Promiscuity requires abortion, and here is why. Consider what it means to raise a child. For the mother, this begins with bodily discomfort, sometimes extreme, some subtraction from her physical health and beauty, complete emotional involvement, and many sleepless nights to walk with a baby with colic or for simple breastfeeding. And that is just the first year. For the father, this implies a permanent commitment to the child's mother, sweat and hard work, sacrifice of sleep and time as well, constant attention to the child's character and education, and putting the child first, before friends or amusements. These commitments and sacrifices stretch to 25 years or more.

Now suppose someone gets drunk at a party and "hooks up" with someone afterwards in a hotel room, whose name he or she does not even know, shakes off the thing the next day, and then in a couple of weeks is told that, because of that event, he or she is now committed to making all of the sacrifices I just described.

We must all agree that this makes no sense. The effect does not match the cause. The context does not match the result. Something, therefore, has to give, and since, given bad habits and culture, it is very difficult to conclude immediately that the promiscuity is wrong and somehow needs to be "repented of" -- well then, it just "has to be the case," somehow, that abortion is an acceptable remedy -- either because there really is not a child yet (just a "clump of cells") and the incongruity can be stopped before it arises, or that a person has a "right" to define the universe as he wants (as Justice Kennedy asserted in Casey) and make this nonsense look like sense by negating that absurd commitment.

When A contradicts B, the contradiction may be addressed by either eliminating A or eliminating B. A 25-plus year commitment to another person contradicts the complete lack of commitment to this person shown in casual sex. Thus, if we hold onto the promiscuity, it is necessary to eliminate the child.

The MIT philosopher Judith Jarvis Thompson wrote an essay -- the most widely-read essay on abortion assigned, approvingly, at colleges -- where she argues that being pregnant is like waking up one morning and finding that you have been turned into a living dialysis machine, because during the night a stranger was hooked up to you month's long for kidney support: you'd be within your rights, she says, to disconnect the stranger, and similarly a pregnant woman is within her rights to "disconnect" the fetus.

Pro-life people have raised objections to the argument in vain. The unborn child is not a stranger, they say, but the mother's very son or daughter. That child is not merely "disconnected" from the mother but poisoned or dismembered. Except in cases of rape, they say, the woman gets pregnant as a result of her choice: the baby is not mysteriously inserted into her apart from her own actions. But these objections are all in vain if we presuppose, as a fundamental commitment, sexual promiscuity.

What Thompson and those who agree with her are especially loathe to grant is that the child is the result of the woman's choice. In a promiscuous culture, the first intuition to go is that sex is fundamentally a procreative act, that its very purpose is to beget children. If that is its purpose, then it is no more surprising that people who engage in sex should eventually get pregnant, despite their precautions, than that someone who builds a house under water might eventually face leaks.

But -- grasp this-- in a promiscuous culture it can look arbitrary that a child results from sex at all. One supposes, instead, that if people took reasonable precautions, like use a condom, then it would be perverse to hold them responsible if they conceive a child.

So, promiscuity requires abortion. And there is no mystery as to why the Supreme Court discovered a right to abortion about 10 years into the sexual revolution. Forget all the business about the "right to privacy," and so on, which is mere rationalization: freedom understood in that particular way makes no sense unless abortion makes sense.

I wish to place before you two implications. The first involves the culture of life. A Catholic's practice of the culture of life must go considerably deeper than opposition to abortion. It must extend to everything connected to the culture of promiscuity, which we should be adept to recognize now as one aspect taken by the culture of death. It must extend to the institutions we support, and to the media we watch for entertainment. For instance, if we would not watch a putative romantic comedy in which the romantic leads plot an abortion together, then we should similarly not watch a story which culminates in their hopping in bed. Supply in thought "abortion" whenever casual sex is celebrated in pictures or in song, and you will not be far from the mark. Be as much an enemy of the one as you are to the other.

A second involves the Catholic conception of social justice. If abortion is the primary violation of social justice in our society today, and if promiscuity makes abortion necessary, then it becomes an imperative of social justice to practice those virtues directly opposed to promiscuity, namely, modesty, chastity, and purity.

Michael Pakaluk is professor and chairman of philosophy at Ave Maria University and a member of the Pontifical Academy of St. Thomas Aquinas.