Foucault went back to René Descartes (1596–1650) to show that the designation of insanity was the product of an age that valued reason in a certain form. He thought that medical practice in general required a certain kind of seeing before specific pathologies could be detected. In The Order of Things (1966), he argued that part of the development of economics, science, and linguistics in the eighteenth and nineteenth centuries entailed the invention of the idea of “man” as a universal subject. (Man, the universal subject, was supposed to be always the same and always rational.)