We had an impassioned response to a recent article, entitled Traditionally Conservative Feminism, concerning the use of contraception in marriage. Although the response was based upon the correct rule that a Catholic should never use contraception, even if the spouse requires it, the comment thread soon showed that the situation becomes more difficult when it becomes a question of whether or not to have sex with a spouse that is using contraception.
Luckily, the Pontifical Council for the Family has already addressed that issue in the Vademecum for Confessors Concerning Some Aspects of Morality of Conjugal Life. The pertinent passage is as follows:
13. Special difficulties are presented by cases of cooperation in the sin of a spouse who voluntarily renders the unitive act infecund. In the first place, it is necessary to distinguish cooperation in the proper sense, from violence or unjust imposition on the part of one of the spouses, which the other spouse in fact cannot resist.46, 561).] This cooperation can be licit when the three following conditions are jointly met:
when the action of the cooperating spouse is not already illicit in itself;47
when proportionally grave reasons exist for cooperating in the sin of the other spouse;
when one is seeking to help the other spouse to desist from such conduct (patiently, with prayer, charity and dialogue; although not necessarily in that moment, nor on every single occasion).
Or, as this article at the NCBC explains:
Thus, while Agnes would not be obliged to facilitate her husband’s sin, she could herself, without sin, engage in marital relations with him if she thought refusal to do so might lead to other sins, such as temptations to infidelity or divorce, as long as she continued to seek and encourage a change of heart and a change of perspective in him.
I hope that clears things up.