(d) It is voluntary directly or indirectly: directly, when one intends it as an end (e.g., for the sake of the pleasure) or as a means (e.g., as a relief from temptation or bodily itching, to obtain a specimen of semen for medical diagnosis); indirectly, when one unjustifiably does something from which one foresees that pollution will result. In all these cases pollution is formal or sinful, and it is not to be confused with material or natural pollution, which is a discharge of semen or distillation that is involuntary or unimputable.
2536. Cases of Material or Non-Sinful Pollution.—(a) Involuntary pollution is passive or active. The former happens even when one is awake. It is evoked by such slight causes as physical movement and exertion, and is unaccompanied by pleasure; when habitual, it is a disease due to organic debility The latter happens during sleep, and may be caused by a superfluity of fluid. It is accompanied by pleasure and often by libidinous dreams. It is a means used by nature to relieve the system, and is therefore healthful and beneficial, unless the discharges are too frequent (e.g., nightly). There is no obligation of repressing the continuance of a pollution that began involuntarily during sleep, since it may be regarded as an act of nature; but consent must be withheld (2498 sqq.). Moreover, if merely natural pollution be considered, not as to its venereal gratification but solely as to its good effects (e.g., that it ends a temptation, that it benefits the mind or the health), there is no sin in rejoicing at its accomplishment or in desiring its fulfillment, provided nothing is done to produce it and the intention is good; for then the object of the will is indifferent and the end is good.
(b) Unimputable pollution is caused by a lawful act from which one foresees that pollution will ensue, there being no proximate danger of consent to sin, and the pollution being only permitted, and that for a proportionately grave reason.
2537. Unimputable Pollution.—In reference to unimputable pollution the following distinctions should be noted:
(a) the danger risked by an act may be either of formal pollution (i.e., with consent to sin) or of material pollution (i.e., without consent to sin);
(b) the danger of pollution is either proximate or remote, the former being that from which pollution naturally and usually results and the latter that from which it does not naturally or usually result. Remotely dangerous are acts of a non-venereal kind, such as horseback riding, gymnastics, drinking alcoholic beverages, and also acts of a sexual kind that are only mildly exciting, such as conversations or books that are slightly “off color” when the parties are of mature age (see 2517, 2518). Proximately dangerous are acts of a venereal kind that notably inflame passion, such as warm and lingering kisses between persons of opposite sexes (see 2517, 2518);
(c) the reason for running the danger of pollution is either grave, serious, or slight. A grave reason is real necessity (e.g., the removal of disease or pain or of a very painful or troublesome itch due to the blood or disease) or great utility (e.g., the preservation of health, cleanliness of body); a serious reason is an important convenience of soul or body (e.g., the exercise of common politeness, the enjoyment of reasonable comfort); a slight reason is one in which none of the mentioned motives is found (e.g., the satisfaction of an idle curiosity, the removal of a trifling irritation or itch).
2538. Proximate and Remote Occasions of Pollution.—It is never lawful to expose oneself to the immediate danger of sin, for he who loves the danger loves the sin (see 258, 260); but if one uses means to make the danger remote, one may lawfully encounter it for a good reason (see 258, 260, 261). It is lawful to permit an evil effect when there is sufficient justification according to the principle of double effect (see 103 sqq.).
(a) Hence, if there is proximate danger of formal pollution (that is, of consent to sin), no reason excuses an act even of a non-sexual kind, such as horseback riding. But if the act is necessary, the danger must be made remote by the use of special means, such as prayer, firm resolves, etc. (see 2497 sqq.).
(b) If there is proximate danger of material pollution, a grave reason suffices (e.g., the care of patients by physicians and nurses, assistance of bathers by attendants, warm soporific drinks taken for the sake of sleep).