The position I hold can best be described as Cartesian substance dualism (hereafter SD). While I do not take on everything Descartes did, I do take on the basic thesis that the “I” of personhood is identical to the “soul,” and that there are two kinds of substances, immaterial and material. In this essay, I give a brief positive argument for and account of SD, while attempting to address philosophical and theological objections against it.
While there are arguments for a broad kind of dualism, there is at least one argument for SD specifically that I take to be successful, and this is the modal argument. Briefly, it states:
1. The law of identity is true: If x is identical to y, then whatever is true of x is true of y and vice versa.
2. I can strongly conceive of myself as existing disembodied.
3. If I can strongly conceive of some state of affairs S that S possibly obtains, then I have good grounds for believing that S is possible.
4. Therefore, I have good grounds for believing of myself that it is possible for me to exist and be disembodied.
5. If some entity x is such that it is possible for x to exist without y, then (i) x is not identical to y, and (ii) y is not essential to x.
6. My body (or brain) is not such that it is possible to exist disembodied, i.e., my body (or brain) is essentially physical.
7. Therefore, I have good grounds for believing of myself that I am not identical to my body (or brain) and that my physical body is not essential to me.
My account of SD is that the mind affects the brain, and the brain affects the mind. The mind does so at the level of agent-causation of intentions; it is the way the mind interacts with the physical world. The brain and body do so at the level of physical ability; if the body is injured such that it cannot physically function correctly or is otherwise diminished, then the soul’s (mind’s) ability to interact with the physical world is diminished as well.
There are objections both to this argument and SD in general. First, premises (2) and (3) may come into question. Several, such as Peter van Inwagen, question whether someone’s modal intuition can be such that he strongly conceives of himself as disembodied. Perhaps he merely has a lack of awareness that such a state of affairs is impossible (whether metaphysically or otherwise); but such a lack hardly constitutes a strong conceivability, but rather a weak one. However, it does seem that we can intuit that what we are is not this body; it seems we can have a positive conception after all. We do have such strong conceptions, modally, in other areas, so even if van Inwagen does not, why can I not do so?
Another potential objection comes to (3) in that perhaps it is the case that one can strongly conceive of something, and it may not be possible. The answer is to grant that this is so; however, the argument does not need a guarantee that the state of affairs is really possible; it only needs to be reliable such that one has justificatory grounds for thinking it is possible. It seems to me that this objection does not remove such justification; analogously, knowledge does not require certainty.
The most famous objection against SD is the interaction problem, which asks proponents how it is the immaterial can interact with the material. The first response is to note that everyone, save truly reductive materialists, has this problem (this is so when brain states give rise to mental properties, for example). Thus, a failure to have a definitive answer does not necessarily count decisively against it. Second, it should not affect Christians, as all orthodox Christians believe God, an immaterial being, created and acts on the material world. Third, it may be that the interaction is direct and immediate, and thus the question of the process that intervenes between the immaterial and material is a non-starter, and hence a category mistake. Fourth, we do not usually require that we know how something works in order to know that it works. It seems this may be an unfair requirement of proponents of SD in order to be justified in holding SD. Finally, it should be acknowledged that it is not clear precisely how the interaction between the soul and body takes place. Nonetheless, in showing what appears to be a coherent account, as explained above, proponents of SD can claim that while we are unsure of how it takes place, the way in which it may interact can be coherently discussed.
There are also theological objections to SD. Consider that if SD is correct, then the body is not necessary; if this is the case, then the resurrection in the eschaton is simply an added bonus. Yet this is not how the Bible seems to portray the resurrection: in fact, in 1 Corinthians 15, the resurrected body seems to be the primary goal. It is true that SD makes the resurrection unnecessary for a human person to be a person. Yet, even on SD, one can claim the resurrection is necessary in order for a human person to be what God designed him to be: embodied. This necessity, although colloquial, is nonetheless quite important. The endgame of Christianity is that God will restore what sin has damaged; God will have the victory. This includes the spiritual (e.g., the souls of men) as well as the physical (the earthly creation and physical universe). The kind of character God has is such that he will restore our bodies, either to judgment or reward. As such, the resurrection body we will have, although not metaphysically necessary to our mere existence, ensures we will have the quality of life we were meant to have.
 J. P. Moreland, The Soul: How We Know It’s Real and Why It Matters (Chicago: Moody Publishers, 2014), 125-26.