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The Uncertainty Principle

If abortion might kill a person, then abortion must not be done.

The Uncertainty Principle: If abortion might kill a person, then abortion must not be done.

Page Summary:

Uncertainty in regard to life's beginning has long been used as an argument in favor of legal abortion. In reality, if any uncertainty exists, abortion ceases to be a justifiable option.

Uncertainty is at the heart of legal abortion in the United States. It was on the assertion that life's beginning is unknowable that the Supreme Court struck down all state prohibitions against abortion.1 In the decades that have followed that 1973 verdict, countless abortion advocates have taken up this same refrain. It goes like this: since we don't know when human life begins, women must be free to make up their own minds about abortion.

There are two problems with the above conclusion. First, as we've already demonstrated, the biological beginning of human life is knowable and has been for a long time. It is only when life is defined according to subjective metaphysical benchmarks that its beginning becomes fuzzy. And here again, there are numerous problems with attaching the notion of personhood to traits like rationality or sentience.

The second problem with arguing for abortion on the basis of uncertainty is this. It's a logical absurdity. Even if we allow for the assertion that the beginning of human life is unknowable, that is not a point in favor of legal abortion. It is a point decidedly against it. In order for abortion to be justified, there must be absolute certainly that it does not kill a human person. Peter Kreeft, a professor of philosophy at Boston College, points out that there are only four possibilities with regard to abortion.2 They are:

  1. The fetus is a person, and you know that.
  2. The fetus is a person, but you don't know that.
  3. The fetus is not a person, but you don't know that.
  4. The fetus is not a person, and you know that.

Now consider each of these ramifications in actual practice:

  1. If a fetus is a person and you know that, then abortion is an act of homicide. You intentionally killed an innocent human person.
  2. If a fetus is a person but you don't know that, then abortion is an act of manslaughter. You unintentionally killed an innocent human person.
  3. If the fetus is not a person but you don't know that, then abortion is an act of criminal negligence. You didn't kill an innocent human person, but you intentionally risked doing so.
  4. If a fetus is not a person and you know that, then abortion is an act that needs no justification. You did nothing more significant than getting a haircut or removing your tonsils.

Notice that only one of the above scenarios justifies abortion, and notice that it is a scenario that does not exist in the real world. No one can say with absolute certainty that abortion does not kill a human person. At best, someone can be strongly convinced that it does not, but they have no capacity to prove so, since their metrics are indistinct and immeasurable.

By contrast, we can say with certainty that abortion kills a human being (i.e. a living, genetically-distinct member of the human species). It is only when you try to differentiate between human beings and human persons that objective classification goes out the window. Abortion advocates make this distinction for the express purpose of introducing uncertainty into the equation. Since the transition between developing human being and functional human person takes place at some unknown point between conception and birth, or after birth as some ethicists maintain, proponents of abortion think they have found a legal loophole. This is simply not so.

Uncertainty as to whether a building is occupied does not give an exterminator the right to fumigate. Uncertainty as to whether an overturned bassinet is empty does not give a truck driver the right to plough through it. Uncertainty as to whether a walk-in freezer has been vacated does not give a night manager the right to lock and bolt it. Uncertainty as to whether a high climber has moved to another tree does not give a lumberjack the right to fell the timber. And uncertainty over whether a person is really dead does not give a mortician the right to light the furnace. Personal conviction makes no difference. The absence of human life must be completely verified before any of these actions can take place.

In the context of abortion, the burden of proof lies with those who want to justify the practice, not with those who oppose it. It lies with those who seek to exclude a specific subset of the human community from being protected under the law, not with those who believe all human beings should receive equal protection. As such, it is not the responsibility of abortion opponents to prove that abortion does kill a human person; it is the responsibility of abortion advocates to prove that it doesn't. If ANY uncertainty exists, then abortion cannot be justified.

This page was last updated on February 04, 2017. To cite this page in a research paper, visit: "Citing Abort73 as a Source."


  1. The assertion that "[we cannot] resolve the difficult question of when life begins" was made by Justice Harry Blackmun in the majority opinion of Roe v. Wade. 410 U.S. 113. Supreme Court of the United States. 1973.
  2. Peter Kreeft, "The Apple Argument Against Abortion," Crisis Magazine, December 2000, http://www.peterkreeft.com/topics-more/personhood_apple.htm

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