrade whom, on account of darkness, he mistook for an enemy spy;
(c) Passion, by clouding the judgment and vehemently inciting the will, leads one to act against one’s better knowledge and to choose inordinately the concupiscences of pleasure, or possessions, or glory (I John, ii. 16). If the passion is voluntary, the resulting sin is formal; but, if the passion is involuntary and takes away the use of reason, the sin caused is material;
(d) Malice is found in a sense in every formal sin, inasmuch as every sin is committed out of choice. But malice in the strict sense, as here understood, is a choice of sin made, not on account of preceding ignorance or passion, but on account of some corrupt disposition of the sinner which makes sin pleasing or acceptable to him, such as a vicious habit or inclination which he cultivates, or willful despair or presumption which he entertains.
250. Ignorance and passion do not always make an act involuntary (see 40 sqq.), and hence three kinds of formal sins may be distinguished according to the three kinds of causes from which they proceed: