Disputes about metaphysical issues rarely make the newspapers. The ancient argument about the nature and identity of the human person, however, turns out to be highly relevant to issues that contemporary Americans read about, and argue about, every day. As Yale psychology professor Paul Bloom recently observed in an op-ed piece in the New York Times , “What people think about . . . gay marriage, stem-cell research, and the role of religion in public life . . . is intimately related to their views on human nature.”

Consider, for example, the abortion issue. Many defenders of abortion implicitly suppose that a human person is a consciousness or series of conscious acts that has or inhabits a body, and so they hold that your human organism came to be at one time but that you came to be at another time (say, with the emergence of your self-consciousness). But if they are wrong, if instead a human person is a human physical organism, then the person came to be whenever this physical organism came to be. Similarly, if the human person is a bodily entity, then it makes no sense to regard the body as a mere extrinsic tool which we may legitimately use simply for the sake of obtaining desirable effects in our consciousness (which is regarded by people who accept dualism as the ” person that inhabits, or is somehow “associated with,” the body)”a view widely held by defenders of sexual liberalism and same-sex “marriage” in particular.

And yet it is often the proponents of traditional morality who are accused of holding a body-self dualism. For example, advocates of abortion often assume that defenders of prenatal human life maintain their position on purely religious grounds, believing on faith that the soul is present from conception onward. Abortion advocates then say that “souls” cannot be shown to exist, assert that this is backed up by science, and then smugly conclude that science is on their side against religious zealots who believe in an unprovable and mysterious soul.

In fact, intelligent pro-lifers do not first inquire whether the soul is present and from that inquiry conclude that there is or is not a human being present. Rather, they understand that it makes more sense to begin by asking whether there are characteristics”physical characteristics”which indicate the presence of a human being, however small and developmentally immature he or she is; it is on the basis of the answer to that question that one can conclude that the human soul must be present. It is actually defenders of abortion who often implicitly assume body-self dualism, even though at other times in the debate they deny or disparage the idea of a soul and embrace or postulate materialism. We will show below that neither body-self dualism nor materialism is sound, that a third possibility represents an intellectually superior view of what a human person is, and that this view is key for understanding many of the great ethical controversies of the day.

An almost pure case of the oscillation between dualism and materialism occurs in Paul Bloom’s op-ed piece. Professor Bloom begins his article by rightly noting that dualism is both widespread and mistaken. He then further states correctly that the question of when human life begins is colored by one’s view of what a human being is. This, he says, is why people often appeal to science to answer the question, “When does human life begin?” But this question, Bloom contends, is not really about life in the biological sense, but about “the magical moment at which a cluster of cells becomes more than a mere physical thing. It is a question about the soul.” Bloom then says that science cannot answer that question because science has in fact demonstrated that qualities of mental life we associate with souls are purely corporeal; they emerge from biochemical processes in the brain.” According to Bloom, “This is starkly demonstrated in cases in which damage to the brain wipes out capacities as central to our humanity as memory, self-control, and decision-making.”

But here Bloom is gravely mistaken. First, his “stark demonstration” is no demonstration at all; it rests on what is manifestly a non sequitur. Shutting off action X prevents action Y: this shows either that X is identical with Y, or that, though X and Y are distinct, Y depends on X to occur. Severe brain damage prevents conceptual thought and decision-making”this much the medieval Christian philosopher and theologian Thomas Aquinas recognized centuries ago, and Aristotle centuries before that. But their view was that conceptual thought and decision-making in human beings depends on brain operations (to provide sense experience), even though (for different reasons) they also held that conceptual thought and free choice are distinct and nonbodily operations. Thus, Bloom has presented no compelling argument at all for his materialism or for the “great conflict between science and religion” that he claims to exist on the question of human nature.

Second, pace Bloom, if science did show that all human acts, including conceptual thought and free choice, are just brain processes, then science would provide answers to important moral questions. It would just provide answers different from those we have traditionally accepted. In particular, it would mean that the difference between human beings and other animals is only superficial”a difference of degree rather than a difference in kind; it would mean that human beings lack any special dignity worthy of special respect. Thus, it would undermine the norms that forbid killing and eating human beings as we kill and eat chickens, or enslaving them and treating them as beasts of burden as we do horses or oxen.

In fact, however, the empirical sciences themselves have nothing to say one way or the other about whether there is an aspect of human beings”such as the source of conceptual thought and free choice”that is not simply a material process or a by-product of material processes. And given the limitations of their methods, the empirical sciences have nothing directly to say about an intrinsic human dignity and what the basis of that intrinsic dignity might be. So there is no “great conflict” between religion and science with respect to psychology; this “conflict” is a fiction invented by scientists unwarily wandering into the domain of philosophy. Of course, there are philosophers who defend materialism and who argue intelligently with their fellow philosophers who reject it; but the argument by which Bloom purports to demonstrate materialism is worthless.

Bloom’s reasoning here exemplifies a common confusion. Defenders of abortion and euthanasia often oscillate between body-self dualism and unscientific materialism, depending on which one will further a given line of argument. For example, faced with evidence showing that the life of a human individual begins at conception, they deny that embryonic humans are persons or selves, implicitly identifying “persons” with consciousnesses. But, later in the debate, accused of drawing the line between persons and nonpersons in an arbitrary way, they then claim that such line-drawing must be arbitrary since we are all just aggregates or concatenations of material particles. One moment they claim that we are consciousnesses that use our bodies; the next moment they say we are purely material, different only in degree from other material entities.

Bloom contends that because science has established materialism, it is therefore unable to answer the question, “When does human life begin?” But the premise is untrue and the argument invalid. Science does not establish materialism, and even if it did, this would not preclude it from answering the question of when human life begins. Actually, the opposite of this argument is closer to the truth: if body-self dualism were true, then science could not answer that question. Bloom’s mistake here is the common one of supposing that the idea that life begins at conception (in a way that can settle debates over abortion and embryo-destructive experimentation) is somehow tied to the idea that there must be a “magical moment” when a soulless body becomes ensouled: “There is no moment at which a soulless body becomes an ensouled one and so scientific research cannot provide objective answers to the questions that matter most to us” (emphasis added). This is confused. It is true that (empirical) science cannot by itself settle the whole ethical issue concerning the moral worth of embryonic and fetal human life. But if it is true that every distinct, human individual has intrinsic dignity (a proposition that most Americans hold, and one for which we have offered philosophical arguments in other writings), then science, and in particular embryology, can answer an important question”namely, when does a distinct human individual come to be?

And the answer provided unanimously by the leading texts in embryology is quite clear. As one text puts it: “Human development begins at fertilization when a male gamete or sperm (spermatozoon) unites with a female gamete or oocyte (ovum) to form a single cell”a zygote. This highly specialized, totipotent cell marked the beginning of each of us as a unique individual” (Keith L. Moore and T. V. N. Persaud, The Developing Human: Clinically Oriented Embryology , 5th edition; see also William J. Larsen, Essentials of Human Embryology ; Scott F. Gilbert, Developmental Biology , 7th edition; and Ronan O’Rahilly and Fabiola Muller, Human Embryology and Teratology , 3rd edition).

Ironically, Bloom (like many others) seems to be misled on this by an implicit consciousness-body dualism. He evidently holds that nothing is intrinsically valuable (as a subject of rights) without a functioning mind. And because he supposes that science has shown that the mind is material and develops gradually, having emerged more generally by evolution, he concludes that it cannot be determined with certainty and precision when this intrinsically valuable entity is present and when it isn’t.

However, contrary to this view, what is intrinsically valuable is not the mental functions or qualities we have, but the being, the substantial entity, that you and I are. (By “substantial entity” we mean the thing that one is rather than the characteristics or properties one possesses.) You and I are intrinsically valuable and equal in fundamental worth and dignity because of what we are, not because of qualities we may (if all goes well) acquire at some point during our lives”qualities that come and go, and which some human beings possess in greater degree than others. And so we are intrinsically valuable in a way that makes us possessors of dignity and bearers of rights from the point at which we come to be, and we remain possessors of dignity and bearers of rights until we die.

Since dualism is mistaken”since we are not consciousnesses inhabiting bodies but are physical organisms possessing from the beginning a human (i.e., rational) nature”it follows that we came to be when these physical organisms came to be. And the science of embryology does determine when that occurs”namely, conception. Bloom uses materialism to rule out the possibility that one could draw the line between persons (beings with full moral worth) and mere things in an objective and nonarbitrary way; but he implicitly adopts the very body-self dualism he criticizes when he assumes that there is something intrinsically valuable in human beings only when actual mental functions or states are present.

Like many others, Bloom seems to have rushed to an acceptance of materialism because he erroneously supposes that if dualism is false then materialism must be true. It is widely assumed that dualism and materialism exhaust the alternatives: either we are souls which possess or inhabit our bodies, or everything in us is completely explainable by matter and material processes. But there is a third possibility, one that avoids the problems associated with dualism and materialism.

On the one hand, a human being is essentially a physical organism, an animal. This point is shown (though the full argument would require more space than we have here) by the fact that you and I”not any entities which we merely possess or inhabit”perform and undergo bodily actions. Sensation and perception are clearly bodily activities: they are performed with bodily organs such as the senses and parts of the brain. So the subject that does the sensing and perceiving is a bodily entity, an animal organism. But it must be the same subject, the same “I,” that senses or perceives and that engages in conceptual thought (though conceptual thought is not itself a bodily action”more on this in a moment). For it must be the same subject that perceives the ink marks on a page, for example, and that understands the intelligible message signified by them.

On the other hand, conceptual thought and free choice cannot be material actions; they must be spiritual or nonmaterial actions. Conceptual thought inevitably refers to a universal feature or aspect of the object of thought (for example, what an animal is, as opposed to this or that particular animal), a feature or aspect not of itself restricted to a particular place or time. But every material action has as its object an entity that is restricted to a particular place and time. Hence there is an aspect of us, a capacity or power, which is nonmaterial. It is nonmaterial in the sense that the actions in it and its existence do not depend on matter”whereas a material aspect of a thing is intrinsically circumscribed by a particular space and a particular time.

But this immaterial aspect is not the whole self, only an aspect or part of the self. On the one hand, then, one can hold that the human being is not a soul alone, but the whole living bodily entity, a composite of body (or matter) and soul (the “form” or organizing principle of the living thing). On the other hand, there is an aspect of the human being that is nonmaterial, and could not have emerged from matter and material forces. So neither body-self dualism nor materialism is correct. We are essentially physical organisms, and so we come to be when these organisms come to be”at conception. Yet we are more than just the latest product of blind evolution, since there is an immaterial aspect of us that could not have emerged from lower material forces.

The third alternative we have outlined here is hardly an invention of ours. In one variant or another, it has been held by many of the most distinguished philosophers in history, and many hold it today. Moreover, it has been accepted by some religious traditions, including the world’s largest religious body, the Catholic Church. The Church rejects both materialism and body-self dualism. The human being is not just a set of material processes; nor is it a consciousness possessing or inhabiting a body. As Aristotle recognized even in antiquity, and as many others have understood since, the human being is a rational animal”an integrated unity of body and soul.

Patrick Lee is Professor of Philosophy at the Franciscan University of Steubenville. Robert P. George is McCormick Professor of Jurisprudence and Director of the James Madison Program in American Ideals and Institutions at Princeton. They are at work on a book on dualism and contemporary ethical questions.

Articles by Patrick Lee & Robert P. George