The pro-life argument against abortion is quite simple:

(1) It’s always wrong to deliberately kill innocent human beings.

(2) Unborn children are innocent human beings.

(3) Therefore, it’s always wrong to deliberately kill unborn children.

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I think it’s important for pro-lifers to revel in the simplicity of this argument. It does not require any moral sophistication to recognize that direct abortion is murder. And yet it is precisely the putative sophisticates in moral philosophy who so often defend the ghastly practice. They typically employ two main strategies for doing this: first, argue that it is sometimes morally permissible to kill innocents (the so-called woman’s right argument), or second, deny the moral status of the unborn child (the so-called personhood argument).

In this two-part article, I focus on this second strategy in order to show how a key misunderstanding of the pro-life position trades on a false conception of potentiality. Today I lay out challenges to the pro-life argument from abortion defenders and locate the problems with those challenges in their misunderstanding of potentiality. Tomorrow I will correct that misunderstanding, and explain how what Francis Beckwith calls “the substance view of persons” grounds the proper understanding of potential.

When faced with the simple argument above, many abortion defenders begin by insisting on a distinction between human beings and moral persons. They argue that murder does not consist in the killing of an innocent human being, but rather in the killing of an innocent moral person. They claim that these are non-identical sets—that there are human beings that are not moral persons, and (in principle at least) moral persons that are not human beings. Of course, the abortion defender is mainly interested in denying that some (very young) human beings are not moral persons.

Since even very young human beings (zygotes, blastocysts, embryos, etc.) are obviously beings that are human, abortion defenders instead invoke some criteria of moral personhood that they claim human beings do not manifest until they reach a certain level of development. This is a tricky move since they need to choose criteria that are narrow enough to exclude very young human beings but broad enough to include all (or most) classes of individuals that most people intuitively accept as worthy of moral protection, such as newborn infants. A few (Peter Singer and Michael Tooley, for example) have been willing to follow the argument to its logical conclusion and argue that newborn infants are not moral persons, but most abortion defenders (at least those who want to persuade the public) tend to avoid such extremes.

Various writers have proposed different sets of criteria for moral personhood, but most turn on some combination of rationality and sentience (especially the capacity to suffer). In order not to get bogged down in the question of what properties ground moral personhood, let us just label the relevant property or set of properties (assuming there are any) as P. We can then articulate this part of the pro-abortion position as follows:

(A1) All moral persons manifest P.

(A2) Very young human beings (zygotes, blastocysts, embryos, etc.) do not manifest P.

(A3) Therefore, very young human beings are not moral persons.

If this argument were sound it would be enough to falsify the original premise that unborn children are innocent human beings, and thus undermine the simple pro-life argument above (provided that moral persons is substituted for human beings).

Perhaps the natural response is to attack (A2), the premise that very young human beings do not manifest whatever properties are needed for moral personhood (P). But there is an obvious problem for the pro-life position: at the earliest stages human beings clearly do not manifest any higher powers such as rationality or sentience. Therefore, the better response is to reject (A1), the contention that all moral persons manifest P, by taking refuge in the claim that even very young human beings have the potential to manifest P.

In turn, the abortion defender responds by denying, as David Boonin does in A Defense of Abortion, that the “potential possession of a right entails actual possession of a right.” In other words, the abortion defender thinks that the pro-life appeal to potentiality works like this:

(P1) Anything with a potential right to life has an actual right to life.

(P2) Very young human beings possess a potential right to life.

(P3) Therefore, very young human beings possess an actual right to life.

Boonin rightly notes that it “certainly is not true of properties in general that if a given individual potentially has a given property, then the individual already has the property. Prunes have properties that plums do not have, wine has properties that grape juice does not have, and adults have properties that fetuses do not have.” Accordingly, he concludes that (P1) is false; just because a very young human being has a potential right to life, it does not follow that it has an actual right to life.

On this point Boonin is correct; a potential right does not confer an actual right. I might potentially move to Texas from Minnesota and so gain the right to vote there; obviously that potential does not give me the right to vote in Texas now. However, the real issue for the pro-life side is not the truth of (P1), but rather that the pro-life appeal to potentiality is not captured in (P1)-(P3). Instead, a better pro-life position (the substance view of persons) is more accurately captured by:

(P4) Anything that has the potential to manifest P is (always already) a moral person.

(P5) Very young human beings have the potential to manifest P.

(P6) Therefore, very young human beings are (always already) moral persons.

This pro-life position argues not that a potential right entails an actual right, but rather that the potential to manifest P is itself sufficient for personhood. Thus, the pro-life claim is that the fetus is always already an actual person from the beginning of her existence. She does not acquire personhood at some point in her development; insofar as she is a human being she is (always already) a person.

Articulated in this way, the pro-life position avoids the mistake of trying to derive actual rights from the mere potential to possess rights. However, the abortion defenders have a canned response to the pro-life appeal to potentiality that not only reveals their systematic misunderstanding of (P4)-(P6), but also a fundamental misunderstanding of metaphysics. This response consists in offering supposed counter-examples to (P4). Michael Tooley’s reaction to appeals to potential (repeated many times during his career, recently in Abortion: Three Perspectives) is typical: “If one considers the case of a kitten that will, if there is no interference, be injected with a chemical that will transform its brain so that it will have the capacities for thought and self-consciousness, and hence, presumably, a serious right to life, it is clear that [P4] is false, since the kitten, before the injections does not have a serious right to life.”

Boonin offers a similar response:

One could, I suppose, characterize [an anencephalic] fetus as a person whose capacity for thought simply happens to be “blocked” by a contingent fact about its head. But then it is difficult to see why we should not also call the spider crawling up my window a person. If he were able to develop a big enough brain, he too would be able to function as a person, so he is simply a person whose capacity is blocked by the fact that he will never have a large enough brain.

Both the kitten and the spider are offered as supposed counter-examples to (P4) insofar as in each case, the relevant critter supposedly has the “potential” to become a moral person (i.e. to manifest P) and yet is obviously not a person. However, these examples do not actually bear on (P4) at all because both of them evince a complete misunderstanding of what it means to say that something has the potential to manifest P.

Tooley and Boonin understand potential in terms of possible future states of affairs. For them, potentiality is merely (nomological) possibility (as they conceive it, not how it actually is). To say that the kitten or the spider has the potential to be a person means that they can imagine a possible world in which magic injections (or the like) can result in the development of “a big enough brain” for a kitten or a spider to “function as a person.”

Of course all of this is pure fantasy. Not only is there no magic injection that will turn a kitten into a person; such a thing is not even possible in principle because if (per impossibile) a kitten could be turned into a person, it would simply cease being a kitten. In the spider case, “the fact that he will never have a large enough brain” doesn’t “block” anything; by nature, spiders are non-rational creatures. Boonin’s claim is comparable to saying that my potential to be a giraffe is “blocked” by the fact that my neck is too short.

This conception of potential in terms of a future state of affairs is especially clear when Boonin argues that “the claim that every member of homo sapiens has the capacity to function as a person is false. There can, for example, be human fetuses with such severe deformities that they will never develop a brain capable of sustaining thought, or even any brain at all.” Since an anencephalic infant lacks a brain there is no possibility that it will “function as a person”—i.e., there is no possible future state of affairs in which this infant will develop into a normal adult human being (barring Tooley’s magic injection, one supposes).

While the real issue is not species membership, the substance view of persons does hold that even an anencephalic infant has the potential to function as a person, because the correct understanding of potential is not a prediction about the future, but a statement about what kind of thing it is. The abortion defenders’ objections are understandable because they rely on a reductionist view of persons that fails to recognize the proper sense of potentiality as a developmental potentiality. However, when persons are understood as (metaphysical) substances (of a rational nature), these supposed counter-examples fall apart because they turn out not to be examples of the relevant sense of potentiality at all.