Sure, right now I’m a complex entity - but I didn’t start out that way. No-one would have accused me of being “fully” a person, in the sense of being completely in control and aware of the consequences of my actions, when I was freshly out of the womb…and probably not until I had attained the age of legal majority, if you’re talking court appearances. Why do you think there are separate courts, separate laws and separate penalties for underage offenders?
But that’s the whole point of parsimony - the explanatory power of simpler mechanisms when we try to understand more complex ones. You are positing an immensely complex entity as a brute fact, which is as far from parsimony as you can get. Why do you have such a problem with the possibility that reasoning ability is comprised of simpler processes interacting in a beautifully intricate neurochemical ballet?
The complexity of the human soul must be manifested in very complex chemical, physical, and neurological functions. Again, all matter is “sacramental” in nature, reflecting the metaphysical realities. Somehow God has allowed his spiritual realities to be manifested through and in matter. Science is nothing more than the human mind analyzing God’s creative power, will, and mind manifested in matter. And what that physical expression looks like is often profound, complex, intricately complex, enigmatic, and mysterious. We observe God’s reflection of eternal truths when we analyze the functions and laws of his material world; we don’t observe a perfectly efficient and perfectly ordered world because the spiritual realities of sin and spiritual warfare after the Fall aren’t perfectly efficient and perfectly ordered. If God wanted to create a perfectly ordered world He would and could have done so.
Different parts of my mind certainly do entertain different thoughts and awarenesses. Neurological investigations even bear out the fact that different areas of the brain perform different functions. If we had such fundamental unity of mind as you posit, where would be the fuel for countless human dramas played out in history and literature? Haven’t you ever experienced conflicting desires? And why should not atomic, electrical and other chemical interactions result in the mental fluctuations we all experience on a daily basis? The very fact that particular parts of our neurological control systems and mental states are affected by the ingestion or absorption of particular chemicals - like ethanol, caffeine or nicotine, to name only the most common examples - should point to the fact that minds are composed of complex physical interactions.
If I were merely appealing to authority, I would simply have cited the works of some of these superior minds, rather than explaining my own understanding of the argument in my own words…