Does there come a point in a marriage when the couple should (or perhaps are obligated to) cease engaging in the marital act?

I'm thinking of situations like during pregnancy, after menopause, etc., when it is absolutely (barring a miracle) certain that conception cannot occur.  It would seem that the couple could possibly fall into using the marital act strictly for lust, which is sinful.  Perhaps they are de facto using it for strictly for lust in these situations.

Thoughts?

The *primary* purpose of the marital act is the procreation of children. Note the word primary. Not the sole or only purpose. The secondary purpose of the marital act is unitive and preventing concupisence.

You must look at the whole picture of Catholic sɛҳuąƖ morality for it to really make sense.

 You cannot have unitive without procreative (contraception) and you can't have procreative without unitive (in vitro), for example.

I hear what you're saying, but taking your examples a step further, if a woman is already pregnant or is post-menopausal, would the marital embrace not be, by definition, in those cases "unitive without procreative"?

My understanding of this is that the marital act is primarily for procreation and secondly to prevent one (or both) of the spouses' from committing adultery.  If post menopausal couples are at risk for using intimacy in a lustful way, then I suppose not having intimacy might increase the risk of one or both of them pursuing an adulterous relationship to have these "needs" met.  

However, if both spouses are advanced spiritually and agree that they want to separate and join a monastery / convent for the rest of their lives that would be different.  But both must agree with this plan and probably have to get a dispensation from living in the conjugal state from the bishop (but I don't know exactly how this would work).  If one of the spouses' is not in agreement, the other spouse would have to stay in the home and continue to render the marital debt as required.  

Does there come a point in a marriage when the couple should (or perhaps are obligated to) cease engaging in the marital act?

I'm thinking of situations like during pregnancy, after menopause, etc., when it is absolutely (barring a miracle) certain that conception cannot occur.  It would seem that the couple could possibly fall into using the marital act strictly for lust, which is sinful.  Perhaps they are de facto using it for strictly for lust in these situations.

Thoughts?

Does there become a point in a marriage?  Yes.  Does there become a point in every marriage?  No.

The instances you have given aren't really the instances that come to mind, I'm thinking more like after a traumatic surgery or for some other medical reason (besides pregnancy or menopause) where the marital act would pose some health risk to one or both spouses.  The marital debt can be postponed for a just cause.

A woman cannot conceive when she is not ovulating.  Barring a miracle, it is certain that conception cannot occur.  Women don't always know when they're ovulating, and the men certainly don't.  Ironically, if one is intent on discerning ovulation patterns, doing so will likely involve NFP-style charting.  But there is no Church teaching that says married couples can only be intimate when the woman is ovulating-- because the Church teaches that procreation is the primary end, not the only end of marriage and the marital act.  This has already been mentioned, and it's the key to understanding this entire concept.

One of the second ends of the procreative act is the satisfaction of concupiscence.  The Church recognizes the frailty of human nature especially in relation to sins of the flesh, and one purpose marriage serves is as a licit avenue by which the passions can be exercised.  This is obviously, in comparison to the dignity of participating with God in bringing forth new life, a more base function of the act, but it is a legitimate function of it nevertheless.  A couple who marry promise each other exclusive and perpetual rights to their respective bodies, not simply rights until the woman enters menopause.  Nor does the right disappear when the woman becomes pregnant.

What about the situation where a man or woman has themselves voluntarily sterilized, but then converts and/or repents?  In that case wouldn't any future engagement in the marital act be artificial contraception, and thus evil?

In these cases the couple is not deliberately frustrating the procreative end.

Sorry, accidentally disliked this post.

sterility is not an impediment to marriage.

The answer is that the marital act would still ne licit.  I presded send too soon.  I'm on my phone. Ill post more after work.