  The classical emphasis originates in Plato’s Phaedo. 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’. It is their connection with intelligibility that is relevant to the philosophy of mind. Because Forms are the grounds of intelligibility, they are what the intellect must grasp in the process of understanding. In Phaedo 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. It may take many reincarnations before this is achieved. Plato’s dualism is not, therefore, simply a doctrine in the philosophy of mind, but an integral part of his whole metaphysics.