Most closely associated with the teachings of Aristotle and Thomas Aquinas, anthropological hylomorphism is one view of the relationship between body and soul.
Hylomorphism is the theory that “matter” (pure, abstract essence) combines with “form” (that which gives something its nature) to make “substance” (what we usually consider matter). For example, unformed clay can be shaped and hardened to make a brick—the clay is the “matter,” and the shape and hardness are the “form”; the brick is the resulting “substance.”
Anthropological hylomorphism applies this theory to the nature of man. How are the body, soul, and spirit related to each other? Most Christian discussions of this issue revolve around the trichotomy vs. dichotomy debate. Both views indicate some separation between soul and body. Aristotle, Aquinas and others held that the body is “matter” and the soul is the “form” which gives a person his nature. They also believed that form and matter are inextricably combined and dependent on one another. A brick cannot be a brick without the combination of clay and hardness and a particular shape. In the same way, a human cannot be a human without the combination of body and soul.
The term anthropological hylomorphism itself means “matter” (hylos,) and “form” (morphos) of “man” (anthropos). Aristotle borrowed these terms from Plato, whose views on the subject were illustrated in his parable of the cave in The Republic. Aristotle taught that no matter can exist without complying to a form, and no form can exist without having a presence in matter. Thus, Aristotle taught that the body cannot live without the soul, and the soul cannot live without the body (there can be no afterlife).
Aquinas was not so emphatic about form and matter’s inseparability. As a Dominican priest, Aquinas had high regard for Scripture, which indicates a separation is possible. Verses such as Matthew 10:28 teach that the body and soul are not mutually dependent: “Do not be afraid of those who kill the body but cannot kill the soul.” Perhaps the strongest argument against stringent Aristotelian hylomorphism is in 1 Corinthians 15:40, where Paul writes of the resurrection: “There are also heavenly bodies and there are earthly bodies; but the splendor of the heavenly bodies is one kind, and the splendor of the earthly bodies is another.”
Nevertheless, Aquinas was able to combine hylomorphism with essential Christian tenets. He claimed that, even though the soul and body are linked, the soul can survive without the body. The soul is simply incomplete until re-embodied. The soul or “form” of a human exists in an unnatural state until God resurrects the body. In this way Aquinas explained the transition between the death of the earthly body and the resurrection of a heavenly body. Having a body, according to Aquinas, is essential to being human, and thus humanity cannot be perfected without one.