Philosophy of Mind (Edward Feser, 2005) is an interesting introduction to the Philosophy of Mind and the influence that this subject has had on philosophy at large. Modern philosophers sought a completely material explanation for mankind and cast aside the Western tradition which saw mind as something separate from the brain. Feser's work provides an overview of the different methods used to attack the mind/brain problem.
It seems to me that this mind/brain problem is one of the big gaps between modern and classical liberalism. Modern dialectical materialism held that science has a complete explanation for everything. The thing we think of as a mind is just an illusion caused by chemical processes. The classical world saw science as a useful tool, but not as a complete perfect system that describes everything. To the classical liberal, the edges will always be blurry.
Feser's short sweet introduction to the Philosophy of Mind takes a road through the various attempts to create a complete material description of the mind. At the end of the work, the mind remains blurry hinting that perhaps the classical tradition was right after all.