In this paper, I discuss the role of diagrammatic thinking within the larger context of cognitive activity as framed by PeirceÕs semiotic theory of and its underpinning realistic ontology. After a short overview of KantÕs scepticism in its historical context, I examine Peirce's attempt to rescue perception as a way to reconceptualize the Kantian "manifold of senses". I argue that PeirceÕs redemption of perception led him to a series of problems that are as fundamental as those that Kant encountered. I contend that the understanding of the difficulties of PeirceÕs epistemology allows us to better grasp the limits and possibilities of diagrammatic thinking.
