Formuloval nejspojitost ducha a těla (mind/ body), mimo člověka, který má duši, je veškerá příroda připodobněna k automatům - strojům. Položil zásady vědecké metody, významně se podílel na rozvoji matematiky a fyziky, na vytvoření číselné reprezentace geometrických objektů (kartézská soustava souřadnic), na vzniku analytické geometrie a na matematizaci optiky.
Descartes held that the body is basically a machine, which is fundamentally different from the mind. He had various tests which show that machines cannot think. This raises interesting questions about artificial intelligence and computers. Many philosophers after Descartes proposed alternative systems to avoid the difficulties of Cartesian dualism, including Spinoza, Leibniz and others.
“it is quite remarkable that there are no men so dull-witted or stupid – and this includes even madmen – that they are incapable of arranging various words and sounds together and forming an utterance from them in order to make their thoughts understood; whereas there is no other animal however perfect and well endowed it may be, that can do the like. This does not happen because they lack the necessary organs, for we see that magpies and parrots can utter words as we do, and yet they cannot speak as we do: that is, they cannot show that they are thinking what they are saying. On the other hand, men born deaf and dumb, and thus deprived of speech-organs as much as the beasts or even more so, normally invent their own signs to make themselves understood by those who, being regularly in their company, have the time to learn their language. This shows not merely that the beasts have less reason than men, but that they have no reason at all. For it patently requires very little reason to speak; and since as much inequality can be observed among the animals of a given species as among human beings, and some animals are more easily trained than others, it would be incredible that a superior specimen of the monkey or parrot species should not be able to speak as well as the stupidest child – or at least as well as a child with a defective brain – if their souls were not completely different in nature from ours.” (Descartes 1637, p. 140)