II. Circumstance: Why

238. - In this place, the intention by which spouses have endeavored to avoid the generation of offspring must chiefly be considered. They can comply with this intention both by abstaining and by acting: by abstaining, through omitting intercourse on days on which there is greater hope of fertilization, or through declining a better manner of intercourse; by acting, if through an action done for that purpose they place a positive impediment to fertilization, for example, through exercise which gives hope of sterility.

Come now, spouses are altogether prohibited from acting anything, with an intention contrary to the end of nature, by which conception is impeded or rendered less probable; and this under guilt of grave sin, at least if they have judged that they would effect a serious or notable difficulty. But when that use of marriage is made which, considered in itself, is either honorable or only lightly sinful, that act cannot be substantially vitiated if one abstains from a better use lest offspring be generated. For since there exists of itself no positive obligation to generate offspring or to cooperate positively in its generation, this intention, indifferent in itself and capable of becoming positively honorable for just causes, will indeed be blameworthy if, with the circumstances considered, it is infected by self-love; but this vice does not exceed venial guilt. Cf. Noldin, De sexto, no. 68; De Smet, De sponsalibus, etc., no. 209; Aertnys, Theologia moralis, vol. 2; Alberti, De sexto et nono, nos. 125, 130.