I am beginning to suspect that some posters don't actually know what NFP is. It is the practice of discerning a woman's pattern of ovulation by certain (variable) methods.
Why would you even want to know when the ovulations start and stop , if it wasn t for the fact that you want to know when you can do the marital act, supposedly so you can escape having Children. (NFP).
If you follow the teaching of he Church and PPXI, it wouldn t matter when they fall. Every desire to copulate by both should be to that God will give you another member to your family. If that is not your desire , then contenience is the only way to go. That s what the Church teaches.
It all starts with what is in the Plan. Whats in your mind before the action.
If you had read my whole post, you would have read where some couples use NFP so that they know
when to have relations, rather than when to avoid them.
As to the bolded, it
should be the desire, yes. But the Church does not teach that married couples must be motivated by an explicit intellectual assent to conceive in order to have licit marital relations. Their motivation for relations does not need to be driven by a front-most desire to have children.
This is why St. Paul says it is better to be married than burnt. Yes, it is better to be a virgin (and not to marry at all) but for those who cannot abstain, better they be married where they can exercise their passions licitly and to a good end, rather than to carry on in fornication. He describes marriage as a way to exercise concupiscence without any reference to procreation.
Furthermore, St. Augustine teaches the same:
"...what is it which the apostle allows to be permissible, but that married persons, when they have not the gift of continence,
may require one from the other the due of the flesh— and that not from a wish for procreation, but for the pleasure of concupiscence? This gratification incurs not the imputation of guilt on account of marriage, but receives permission on account of marriage. This, therefore, must be reckoned among the praises of matrimony; that, on its own account, it makes pardonable that which does not essentially appertain to itself. For the nuptial embrace, which subserves the demands of concupiscence, is so effected as not to impede the child-bearing, which is the end and aim of marriage (On Marriage and Concupiscence, Book I ch. 16)."
So, the Church does not teach that marital relations must always be motivated by a desire to conceive. Of course, willfully frustrating conception is a grave sin against the natural order, but there is a difference between willfully frustrating conception and simply not thinking of it, or even being afraid of it.