When philosophy teachers present the ‘-ism's’ pertinent to mind–body relations, and are still at the broad-brush stage, quite often one finds them pairing Plato and Descartes as the two most eminent dualists of our Western tradition. As Plato to the through-and-through materialist Democritus, so Descartes to Gassendi, it is often suggested – reasonably, perhaps. As the modern non-reductive materialist to his Cartesian bête noire, so Aristotle to Plato on soul–body relations, we are sometimes told – a misleading analogy, some think. For the purpose of contrast with various non-dualist views it may seem useful to group Plato's dualism and that of Descartes together, and in many contexts their differences may not matter. But if one simply compares the theories with each other, not with any third system, the differences are fascinating and seem important.

Of course there are similarities to sustain the initial pairing. Both philosophers argue that we consist of something incorporeal, whether one calls it ‘mind’ or ‘soul’, which for the time being is somehow united with a body that is part of the physical world. Both identify the self, the ‘I’, with the incorporeal member of this alliance. Both hold that my mind or soul will survive the demise of the body by means of which I set down these words for others by means of their bodies to access. Both may be understood as holding that the mind or soul can exist altogether independently of body, though Plato may have changed position on this point. Both are concerned with the immortality of the soul.