Behaviourism, functionalism, mind-brain identity theory and the computational theory of mind are examples of how materialists attempt to explain how this can be so.The most common factor in such theories is the attempt to explicate the nature of mind and consciousness in terms of their ability to directly or indirectly modify behaviour, but there are versions of materialism that try to tie the mental to the physical without explicitly explaining the mental in terms of its behaviour-modifying role.The mind-body problem is the problem: what is the relationship between mind and body?Or alternatively: what is the relationship between mental properties and physical properties?In general, the idea is that, for some particular domain, there are two fundamental kinds or categories of things or principles.In theology, for example a ‘dualist’ is someone who believes that Good and Evil—or God and the Devil—are independent and more or less equal forces in the world.The seemingly intractable nature of these problems have given rise to many different philosophical views.
Because Forms are the grounds of intelligibility, they are what the intellect must grasp in the process of understanding.
In Plato presents a variety of arguments for the immortality of the soul, but the one that is relevant for our purposes is that the intellect is immaterial because Forms are immaterial and intellect must have an affinity with the Forms it apprehends (78b4–84b8).
This affinity is so strong that the soul strives to leave the body in which it is imprisoned and to dwell in the realm of Forms.
In the classical and mediaeval periods, it was the intellect that was thought to be most obviously resistant to a materialistic account: from Descartes on, the main stumbling block to materialist monism was supposed to be ‘consciousness’, of which phenomenal consciousness or sensation came to be considered as the paradigm instance. Plato believed that the true substances are not physical bodies, which are ephemeral, but the eternal Forms of which bodies are imperfect copies.
These Forms not only make the world possible, they also make it intelligible, because they perform the role of universals, or what Frege called ‘concepts'.