People perceive a natural dualism between mind and brain. But then assume that this means the mind, or that at least parts our "self", exist independently of the brain.
They call it our spirit, soul, essence, and other more mystical sounding words, most of which are simply the same idea represented in the language of different cultures. Tea is a nice drink, but calling it Chimarrão, Tee, Te, Teh, Thea, Herbata, Entèh, Tēja, Tsai, Sah, Chā, Shaah, Chahen, Chāy, Tenneru, Choy, or Liptons does not make it more or less than it was when you poured it into your cup.
The claim most often made is that the spirit is the "non physical" part of ourselves and when pressed people often use analogies to energy, magnetism, light, radio, sound, etc which is false because all these are physical in nature. Easily tested because they can all be generated and measured by physical methods.
- If something interacts with with the physical world it must do so via shared physical properties
- If something has physical properties it's physical, be it a force or a substance
- Therefore ANYTHING that interacts with or is impacted by something physical MUST BE physical itself.
The main proof offered, however, for the existence of a non physical self is the inability to physically locate elements of self in our physical forms. People support the argument for soul or mind separate from the body by the thought experiment of taking the brain apart and attempting to identify, by examination, where a particular faculty or memory exists - the use a gross mechanical method to detect a subtle physical property or behaviour.
I'm amazed that this example even gets put forward, it's akin to grinding my iphone into dust and asking someone to sift through it to find the video of my cat that I had stored in it. That failure would not prove my cat video was a metaphysical entity any more than failure to find a particle of consciousness in a dissected brain proves that consciousness is metaphysical.
In the same way playing the video of my cat and hearing it meow does not mean there was a sound in my iphone all along. The sound emerged as a result of a complex set of interactions, consistent, repeatable and (to someone with sufficient understanding of digital electronics) fully explainable. Even the waves beating on the shore generate sound, but we dont think sea water is made of sound or that the sound of the waves exists independent of the water and shore.
Our lack of a similarly complete explanation of behaviours emergent from/generated by the human brain does not mean such explanations are impossible, simply that they are outside the scope of our understanding. The fact however that we have observed and created similar phenomena in electronic systems indicates that the only difference between the examples we can explain and those that we cant is one of scale.
The attempt to mechanically examine for elements of self fails as a test of anything even before we consider the nature of one thing emergent from another because behaviours and faculties are contextual.
For example, my ability to play chess (badly) would not exist without the concept of a chess board, my spatial awareness, my memory of the rules, my personal values (fear of loss, agression, empathy with my opponent, etc), my capacity for logic etc, etc, etc.
So to try to identify what single part of a brain holds my chess ability will fail because it's a combination or interaction of various other faculties that creates that ability.
We could try to identify what parts of the brain are necessary for the skill, and while direct experimentation is not practical - observation of people who have suffered physical trauma to their brain allows us to make such identifications. We know for instance that hypocampus is a key component in memory and spatial reasoning.
My understanding of chess and my ability to play it, my chess faculty if you like, is an emergent behaviour from a very complex physical system. However, a purely mechanical examination of that system will never expose that faculty or it's atomic components (assuming it can be broken into meaningful particles).