Forlorn, there is no reason to say that a married couple must have the intent to conceive. I think that teaching is "open to the possibility of conception".
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I can honestly say that I never had the intention of conceiving when I was fertile (back in the olden days). In spite of not having the intention of conceiving I conceived and was happy to be a mother.
"Open to Conception" is Novus Ordo crappola; it's basically code-word for, hey, if the condom leaks during intercourse, I won't have an abortion. So you could be open to life while using artificial birth control ... in their mind.
Sure, not many people have the explicit intention of conceiving each and every time they have relations, but there's a virtual intention there anyway. In fact, you could even think, "Boy I really hope she doesn't conceive right now."
What's at issue is forming the positive intention to avoid conception while having sɛҳuąƖ intercourse. It's what Pius XI condemns as the subordination of the primary end of marriage.