The trouble about the Christian standard of chastity is that it isn't and never has been generally lived by; not that it would be profitless if it we… - G. E. M. Anscombe

Intention appears to be something that we can express, but which brutes (which e.g. do not give orders) can have, though lacking any distinct expression of intention. For a cat's movements in stalking a bird are hardly to be called an expression of intention. One might as well call a car's stalling the expression of its being about to stop. Intention is unlike emotion in this respect, that the expression of it is purely conventional; we might say 'linguistic', if we will allow certain bodily movements with a conventional meaning to be included in language.

If a kind of love cannot be commanded, we can't build our moral theology of marriage on the presumption that it will be present. Its absence is sad, but this sadness exists, it is very common. We should avoid, I think, using the indicative mood for what is really a commandment like the Scout Law ("A Boy Scout is kind to animals" - it means a Boy Scout ought to be kind to animals). For if we hear: "a Christian couple grow in grace and love together" doesn't the question arise "supposing they don't?" It clears the air to substitute the bite of what is clearly a precept for the sweetness of a rosy picture. The command to a Christian couple is: "Grow in grace and love together." But a joint command can only be jointly obeyed. Suppose it isn't? Well, there remains the separate precept to each and in an irremediably unhappy marriage, one ought still to love the other, though not perhaps feeling the affection that cannot be commanded. Thus the notion of the "marriage debt" is a very necessary one, and it alone is realistic: because it makes no assumption as to the state of the affections. Looking at the rightness of the marriage act like this will help in another way. It will prevent us from assuming that the pleasant affection which exists between a happy and congenial pair is the fulfilment of the precept of love. (It may after all only be a complacent hiving off together in a narrow love.) We ought absolutely not to give out a teaching which is flattering to the lucky, and irrelevant to the unhappy. Looked at carefully, too, such teaching is altogether too rigorist in a new direction. People who are not quite happily married, not lucky in their married life, but nevertheless have a loyalty to the bond, are not, therefore, bound to abstain from intercourse.

A severe morality holds that intercourse (and may hold this of eating, too) has something wrong about it if it is ever done except explicitly as being required for that preservation of human life which is what makes intercourse a good kind of action. But this involves thoroughly faulty moral psychology. God gave us our physical appetite, and its arousal without our calculation is part of the working of our sort of life. Given moderation and right circumstances, acts prompted by inclination can be taken in a general way to accomplish what makes them good in kind and there's no need for them to be individually necessary or useful for the end that makes them good kinds of action. Intercourse is a normal part of married life through the whole life of the partners in a marriage and is normally engaged in without any distinct purpose other than to have it, just as such a part of married life.