What Do We Mean When We Say the Fetus Is a "Person"?

Francis Beckwith explains:

According to the substance view, the human being is a particular type of living organism—a rational moral agent—that remains identical to herself as long as she exists, even if she is not presently exhibiting the functions, behaviors, or current ability to immediately engage the activities that we typically attribute to active and mature rational moral agents.

Because the human being is a rational moral agent, she is a person of intrinsic moral value as long as she exists.

When I say that the fetus is a person I mean to say that she is just as much a bearer of rights as any person whose rights-bearing status is uncontroversial, e.g., her mother, you, or me. That is, the fetus is entitled to all the rights to which free and equal persons are entitled by virtue of being free and equal persons.

So, for example, one cannot deprive the standard fetus of her life without the sort of justification we would expect if we were depriving a standard ten-year-old of his rights.

To illustrate, if it is wrong to kill a ten-year-old as a result of taking his kidneys and giving them to people the government thinks will benefit society (e.g., scientific geniuses on the verge of curing cancer or AIDS), it is wrong to kill a 20-week-old fetal-clone as a result of taking his kidneys and giving them to his genetic progenitor, a scientific genius, who needs them to survive so that he may continue his work on cures for cancer and AIDS.

From Francis J. Beckwith, "The Human Being, a Person of Substance," in Persons, Moral Worth, and Embryos: A Critical Analysis of Pro-Choice Arguments, ed. Stephen Napier (Dordrecht: Springer, 2011), 67-83; emphasis added.

For further philosophical defense of this position, see Beckwith's Defending Life: A Moral and Legal Case Against Abortion Choice (CUP, 2007) and George's and Tollefsen's Embryo: A Defense of Human Life (Doubleday, 2008). For a more popular-level explanation, see Klusendorf's The Case for Life: Equipping Christians to Engage the Culture (Crossway, 2009).