On the contrary, depending on the couple doing nothing is a surefire way to get pregnant. The problem is you are disassociating our part in creation from conception. Whenever a person has sex knowing they are (or may be) fertile they are, with full knowledge, engaging in an act whose natural consequence is conception. So, to have sex during ones fertile period is not a non-action either way but actually a positive action towards conceiving. So, to try to claim this is the right path for everyone is to try and convince others that even if they have legitimate reasons for avoiding they should take an action that naturally results in conception, knowing that it naturally results in conception even though they have carefully discerned that doing so would be imprudent because they should just “leave it up to God”. On the contrary, they are not leaving it up to God, but would be putting God to the test by taking such an action. While its true that one does not need to practice NFP, all spouses are called to “responsible” parenthood, which means they need to use their own reason and prudential judgement to discern whether or not it is prudent to have children at any given time, and, if it is not, they are obliged to abstain, whether periodically or completely. It is not ok for either spouse to engage in imprudent behaviour for their own pleasure.
Oh, were it true that “depending on the couple doing nothing is a surefire way to get pregnant.” No, that is not true. This is the kind of presumption that gets those of us with no or few children looked at as if we must use a diaphragm on top of the Pill. Not everyone is so fertile as all of that! Before birth control was widely available, women with few children were looked upon as having fewer blessings. Now there are not a few people who feel entitled to believe them to be selfish and worldly, because they don’t have at least three or four. Well, that isn’t the way it works, especially if you didn’t find your husband while you were still in school!! The median age of first marriage for women was 20.3 in the US in 1960. In 2010, it was 26.1. No, women cannot just assume they can get married at 28 and automatically get a baby because they’re healthy. It doesn’t work that way.
This is a weird thread. Why on earth would anybody assume that every good faithful Catholic married couple out there must be either trying to conceive or trying not to conceive, as if the vocation of marriage cannot be lived well unless the couple is constantly obsessing over their chances of pregnancy? That’s not true!
If a couple is actively trying to conceive, knowing that their clock is ticking, then they are wise to chart and actually to abstain for a few days before the fertile time, so that the husband will be more fertile, too. Such a couple will undoubtedly find themselves interiorly encouraged to find a mood once in awhile where they might otherwise not. It’s not as if the time of maximum fertility were two weeks out of the month! Conversely, if a couple is actively trying to avoid conceiving, then of course the natural cycle can be used with intelligence to raise the odds of that, too.
Still, presumably both spouses know where babies come from and they can both decide to just have a married life *without *(gasp!

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any charting, which Catholics have done for centuries. There is nothing irresponsible or closed to life to that, it does not automatically betray a “Providentialist” attitude, or any of the rest. Yes, they’re far more likely to conceive than if they were trying to avoid it, but also less likely to conceive than if they were trying to conceive. That is OK. A married couple is allowed to give up worrying and just live their life without obsessing about whether or not they’re going to have another child–that is OK!