In this paper, I’ll discuss the philosophical debate that took place between Michel Foucault and his student Jacques Derrida on Rene Descartes’ doctrine of cogito. In my exposition, I shall discuss Descartes’ contributions to modern philosophy in twofold manner, namely the central and the marginal doctrines. At the centre of Cartesian modernity, there is cogito and the emergence of human subjectivity, reason and rationalism, truth in terms of clearness and distinctness and the existence of God. On the margins, we come across madness, deception, demon and so forth. These are the issues, which are subjected to rigorous criticism and rejection by Foucault on the one hand, and Derrida on the other. The debate tries to reallocate the central and the marginal themes by overemphasizing the marginal issues and thereby moving one step forward. However, in the process of doing that they have under-emphasized the central doctrines and have gone two steps backward. The ambition lies in paving the way for an internal departure from Cartesian modernity to Foucauldian–Derridean postmodernity. Instead of going to a critical reading of Derrida’s interpretation of the Cartesian text step by step and his debate with Foucault, the present paper hopes to provide some of the basic issues involved in Descartes and Foucauldian–Derridean reaction to those issues. In my attempt to articulate the debate, I shall furnish some clarifications, annotations and summations that may be useful for the limited end of preliminary acquaintance with Descartes on the one hand, and Foucault and Derrida on the other.