Know Thyself: Part II Body and Soul


In the last installment of this series, we reviewed a central argument for the partial immateriality of human nature. Specifically, we saw how the mind, in particular, must be immaterial given its power to understand the nature of material things without itself becoming those things. This, however, raises a great many questions – one of them being among the most famously disputed anthropological questions in the history of philosophy, namely, the interaction problem. To put it simply, philosophers who claim that at least part of human nature is immaterial must explain how something immaterial can interact with something material (i.e. the body). This was a significant problem for philosophers such as Descartes and Plato, among others. Below I will lay out, in brief, the Catholic case for the unity of body and soul.

Unity of Body and Soul in Catholicism

The Catechism says the soul should be considered the “form of the body.” It also affirms that man is a being “at once corporeal and spiritual.” The Catechism goes on to say, “it is because of its spiritual soul that the body made of matter becomes a living, human body…their union forms a single nature.” These statements have deep roots in the Bible as well as Aristotelian philosophical anthropology. Genesis 2:7 says God fashioned man from dust and breathed life into his nostrils. Herein lies the biblical foundation for the dual yet intrinsically unified aspects of human nature. The dust out of which God fashioned man was lifeless. God intended this life to be the life of the body specifically.

This passage betrays two important aspects of human nature. One part is material (the dust the body is made of). The other part is immaterial (the life given to the body). What’s more, only the union of the two parts constitute human nature. The dust alone and the life alone are not men. The unity of the dust (body) and life (soul) make a complete human being. Therefore, we can properly understand human life only as it is unified with the body. The unity of body and soul also finds support in the Gospels.

Death, Resurrection, and the Soul

Indeed, the Resurrection of Jesus and the general resurrection (Luke 24; John 5: 28-29) are most plausible given this view of the body and soul. If a human being is essentially just an immaterial soul that happens to inhabit a body, then death is not really the end of the human being. Rather, death in this view seems more akin to a driver getting out of a car. No one would say that the driver’s departure from his vehicle entails the end of the driver. If death does not entail the destruction of the human being, the resurrection as well as the punishment of death given to Adam and Eve become mysterious.

Again, if the immaterial soul is what human nature essentially consist of, then death is not something uniquely harmful or disturbing to human nature. This view actually seems to entail that the soul’s union with the body is a hindrance to the human person. This implication is clearly at odds with both the Catechism and the Bible. Therefore, it is only when human nature is understood as an essential unity of body and soul, and not merely as a soul that happens to inhabit a body, that both death and resurrection can coherently bear the significance that they have in Christian theology.

The Unity of Matter and Form

In order to understand human unity better, I think it is necessary to understand the philosophical as well as biblical roots behind this position. Aristotle was the first philosopher to profess the view that the soul is the form of the body. He did this in contradistinction to Plato’s view of the soul which is the view that the soul is the essential component of human nature and the body is merely accidental to who we are, metaphysically, as human beings. Aristotle’s view is called “hylomorphism” which translates from Greek as matter and form.

Aristotle claims that matter and form provide the metaphysical foundation for all things. Human beings are just one particular albeit unique instance of matter and form. On this view, it is a mistake to think of the body and the soul as two separate substances that somehow interact with one another to make a third substance, i.e. a human being. Rather, matter and form are two incomplete substances that come together in order to create one complete substance. On hylomorphism, this is true not just for human beings but for all substances.

Actuality and Potentiality

Hylemorphism is rooted in Aristotle’s doctrine of actuality and potentiality. Briefly put, actualities are the powers and characteristics that substances possess as a matter of course. For example, bats posses the actuality of navigating via echolocation. And humans possess the actuality of reasoning. Potentialities are the range of characteristics or powers that a thing can possess given certain modifications or changes. To utilize the bat example again, a bat hanging from the top of a cave is potentially flying. A human being sleeping is a human being with the potential to be running. It is form that is the principle of actuality and matter is the principle of potentiality. A form allows substances to have the range of powers they have. And matter is the principle which limits actualities. This is because matter is subject to limitations of space and time

The distinction between actuality and potentiality (which leads to the distinction between matter and form) is necessary, according to Aristotle, to account for any type of change in the material world. Thus it is not just the human being but all substances that exhibit the unity of matter and form. This does not mean, however, that all substances have souls. The unity of the human person is especially unique because the form of the human person is immaterial.[i]

Practical Implications

We can now see, after looking at the biblical and philosophical evidence, why the catechism declares the human person to be at “once corporeal and spiritual” and that the soul is said to be “the form of the body.” There is no question on this view about two substances interacting. This is because the body would not be the body without the form and form would not have concrete existence without a body for it to be the form of.  God created this unity from the beginning and it is because of this integral and immense unity that death is so traumatic for us and resurrection is so glorious.

The unity of the material and immaterial grounds many of our responsibilities in our secular and religious lives. Those who misunderstand the unity of body and soul are in danger of misunderstanding crucial moral and religious doctrines. I will address the implications of the unity of body and soul in future installments. I will also develop other key aspects of human nature along the way.  In the next installment, I will explore what this understanding of human nature entails regarding the reception of God’s grace.

[i]For further reading on these subjects, see: and

Share on facebook
Share on google
Share on twitter
Share on linkedin
Share on pinterest

Leave a Comment

Your email address will not be published. Required fields are marked *