I’m currently doing some research for a paper on the anthropological implications of Chalcedonian Christology. My working hypothesis is that Christian theology has often insufficiently applied the person-nature distinction (so vital to the church’s Trinitarian and Christological formulae) to the topic of theological anthropology. So, for example, while Chalcedon understands the soul as a part of human nature in which a person subsists (Christ’s human nature consisted of a “rational soul and body”), many Christian theologians continue to articulate an understanding of human personhood that equates “soul” with “person.” On such a Cartesian understanding, the person “just is” the soul. But Chalcedonian Christology seems to demand a distinction between person and soul in order to avoid the error of Apollinarianism. The person of the Son assumed a human nature that was already equipped, so to speak, with a soul, no less than a body. So the person must be distinguished from the soul, at least in the case of Christ. I don’t have space to defend it here, but a strong case can be made that the next ecumenical council, Constantinople II, implies that the same is true for all human persons.
In any event, this Cartesian dualism isn’t the only kind of substance dualism on offer in the Christian tradition. Thomas Aquinas, for instance, articulated a kind of hylomorphic dualism that equated the person neither with the soul nor the body. Instead, on Thomas’ scheme, the soul is the substantial form of the material body that gives to it its rational configuration. The person is the individual thing (suppostium) that exists in and through the soul and the body as constitutive parts of human nature. I have a lot more to read in Thomas (as well as in the secondary literature on him), but the following discussion from the Summa Theologiae (1.75.4) should suffice to demonstrate that Thomas clearly distinguished the person and the soul. In response to the question, “Is the soul man?” Thomas cites Augustine:
On the contrary, Augustine (De Civ. Dei xix, 3) commends Varro as holding “that man is not a mere soul, nor a mere body; but both soul and body.”
Thomas argues that the soul cannot be equated with “man,” conceived of either as a species or as an individual. Instead, Thomas maintains that the soul is a part of man along with the body. He concludes:
Not every particular substance is a hypostasis or a person, but that which has the complete nature of its species. Hence a hand, or a foot, is not called a hypostasis, or a person; nor, likewise, is the soul alone so called, since it is a part of the human species.
So the soul is a substance, distinct from the body, but it is not a subsistence; it is not a person. A person has the “complete nature of its species,” which, in the case of a human being, ordinarily includes (bracketing out the question of the intermediate state) a body and a soul. In sum, Thomas maintains the person-nature distinction even outside of its normal Trinitarian-Christological context and applies it consistently to ordinary human persons as well.