In my last brief, I summarized the chilling argument  from the 2012 Journal of Medical Ethics (JME) defending the indefensible practice of killing infants after birth (so called “after birth abortion”). I described how the authors argue that neither fetuses nor newborns are persons and therefore can be treated in a subpersonal way (killed). And I noted that the May 2013 issue  of the JME continues the appalling conversation over the legitimacy of infanticide.
I proceeded to introduce an argument  of Michael Tooley’s against fetal and infant personhood found in the May 2013 issue. Tooley argues that since the concept of an immaterial soul is unsound, any argument against killing fetuses and infants that depends on the existence of such a soul is also unsound.
In reply, I pointed out that Tooley paints all defenders of the rational soul in the image of René Descartes’ “substance dualism” and then dismisses the concept of the soul as obviously unsound. I said that although Cartesian dualism is indeed unsound, Thomas Aquinas’ account of the nature of the relationship of body and soul is rationally persuasive and not at all threatened by Tooley’s simplistic caricature.
In this essay I set forth Aquinas’s account of why the rational soul must be immaterial. The argument is complex and Aquinas’ terminology can be difficult to navigate. I therefore attempt to translate his argument into language more consistent with contemporary idiom. Even still, the argument is rough-going. Nevertheless, I think it will repay a careful consideration.
Aquinas’s argument for the immateriality of the rational soul proposes no mystifications about ghostly essences floating inside mechanical bodies; nor does it argue that any human act is anything other than the act of an embodied person. It argues only that a certain kind of act that we indisputably carry out—concept formation—cannot be sufficiently accounted for by the acts of any material organ. And so it concludes—as Aristotle, who was not a Christian, also concluded—that the rational soul must not be anything material.
Aquinas’s argument can be summarized in nine steps:
1. Human knowing includes the knowing not only of particular entities (this furry orange thing)—called sensory knowing, but also the knowing of kinds (cat)—or intellectual knowing. In other words, we not only have the ability to perceive individual things, but also to know them as particular examples of an abstract kind.
2. The act by which we know a thing’s kind is the act of forming universalized concepts. We first perceive actual things, say, cats or images of cats; over time we abstract from those perceptions the universalized concept of “cat”. We then apply the concept to concrete instances and so come to know the abstract in the individual: “my furry orange cat Jack.”
3. Now individual things can only be perceived as individual because they are constituted of matter. It is precisely their material existence that makes them perceptible. Abstracted from their sensible qualities, they are not objects of perception.
4. In a related way, a universalized concept is universal precisely because it is abstracted from individuated things.
5. The brain is the organ that knows individual things. It knows them because it receives into itself, encodes and manipulates information pertaining to their sensible features (their color, shape, texture, extension, odor, sound, flavor, temperature, surrounding context, etc.).
6. The act of receiving information pertaining to a thing’s sensible features must be an act of an individuated (i.e., materially instantiated) power; that power is the brain.
7. When we form universalized concepts, we receive information abstracted from everything sensible and individual. Universalized concepts are contents of thought that contain information free from all the sensible manifestations of material things (free from every spatio-temporal representation). As universalized, they are empty of sensible content. Thus, in concept formation the intellect must take the sensible image and somehow strip it of its sensible data, of the concrete conditions of materiality in which it is cloaked in our sensory perceptions. Through concept formation we move from the perceptual knowledge of sensible reality to an intellectual understanding of things. But if there is nothing sensible to receive in a universalized concept—no color, texture, odor, flavor, temperature, historical context, etc.—then there is no data of particularity for the brain to encode. Yet universalized concepts are not empty realities; they are data-rich. But—and this is the central point—the data of a universalized concept, as not pertaining to anything individual, is not encodable, retrievable or expressible in the form of a cognitive representation.
8. If universalized concepts contain nothing pertaining to sense data, there is nothing for the brain to transmit. It follows that the formation of universalized concepts are not acts of the brain (not bodily acts). If they are not bodily (material) acts, but they pertain to the person, they must be acts of some non-bodily (immaterial) part of the person.
9. We call that immaterial part the rational soul.
Some might still question whether Aquinas’s account replies adequately to Tooley’s main objection. Recall from Part I of this essay that Tooley believes that if we had an immaterial soul (mind), then injury to the brain, including degenerative diseases, would not affect our mind and hence our process of thinking. But this is not what we find. We find that the precise region and extent of human brain injuries correspond to commensurate types and degrees of cognitive impairment. So scientific investigation rules out the plausibility of the hypothesis of an immaterial soul.
But recall, Aquinas is no Cartesian. The soul (mind) does not float around independent of the body having activities of its own unrelated to the body. It is true that abstract reasoning is not reducible to brain activity. But saying this emphatically does not mean it is not carried out in conjunction with the brain. Since intellection entails abstracting universalized concepts from particular sensible images, it necessarily involves interaction with brain structures responsible for sensory cognition, especially structures that encode, preserve and retrieve sensible images.
Neuroscientific literature reports that acts of abstract reasoning cause predictable activity in the brain’s neocortex. The empirical data therefore justifies no more than the Thomistic conclusion that concept formation is carried out in conjunction with precise systems of the brain’s neocortex. It does not justify the materialist conclusion that abstract reasoning is reducible to brain activity.
Since as we have seen there is good reason for concluding that the material structures of the brain are inapt for encoding, retrieving and manipulating universalized concepts, we are justified in concluding that the scientific data only partially accounts for higher acts of human cognition. It accounts for the encoding, preserving and retrieval of the sensible images employed by the immaterial soul in concept formation.
But it does not account for the knowing and manipulating of abstract ideas. For this an immaterial power is required. We call that power the rational soul.