Argument concerning Descartes
Foucault writes at the start of the second chapter of Madness and Civilization of a strange violent event that silenced madness at the end of the renaissance and the beginning of the classical age. He then discusses the treatment of madness by Descartes in the Meditations on First Philosophy. Descartes, after having doubted the existence of the external world and that of his own body, poses the objection of madness to himself. For Descartes, denying that "these hands and this body belong to me" would be equivalent to maintaining, as do "those senseless people" who think they "are dressed in purple and gold while they are all naked, or imagine themselves to be jugs or have a body of glass." And he continues: "But they are fools (amentes), and I would be no less extravagant (demens) than them if I followed their example". Subsequently, Descartes tackles the "dream hypothesis", asking whether perception is only a dream and not something real, unlike the incontrovertible truths of mathematics. But even the latter are attacked, with the use of the further objection that, in addition to sensible perceptions, also certainties and rational reasons are nothing more than a deception on the part of an evil demon. According to Foucault, the experience of madness and the "hyperbolic doubt" are completely different and not comparable, as the experience of the madman is not even to be taken into consideration, "since I think",[8] while the madman does not. Foucault's conclusion is that the Cartesian cogito was the premise of the decree of exclusion of madness and the "great internment". For Foucault this exclusion of madness by Descartes leads to a cogito that is more or less arbitrarily self-assured of its own rationality.
Derrida argues that Descartes might appear to dismiss madness at the point of the meditation to which Foucault refers but shortly after this takes madness seriously as a ground for doubt when he considers the possibility of there being an evil demon controlling his thoughts. Derrida argues that Descartes includes the possibility of his own madness when he hypothesises that an evil demon could corrupt even the most assured and reasonable judgements he can make, such as those of basic arithmetic. Hence, the procedure of Descartes' Second Meditation aims to demonstrate that cogito, ergo sum remains true even if I am driven mad by the evil genius: "Whether I am mad or not, cogito, sum". "The act of the cogito is valid even if I am mad, even if my thought is in every part mad."[9] For Derrida, Cartesian reason, rather than excluding that which differs from it, recognizes the threatening presence of madness. In this way, reason perceives the 'other', the different from itself, within itself. Derrida argues that madness is not subject to an arbitrary exclusion by Descartes but that once Descartes earnestly but momentarily enters into the hypothesis of the evil demon he must be reassured by the ordered operative norms of his language and project of self-reflection.