The Mind-Body Problem; Monism Vs. Dualism
A History of Debate
The question of what we perceive as, "The mind," and it's relationship to the Physiology of the grey matter that comprises most of the brain is an old metaphysical gem. It was certainly debated in Ancient Athens and probably became a topic of discussion from observations involving Traumatic Brain Injury and the consequent behavioral and cognitive changes manifested by the injured party. it is likely that the proximity of the brain to the sense organs also led to the conclusion that our conscious experience is connected to the physical state of our material brains.
The mind-body problem is an inquiry into this undeniable connection but also into the possibility that our minds might be something more than the mere conscious projections of our brains. Are we more than mere synaptic firings and endorphin chemical transmission at our essence? Is there something within us that might survive our deaths, something we might call a soul?
Dualism and Physical
There are two distinct positions concerning the preponderance of this issue, Dualism and Monism, both with a few sub-distinctions regarding hypothetic variations.
Dualism is proposed to us in three classical forms all of which are distinguished merely by pedantic variations;
Cartesian Dualism so named after Rene Descartes, the 17th century French Philosopher and Anatomist, maintains that though the brain provides the matrix for intellect, the mind is a non-physical entity from which consciousness arises.
Substance Dualism retains the mind as separate from the brain, and likewise not encumbered by the laws of Physics as the material brain is.
Property Dualism maintains that physical laws are universal but cannot be used to explain the mind like they are used to explain the brain.
Monism likewise has been proposed in three versions but with much less nuance differentiating them it's forms;
Physicalism is the proposal that the mind is composed of organized matter and is thus can be inferred to be more or less identical to the brain or a projected illusion arising from this organized matter.
Idealism divorces itself from both Physicalism and all forms of Dualism. It holds that only thought is of importance. Reality is a mental construct and the mental constructs can not be known in any way that is divorced from the mind. Thought is independent of any material components.
Neutral Monism does not draw a distinction between the brain and the mind and maintains that they are the manifestations of an essence that is unlike either the brain or the mind independently.
Evidence for Physicalism
Physicalism is the one version of these three hypothesis that could be considered entirely materialist. That is the contention that observable and potentially observable interactions between matter and energy account for everything that we regard as self. As such, the direct implication is that there is no existence beyond our physical existence, no eternal soul, and no ineffable essence. This is the position that I take and I'd like to outline a few empirical facts that buttress this view.
Firstly, if one takes the position that there is some non material, "ether," that is eternal and what Theology would call a soul, given evolutionary common descent, where is the species demarcation as to which organisms are imbued with a soul and which are not. Did our cousins, the early hominid like creatures such as Australopithecines, Neanderthals, and Cro Magnums have souls? If so do other higher primates such as Chimps and Bonobos? Where is the line drawn or does everything with a nervous system also have a soul? This is an proposal with which most Theists are not comfortable.
Secondly, a three-to four day old Blastocyst, a collection of about 150 cells that constitute the first stage of Embryological development can and do splint into two separate embryos that will become identical twins. If life begins at conception and a soul is bound to life; from where does the second soul come during this in utero phenomena. What's more, the reverse also occurs. Two separate fertilized blastocysts can merge into an Embryonic Chimera. In this case where does the second soul go? While it is true that because Embryonic Chimeraas have two differing sets of DNA they do not usually survive to parturition, but they do survive and continue to grow in utero for a time (and sometimes develop fully) which still begs the question regarding this odd type of soul calculus.
And lastly, evidence from Traumatic Brain Injuries, seems to argue against any stance but Physicalism. When one part of the brain is damaged and becomes non-functional we know that all manner of impairment results. Who that person was; their abilities, temperament, personality, their very essence can change. When another part of the brain is damaged an equally drastic change can occur. And yet we are to suppose, in the cases of Dualism, Idealism, and Neutral Monism that when the brain dies in it's entirety there is some intact essence stowed away and able to raise off as a non-material thinking, conscious entity.
While I do not particularly invite the idea of Nothingness as described by Sartre, and likewise do not discount entirely the possibility of consciousness surviving physical death by virtue of some mechanism we don't yet understand engendered in a substance we don't yet know how to detect, I find it unlikely by virtue of the above arguments.
But hey, I like surprises.