476、⑿在与情妇或妾的关系存续期间，与妻子发生性关系是不合法的。原因在于，婚姻之爱本身是属灵的，贞洁、纯粹和神圣，若变得属世，就会被污染，变得衰弱，从而灭亡。所以，为了保存这爱，出于纯正重大理由（472，473节）找情妇或纳妾就成了权宜之计，但只能找一个，不能同时找两个。
476、（12）因为这种情况下，若不禁止，婚姻之爱的精神性，贞洁性，神圣性就会受到侵蚀，会消失。因此为了保护这种爱，要避免与二者同时存在关系。
476. (xii) So long as a man has a concubine of this kind, sexual relations with his wife are unlawful.
The reason is that conjugial love, which is in itself spiritual, chaste, pure and holy, then becomes natural, being so polluted and enfeebled that it dies off. In order to preserve this love it is important that for genuinely weighty reasons (472-473) only one concubine is taken, and not two at once.
476. 12. As long as this relationship with a mistress continues, physical conjunction with the wife is prohibited. It is prohibited because in such an event, conjugial love, which in itself is spiritual, chaste, pure and sacred, becomes natural, defiled and stale, and thus perishes. Therefore, in order to preserve this love, it is proper that the relationship in taking a mistress for real weighty reasons (nos. 472, 473) be carried on with the one, and not with both at the same time.
476. 12. While this concubinage continues, sexual union with a wife is not permissible. The reason is that then married love, which per se is spiritual, chaste, pure, and holy, becomes worldly, is degraded, decays, and is lost in this way. So for this love to be kept safe, having a concubine for important, valid reasons (nos. 472-473) has to be done with one woman, and not with two at once.
476. XII. THAT WHILE THIS CONCUBINAGE CONTINUES, ACTUAL CONJUNCTION WITH THE WIFE IS NOT LAWFUL. The reason is because in such case conjugial love, which in itself is spiritual, chaste, pure and holy, becomes natural, is contaminated and worn out, and thus perishes. Wherefore, that this love may be preserved, it is expedient that concubinage from really weighty causes (nos. 472, 473) be with one only and not with two at the same time.
476. (xii) While this concubinage lasts, actualized union with the wife is not permissible. For in that event marital love, which in itself is spiritual, chaste, pure and holy, becomes natural, is contaminated and cast off, and thus perishes. That this love may be preserved, therefore, it is expedient that concubinage for weighty and real causes (n. 472-473) be with one only and not with two at the same time.
476. (12) That while this concubinage lasts, actual conjunction with the wife is not lawful. The reason is that then conjugial love, which in itself is spiritual, chaste, pure, and holy, becomes natural, is defiled, becomes obsolete, and thus perishes. Therefore, in order that this love may be preserved it is expedient that for real weighty causes (n. 472, 473) concubinage may be resorted to, but only with one, and not with two at the same time.
476. XII. Quod quando hic concubinatus perstat, actualis conjunctio cum uxore non licita sit. Causa est, quia tunc Amor conjugialis, qui in se est spiritualis, castus, purus, et sanctus, fit naturalis, contaminatur, et obsolescit, et sic perit; quare ut hic amor conservetur, expedit, ut concubinatus ex causis sonticis realibus, 472, 473, fiat cum una, et non cum duabus simul.