In yesterday’s article, I argued that philosophers who defend abortion often misunderstand the pro-life argument’s appeal to potentiality by thinking that it refers to possible future states of affairs. Today I want to explain and correct that misunderstanding by explaining developmental potentiality according to the substance view of persons.
The substance view of persons holds that every human being either has the potential to manifest any and all properties essential to personhood or does actually manifest them. For the adherent of the substance view of persons, "potential" does not essentially refer to some possible future state of affairs. Rather, in this conception of what I will call developmental potential, to say that an organism has the potential to manifest some property means that that property belongs essentially to the kind of thing that it is (i.e., is among the essential properties it has by nature). Whether or not a specific individual actualizes the potentialities of its nature is contingent; but those potentialities necessarily belong to its nature in virtue of its membership in a specific natural kind.
The contingent failure of an individual to actualize an essential potentiality does not affect the essence or nature of that individual. For example, by nature human beings are bipedal, but of course human beings have been born without legs. However, a congenitally legless man is as much a human being as anybody else, though he is literally de-formed or de-fective. Indeed, it is important to realize that defects conceptually depend on some standard of normality (much as the exception proves the rule). To say of something that it is defective means that it is defective with respect to some good or perfection. To say that an organism is defective means that it is defective with respect to the perfection of its nature.
So it is only because the congenitally legless man lacks a normal human property that he is a "defective" (literally, "mis-made") human being. But it’s very important to see that a defective human being is as much a human being as any other individual. Indeed, we all contingently fail to manifest various human perfections, both physical and moral, so barring one possible exception, all human beings that have ever lived are defective in some sense.
Ultimately, to understand the difference between these two senses of potential, we need to recognize the difference between organic development and substantial change. Development presupposes substantial identity over time. For something to develop, the same thing must exist before and after the development. To use a famously misunderstood example, acorns develop into oak trees because once the acorn begins the oak tree life cycle, the same organism grows through a series of immature stages (e.g. sprout, sapling, etc.) before actualizing the potentialities characteristic of a mature oak tree. Judith Jarvis Thomson famously offered the dismissive remark that a “newly fertilized ovum, a newly implanted clump of cells, is no more a person than an acorn is an oak tree.” But, of course this is a confusion: an acorn is an immature stage in the life cycle of a single oak organism and a zygote is an immature stage in the life cycle of a single human organism. (The fact that we tend to use the same phrase ‘oak tree’ to refer both to the natural kind as a whole and to the mature stage of that natural kind can lead to confusion.) To say that an acorn is not an oak tree is just as true, and just as banal, as saying that an infant human being isn’t an adult human being. Whether the infant is a person, however, is an entirely different matter.
Of course sometimes changes can occur that are so radical that there is no substantial identity across time—instead something is destroyed and a new thing comes into existence. When such changes occur we do not generally speak of development. So, for instance, we would never normally say that the oak tree developed into a dining room table. Once the oak tree was cut down it ceased to be a living organism and so the substantial unity of its life cycle was ended. The oak plant ceases to be, and the matter that once constituted the oak tree organism becomes the matter of an artifact through the industry of human hands. When this occurs, however, there is a new entity—the dining room table—that in no way developed out of the oak tree; instead it was constructed out of matter that previously partially constituted that tree.
David Oderberg has another helpful analogy that illustrates this difference between developmental potential and the sense of potential as a possible future state of affairs. Oderberg notes that there is some sense in which the butter, eggs, flour, and sugar in my kitchen might potentially become a cake. But nobody would normally say that there is a potential cake in my kitchen right now in virtue of its containing those ingredients. Nor would anyone normally say that those ingredients have the potential to develop into a cake the way that the acorn has the potential to develop into the oak tree. Developmental potential embraces some kind of potentiality intrinsic to the nature of a natural kind, while the other sense of potentiality as future possibility is basically extrinsic to any kind of nature.
To return to the human case, the substance view of persons claims the substantial identity of a zygote with all of its later "selves" as developments of the same underlying thing, though not with its material precursors (i.e., its parental gametes). I began my existence as a zygote. I am just as much the same thing as that zygote as I am the same thing as my one-year-old self. This is important because the ground of my identity with my one-year-old self cannot be either material or psychological. I do not share the same matter as that child, nor do I share any memories or experiences with him. And yet surely I am the same human being, the same organism, the same substance, the same person. I am a development of that child, and those many years ago that child, and that child alone, possessed the potential to develop into the man that I now am.
What follows from this is that my capacities for rationality (such as they are) must have been in some sense latent in that child. Because the same person persisted across the development, that potential was a developmental potential. We can ask why that child possessed that potential, but a kitten or a spider does not. The answer is obvious. That child possessed a human nature, and the capacity for rational thought is an essential property of human nature. Suppose that something had happened to that child (e.g., it had been killed in a traffic accident) so it had never developed into an individual that manifested rationality. Would that mean that it was not a person? Of course not. Contingent future states of affairs do not determine what something essentially is.
If it is true that I am identical with my one-year-old self, then that is just as true of my newborn self, my late fetus self, my embryo self, my blastocyst self, and my zygote self. If there is substantial identity among all of those different time slices of my life, then all the later time slices are developments of the earlier ones. What that means is that anything that is essentially true (i.e., true by nature) of any of those time slices is true of all of them. Therefore, if I am essentially a rational being (now), then my one-year self, my newborn self, my zygote self, and so on were the same rational being.
In this view, my existence began as a zygote, as an independent organism with a full human nature that persists to this time. Of course I had material precursors—my parents' gametes. However, the zygote that those gametes contributed their matter to form was an entirely new entity, a substance different from theirs. I inherited some material from my parents' gametes, but those gametes ceased to exist (as substances in their own right) once I was formed (similar to how my lunch ceased to exist as it was metabolized by my body). At my conception a new entity existed in the universe, a new substance of a rational nature, a new person.
If (per impossibile) some magic injection could turn a kitten into a person, that would be a similar kind of substantial change. Just as my parents' gametes were substantially destroyed by my conception, if Michael Tooley's magic injection (referenced in yesterday's essay) were possible it too would bring about a substantial change that destroys the cat nature of the kitten. A new entity—a new substance of a rational nature—would have come into the world. But of course no such injection is possible.
This distinction in the different senses of potential is why the pro-life appeal to potential is not undermined by the abortion defenders' putative counterexample. They deeply misunderstand potential as simply a matter of possible future states of affairs, instead of as a matter of essential properties that have contingently not been actualized. Now we can restate the argument from yesterday in a way that makes this distinction clear so that it is unaffected by the putative objection:
(P4') Anything with the developmental potential to manifest P is (always already) a moral person.
(P5') Very young human beings have the developmental potential to manifest P.
(P6') Therefore, very young human beings are (always already) moral persons.
No kittens or spiders can falsify (P4') because no kitten or spider has the developmental potential to become a person. If there is any sense at all in saying that they have the potential to become persons, it is solely because (in the world of Tooley’s magic injection) they have the potential to be material precursors to an ontologically new entity, just as one might say that a sperm and ovum have the potential to be material precursors to a zygote.
Of course this substance view of persons depends on an essentialist metaphysics that I have not really defended here. On the other hand, the pro-abortion position implicitly depends on a reductive materialism that is also undefended. This comes out especially in the way that both Tooley, and David Boonin, insist on talking about brains and seem to assume that having a "big enough brain" is all that is required to "function as a person" (apparently forgetting about whales). There are more reasons to accept the substance view of persons that I can explore here, but they all basically come down to the fact that the substance view does a much better job of picking out the right cases than the alternative. Unlike many of the other views, the substance view correctly identifies infants and the comatose as persons.
To return to my initial theme from yesterday, I think that anybody with a bit of common sense can see that zygotes develop into individuals that manifest rationality and kittens and spiders do not. While this common sense view can be backed up by a sophisticated hylomorphic metaphysics, it really shouldn’t be necessary. I often think that only a professional philosopher could be so obtuse as to think that there is something strange about it.
Mathew Lu is assistant professor of philosophy at the University of St. Thomas.