Until recent history, the immaterial dimension of a human being, that is, the soul, had been regarded as the ground of human personhood and the anchor of human value. Philosophers from Plato and Aristotle to Aquinas and Descartes championed dualism and argued that the soul was the essence of a person and contained the very form of one’s being, that is, the principle of personal individuation and development.

The Medieval Christian philosopher/theologians saw in the soul an indication of what the Bible calls the Image of God in man. The soul was the seat of all human capacities and in particular one’s capacity to relate to God. It made sense that, since God is immaterial, he would create men and women with an immaterial component to their nature as well so that they might connect with him and know his purposes for their lives.
           
This notion began to erode with the onset of the Age of Reason, and the erosion gained impetus under the influence of Darwin’s theory of evolution. The consequent turn toward naturalism and physicalism among twentieth century scientists and philosophers was slow but sure. Abandoning the notion of dualism due to a commitment to naturalism and physicalism, the scientific and philosophical communities attempted to define human personhood in terms of certain functions such as self-motivated activity, the ability to communicate, and self-awareness. A moment’s reflection upon this reasoning should give us serious pause.         

If applied to the human fetus, this reasoning would find nothing immoral about killing the fetus for any or no reason at any point during gestation. In addition, infants and even toddlers might be at risk since they would be lacking in some of the above functional criteria. But to be consistent with functional definitions of personhood, we must also apply them to those who have lost these functions, yet continue to live. For instance, an elderly woman in the advanced stages of Alzheimer’s disease, who has lost a number of the above functions, would forfeit her personhood and likely qualify for forced euthanasia.

Finally, it would seem that all kinds of harm might be inflicted with impunity upon people who are unconscious, asleep, under general anesthesia, comatose, or in a persistent vegetative state since their first order capacities to experience sensations, communicate, and to be self-aware have been impaired or destroyed. These are the absurdities to which a functional definition of personhood takes us, and a functional definition of personhood is all that naturalism, physicalism, and scientism can offer.

Some thinkers, wishing to have their cake and eat it too, have argued that immaterial mental states somehow emerge from the brain and nervous system when these physical structures achieve a certain level of development. They posit that we are indeed our brains and mental states are no more than "epiphenomenon" in the same sense that sparks are to fire. Mental states, therefore, are simply an ancillary result of brain activity, properties of the brain that have no causal powers of their own. This position is called "property dualism." It fails for two reasons. First, it still requires that we ground personhood by means of functions since it still considers humans to be essentially physical things. In addition, the claim that such mental entities are non-causal in nature defies what we know about the mind, which obviously has causal powers. 

Furthermore, we have seen in Part 2 of our series ("Evidence For the Soul") that it is most reasonable to accept a robust dualism as the correct picture of human nature. Philosophical reflection on our first person awareness provides us with evidence that supports the existence of a non-emergent soul/mind with causal powers. Furtherhermore, this is the view revealed in the early chapters of Genesis when God breathes life directly into the nostrils of the inanimate body of the man that he formed from the mud (Genesis 2:7). It was not until then that Adam came alive.

So philosophy and theology intersect to give us the knowledge that we are not just our bodies and our brains, but we are living souls, possessing the breath of God within us and bearing God's Image as a result. Recovering a robust notion of this composite nature of human beings and the reality of the Image of God in them is the only path toward a humane ethic that recognizes the full personhood of every individual from conception to the grave.

"The soul is most like the divine and immortal and intellectual and uniform and indissoluble and ever unchanging" (Plato).

"You don't have a soul. You are a soul. You have a body" (C.S.Lewis).

"My soul magnifies the Lord, and my spirit rejoices in God my Savior" (Luke 1:46-47).