In a recent online essay for the New York Times, the eminent English philosopher Sir Roger Scruton rightly argues that human persons are not reducible to material forces, correctly insisting that we are aware of ourselves and others as subjects of moral responsibility, of free choice, and of rationality. However, he also says: “philosophers and theologians in the Christian tradition have regarded human beings as distinguished from the other animals by the presence within them of a divine spark,” which they call the soul, and that “recent advances in genetics, neuroscience and evolutionary psychology have all but killed off that idea.”
We agree that human beings are both animals and persons, but it is important that the Christian (and Jewish, and Muslim, and classical) description of the soul not be reduced to a caricature. Indeed, properly understood, the traditional philosophical and theological concept of the soul is indispensable in integrating what the empirical sciences reveal about the world and ourselves with what we know about ourselves as rational and moral beings.
The claim that genetics has helped “kill off” the idea of the soul usually rests on the notion that the actions of DNA molecules are sufficient to explain the events occurring in the larger-level entities of which they are parts—namely, the organisms, human beings included. The idea is that the characteristics of organisms are sufficiently explained by the properties of and the spatial relations among their microphysical components. And so (on this view) there is no need to appeal to the causal powers of the organism as a whole to account for what occurs in it. Therefore, genetics could assist in a general program to explain away higher-level properties such as nutrition, growth, perception, and thought, by reference to the properties of the microphysical components.
However, while bold promissory notes to provide such explanations have been given, actual payment—in the form of adequate explanations—has never been provided. Moreover, if such a reduction could succeed, whole animals could not then actually be single entities—“composite substances,” to borrow Aristotelian language—but mere aggregates of microphysical entities. This reduction wouldn’t just negate the idea of a soul but also the idea that we are both animals and persons.
Of course, many complex objects are mere aggregates. Many of the things we might view as unitary objects actually only produce effects that can be fully explained by the properties and interrelations of their constituents. For example, as Trenton Merricks points out in his Objects and Persons, what a baseball does can be fully explained by the concerted actions of its constituents. A baseball shatters a window, not in virtue of any property of the baseball as a whole, but in virtue of the properties and spatial relations of microphysical entities it contains. However, other composite objects, particularly organisms, have causal powers belonging to the complex substance as a whole. When a human being walks to the refrigerator to retrieve food for a meal, this is a behavior performed by the organism in virtue of conscious properties—properties that belong to the complex substance as a whole. She walks to the kitchen and not to the living room because of her memory and belief that that’s where the food is. Such a conscious belief can scarcely be conceived of as inhering in this or that particle, or as a structural relation of the particles to each other. Rather, it inheres in the organism as a whole and guides the behavior of that organism as a whole. Thus, the unity and causal properties of the organism as a whole are irreducible to the powers and relations of the microphysical entities it contains as parts.
Nor has neuroscience helped “all but kill off” the concept of a soul. It could do so only if it showed how thought could be reduced to neuro-processes. But many have pointed out the insuperable difficulties for such a reduction. Any argument advanced to support such a feat would logically undermine itself. For the point of the reduction would be to show that one’s thoughts are fully explained by the interactions of electrochemical processes operating according to physical, not necessarily logical, laws. But if one’s thought—including the reductionist’s argument itself—rests on such non-rational causes, it is undermined, since beliefs that are determined by non-rational causes, rather than reasons, are thereby made suspect. If my thoughts are merely the result of the electrochemical processes in my brain, then they are non-rational.
Of course, a proponent of the reduction might object that there can be more than one explanation for an event, and so the thought’s explanation on one level (neurons firing) does not preclude its simultaneous explanation on another level as well (logic). And thus, he might say, thoughts are identical with or fully determined by brain processes, but these processes can be explained in both physical and logical terms. Just as the same material event can be explained both by biology and by physics, and the two explanations are compatible, so here (it might be argued), one can give both an explanation by reference to logical laws and by reference to brain processes and their wholly materially determined interactions.
The proposed reduction of thought to neurochemical processes could succeed, however, only if the actions of the neural components, operating according to physical laws, determine the reasoning processes—that is, determine which conclusions one draws in an argument. On a reductive view of mental events, the premises (or the acts of accepting the premises) have the causal powers they do only in virtue of their physical properties, and so the logical laws—the relations among contents of thought just as such—will be utterly irrelevant. Thus, if thoughts are just neuro-processes, governed by physical laws, then the laws of logic are dispensable, and the physical antecedents of a thought (such as a conclusion) determine it regardless of the contents of those antecedents. But this renders the argument by which one defends the attempted reduction unworthy of acceptance. Thus, thought cannot be adequately explained by neuroscience alone.
Thus, some properties and causal powers of organisms belong to them as wholes rather than merely resulting from the sum of the properties and causal powers of their components, and so organisms are substantial entities rather than mere aggregates. But as complex substances, each organism must have a principle of unity making its components a single whole. This principle cannot itself be a concrete component; the resulting unity would not be a single substantial entity composed of parts, but one entity acting on others—an accidental whole, a mere aggregate. Nor can the source of unity be merely a relation accruing to those components, which remain what they are but acquire ordered relations to others. What is required is a factor that unifies the materials in order to make them one being, one substance, and makes the parts be what they are because of their place within that whole. It must be a principle of organization that is logically prior to and not merely the result of the causal properties of the parts. Such a principle is precisely what the Aristotelian tradition called a “substantial form.” In a living being, such a form is a soul.
The role of such a principle can also be understood as follows. Animal organisms die, and some are consumed by other animals. It is obvious that some of the matter-energy that once went into the make-up of one animal ends up in the make-up of another. In fact, all of the materials, or matter-energy, within an animal could end up in the make-up of another. And so within the animal now there must be a formal principle, a principle of unity, determining the matter-energy in its make-up to be of this kind rather than of another kind. This is the substantial form. In a living being, it is called a soul.
One can of course rightly affirm many things without affirming the existence of a soul, but some of these affirmations cannot be made sense of without affirming a soul. One can agree that human beings are both animals and persons without first appealing to the notion of the soul—and one could even be derisive of that concept at the same time. But one can give no intelligible account of those affirmations of our nature as personal animals without the concept of a soul—as that term has traditionally been used and understood.
Moreover, while organisms are irreducible to the laws and properties of the chemicals and particles composing them, likewise the human person (as Sir Roger rightly suggests) is irreducible to the laws and properties of organisms. Human thoughts and choices cannot be fully explained by biological laws and properties: the dimensions of logic and morality are distinct and irreducible types of reality.
Still, the source of thought and choice in a human person cannot be a distinct agent or a substance distinct from the human organism. It must be the same agent that believes the food is in the kitchen (a person or thinker) and that walks there (an organism). So, on the one hand, the human thinker and the human body are not two different things, but one complex substance with different powers. On the other hand, the human person engages in operations—thought and choices, for example—that are not reducible without remainder to the laws and properties of natural, material entities.
If one denies the first point, one will view the bodily aspect of the human person as a mere extrinsic instrument, without inherent meaning and importance. If one denies the second point, one fails to acknowledge the human being precisely as a person, as a source of uniqueness and originality and the bearer of rights. But to make sense of the compatibility of both points one needs the concept of a substantial form—soul. Without that, the organic aspect of the person will lack substantial unity and either the distinctiveness of the person will be denied (reverting to materialism), or the person will be viewed as separate from the organism (“ghost in a machine”).
We are directly aware that we persist through time and that our plans, deliberations, and choices extend through time. Such activities cannot be attributed to this or that material component, or to a group of components in a mere accidental whole. So if the organism is viewed as a mere aggregate, a mere mass of particles, the personal subject will inevitably be viewed as a separate agent making use of that mass of particles as a mere extrinsic tool. Without the idea of a human substantial form or soul one cannot intelligibly relate the organic to the personal, the world of the “life-form” to the world of the empirical sciences.
Patrick Lee is Professor of Philosophy and John N. and Jamie D. McAleer Professor of Bioethics at the Franciscan University of Steubenville. Robert P. George is McCormick Professor of Jurisprudence at Princeton University. They are the authors of Body-Self Dualism in Contemporary Ethics and Politics (Cambridge University Press.)