We are now going to look at the most famous representative of the dualist view, the French philosopher René Descartes. Driven by his desire to find an absolute certainty on which to base the search for knowledge, Descartes claimed to have discovered one fact beyond doubt: that he is a thinking thing. This famous argument - called the Cogito after the Latin phrase, “cogito ergo sum” (I think, therefore I am) – tries to establish the mind as a separate substance from the body.

For Descartes, certainty is best supplied by reason. The further the mind is taken away from its proper objects – logic and pure reason – the more likely it is to fall into error. Thus, for Descartes, the purpose of philosophy is to direct the mind away from the confusing images of the senses towards the indubitable truths contained within the mind itself.

This project led Descartes to conclude that the mind was a completely distinct substance from matter. Matter is easily described: it is measurable, has dimensions, can be touched and seen, sometimes smelt and tasted, divided, destroyed and altered. Mind, however, can almost be defined as the opposite of this – in fact, one of the difficulties with Descartes’ definition is that mind seems to have almost no positive qualities. It is invisible, without dimensions, immaterial, unchanging, indivisible and without limit.