This essay will consider some of the issues that have been posed by Foucault and Derrida concerning their disagreement on the Cartesian cogito. I will argue that what is at stake this debate is the question of where exclusion takes place and what exactly its nature is. As we shall see, Derrida's argument is that exclusion is connected with certainty and objectification, and this is the meaning of the discussion of hyperbolic doubt Descartes. The sheltering of the cogito from hyperbolic wanderings amounts to an act of mastery which is unjustifiable. The debate also reflects a difference between the two philosophers as far as historicity and critique are concerned. Nevertheless, it shows a common theme that runs throughout their philosophy; that is, the dangers the movement of thought to function within an economy, along with the different levels of inclusion and exclusion the realm of meaning its relation to what does not yet belong to it. Both thinkers want to disrupt totality, and thus emphasize the opening of thought as opposed to its closing upon itself, as it relates itself to its objectifications as total and absolute determinations. The debate began with Derrida's critique of Foucault's first book on madness.1 Derrida's critique focused on two main points: on Foucault's reading of Descartes' First Meditation the introduction to his book, and on some methodological and philosophical issues dealing with the whole project of Foucault's analysis. His discussion of Descartes concentrates on the passage from the example of madness to the example of dreams, and how this relates to their status, continuity, or rupture Descartes' system. Descartes' First Meditation is about doubt as far as the senses are concerned. As Descartes says, though we learn through the senses, we have been deceived by them as well and this constitutes sufficient reason not to trust them at all. Nevertheless, he speculates that there are things that we cannot have any doubt about. example, there is the fact that I am here, seated by the fire, attired a dressing gown, having this paper my hands and other similar matters.2 Only persons devoid of sense who think they are kings when they are poor can have doubts about these things. Descartes continues: But they are mad, and I should not be any the less insane were I to follow examples so extravagant.3 However, Descartes says the next paragraph, when we sleep and dream we experience things that those who are insane do when they are awake. For example, we may dream that we sit next to the fire while reality we are bed. Though, he remarks, it is true that what happens our waking moments appears more clear, there are not clear indications on the basis of which we can distinguish the status of sleep from that of wakefulness. At this, Descartes says, he is lost astonishment; And my astonishment is such that it is almost capable of persuading me that I now dream.4 According to Foucault's reading, Descartes' analysis, madness and dreams or sensation have a different status. As he put it, in the economy of doubt there is a fundamental disequilibrium between madness on one side and error on the other. Their situation is different relation to both truth and inquiry; dream and illusion are surmounted through the very structure of truth; but madness is excluded by the subject who doubts.5 Derrida challenges this reading of Descartes. According to Derrida, Descartes does not exclude madness from the interiority of thinking. Thus, the relation of madness and dreams to sensation Descartes' text is not one of philosophical and methodological rupture. Derrida argues, on the contrary, that Descartes is not moving from the example of madness to the example of dreams, because he decides that madness should be excluded from the possibility of thinking. Rather, the gesture is a pedagogical and a rhetorical one. Therefore, where Foucault finds a definite conclusion, Derrida sees the continuation of the issue. …