Thomistic vs. Cartesian Substance Dualism

In chapter 6 of Body & Soul: Human Nature & the Crisis in Ethics, entitled “Substance Dualism & the Body: Heredity, DNA & The Soul, Authors J.P. Moreland and Scott B. Rae introduce the chapter by focusing on the distinctions between Cartesian and Thomistic substance dualism. While René Descartes’s and Thomas Aquinas’s views of Substance Dualism agree on the vast majority of points, two key differences exist between them. First, Descartes reduced the soul to the mind thus identifying the person as “a purely conscious substance or at least a substance with the ultimate capacities for consciousness.” In contrast, Aquinas believed that “the soul is broader than the capacities for consciousness and is responsible for the organic functioning and the activities of life.”

Secondly, modern Cartesian substance dualism holds to the notion “that the sole relationship between the mind and the body is an external, causal relationship,” that is the mind is a substance that “is externally related to an ordered aggregate, the body.” In the Thomistic view, however, “a modal distinction [exists] between soul and body: the soul could exist without the body but not vice versa.”

Moreland and Rae then go on to clarify and defend Thomistic Dualism, particularly, using a term coined by Brian C. Goodwin, the organocentric view stating “the organism as a whole (not DNA, which actually presupposes the organism as a unity before it can function) is the fundamental unit of control and information.” Evidence given to support the organocentric view includes the fact that DNA cannot function without the cell itself. DNA does not produce the cell. It serves as a “template for protein synthesis” and gets “copied in the process of cell division.” Nuclear transplant experimentation reveals that a frog zygote with its DNA removed completely or replaced with DNA from a hybridizable species will continue to develop as a frog until it runs out of building material and then die. The end result is the same, a dead embryo of the same kind from which the zygote was taken. The organism develops based on organism type rather than on DNA type. This evidence strongly supports the organocentric view of substance dualism.

Through metaphysics we seek to understand the nature of existence. Therefore the great test of any metaphysical assertion lies in its ability to stand up to the rigors of both real life and the revealed truth of Christian Scripture. This is why I find the organocentric view of Substance Dualism so fascinating. The existence of the specified and complex information found in the DNA molecule provides compelling evidence for the existence of an intelligent designer. My previous understanding was that DNA actually performed the function of director for the development of the body, that the body developed simply upon the basis of biological chemistry and that the soul merely inhabited this physical shell, as it were. I had unwittingly opened the door to the Cartesian molecular-machine understanding of the human body. And this in turn would actually undermine a Christian Theistic worldview of humanity.

I still believe that the complex information in DNA is compelling evidence for an intelligent designer. In addition, I now know the unique position the soul plays in acting as the director of the development of the body placing DNA in its rightful function as a tool, utilized by the soul, to grow a body suitable for expressing its capacities. DNA doesn’t contain the Imago Dei, the person does. A person is not a body only, nor is he a soul simply inhabiting a body like a hermit crab living in any shell it finds. A person is a soul/body unity, as Substance Dualism holds. Thomistic Substance Dualism with its organocentric view of the soul/body relationship, in that order, stands up nicely to the “real-life” test.