The Aristotelian Biology of Thomistic Natural Law (2)

Eric Johnston's dissertation is a valuable study of how Aristotelian biology supports Thomas Aquinas's account of the natural law of marriage. As Johnston indicates, his dissertation is primarily a historical work that tries to understand Aquinas's position, without judging whether that position is defensible as being simply true. But still, it's clear that Johnston is generally supportive of what Aquinas says, and he so he wants to defend Aquinas as making intellectually respectable arguments.

Any defense of Aquinas's biological reasoning today requires some judgment as to whether it is compatible with modern biological science, assuming that we agree that that science is generally correct. And, indeed, Johnston does suggest that Aquinas's biology is roughly compatible on many major points with modern biology, although he does this only briefly and often only in some footnotes.

I would go farther in that direction than Johnston wants to go, and that's why I disagree with him on four points.

First, Johnston assumes that biological science can study only the purely physical side of human life, and therefore it cannot account for the mental or moral reality of human experience (11, 48, 52, 240). But this is not true either for Aristotelian biology or for modern Darwinian biology. Aristotle's biological writings study not just the physical but also the mental capacities of animals, and it's this biological study of animal cognition that is so important for Aquinas. Darwin continued in this tradition in studying the evolution of the mental and moral capacities of animals. Today, the ethology and neuroscience of animal cognition belong to this Aristotelian tradition of biological psychology. It is true that human beings are unique in ways that make them uniquely capable of moral judgment and symbolic reasoning. But even these humanly unique traits can be understood as products of the emergent evolution of primate cognition.

Johnston observes: "modern biology, viewing the animal from a purely physical perspective, cannot engage the question of ensoulment because it does not engage the question of the soul" (240). But while it is certainly true that modern biologists are unlikely to use the language of "soul" and "ensoulment," they will talk about the biology of cognition and mental states. So, for example, as indicated in some recent posts, primatologists will look for evidence that chimpanzees have a "theory of mind."

My second disagreement is that, while Johnston does occasionally defend the Aristotelian biology of sex differences against the charge of sexist bias (27, 158-159, 233-234, 241), I would go farther in this direction in arguing that Aristotle's embryological explanation of male-female differences is close to what we know today from modern biology. Aristotle understood that the formation of a male embryo depended on the action of testicular secretions in the womb, and that in the absence of these secretions, the embryo develops as a female. Consequently, abnormalities of hormonal masculinatization can result in abnormalities of gender identity. I have laid out my reasoning on this in an article: "A Sociobiological Defense of Aristotle's Sexual Politics," International Political Science Review, 15 (1994): 389-415. Some of this same ground is covered by an article cited by Johnston: Michael Nolan, "The Aristotelian Background to Aquinas's Denial that 'Woman is a Defective Male,'" The Thomist, 64 (2000): 21-69.

My third disagreement is that, unlike Johnston, I think that the ecclesiastical persecution of those studying Aristotelian natural philosophy might have made it necessary for Aquinas to engage in esoteric writing to avoid persecution. Dante hints at this in the DIVINE COMEDY (PARADISO, X.82-148). Siger de Brabant was condemned as an Averroist heretic who taught Aristotelian philosophy without regard for Christian faith. Dante puts him in Heaven, and he has Thomas Aquinas praise him as one who "demonstrated truths that earned him envy." Aquinas introduces himself as "a lamb among the holy flock that Dominic leads on the path where one may fatten well if one does not stray off," thus suggesting that Aquinas hid his support for Siger so as not to stray too openly from the faith of the Dominicans.

One place where Johnston might have seen this is in Aquinas's use of embryology to answer the question (in De Potentia, q. 3, a. 9) of whether the rational soul can be transmitted through semen, or whether it must be infused by God's miraculous creation. Johnston notices that this requires an unusually complicated response by Aquinas (241-59). Aquinas indicates that this question of whether natural embryological development can produce the rational soul of a human being "has been answered in various ways by different people" with different "opinions." One of these "opinions" was that yes, indeed, natural reproduction could produce a child with a rational soul. But then the Church condemned such "opinions" and declared that the rational soul must be specially created by God and then infused into the body of the developing child. "Now to maintain that the soul is made by the generation of the body, is to say that it is not subsistent and consequently that it ceases with the body." This is a heresy, and it was one of the propositions condemned by the Bishop of Paris in 1277. Thus, Aquinas could not openly embrace this without being condemned as a heretic (cf. ST, I, q. 118, a. 2). Aquinas argues in defense of the Church's position--that the rational soul must be specially created by God and infused into the body--but he refers to this as an "opinion," which might make a careful reader wonder whether he is fully and honestly affirming its truth.  For Aquinas, "opinion"--as opposed to "science" or "faith"--is affirming something without firm confidence (ST, I-II, q. 67, a. 3).

Aquinas's argument for this "opinion" is that nature is an instrument in the hand of God, and therefore God can intervene at any time to go beyond what the instrument can do on its own. But if God is able and willing to use nature to create nutritive and sensitive souls, as Aquinas says, then why is He not able and willing to use nature to create rational souls? Although a reader might raise this question, Aquinas cannot openly raise it himself without risking persecution.

This is still an issue today with regard to how far the Catholic Church can go in accepting modern evolutionary science. In 1996, Pope John Paul II appeared to endorse the idea of human evolution by purely natural processes. But he also insisted that while evolutionary science can explain the natural evolution of the human body, the appearance of the rational soul unique to human beings requires a miraculous act of God in the embryological process.

My final point of disagreement with Johnston is in his observation: "His account of the natural law is thoroughly theonomic. Natural law is not a way of discerning the good life in abstraction from God" (296). I agree that any orthodox Christian must believe that all of nature, including natural law, is ultimately part of eternal law as created by God. But it does not follow from this that the power of natural law depends on a belief that it is divinely ordained. If that were so, then there would be no reason for Aquinas to distinguish between natural law and divine law, and thus natural law could not be comprehensible as purely natural without supernatural revelation. If natural law corresponds to the natural biological inclinations of the human animal, then why doesn't the natural power of those inclinations hold true for us regardless of our religious beliefs?

To go back to the example of marriage, all human beings should be able to grasp the natural truth that human beings as sexual animals are naturally directed to parental care and spousal love. And while belief in some theological view of marriage might reinforce those natural inclinations, the natural inclinations can stand on their own natural ground even without religious belief. By contrast, the religious view of marriage as a sacrament symbolizing the marriage of Christ and His Church depends upon faith in revelation rather than reasoning about nature.

In addition to my recent posts, some of my older posts on related topics can be found here, here, here, here., and here.