What are we to make of the cogito (cogito ergo sum) today, as the walls of Cartesian philosophy crumble around us? The enduring foundation of the cogito is consciousness. It is in virtue of a particular phenomenological structure that an experience is conscious rather than unconscious. Drawing on an analysis of that structure, the cogito is given a new explication that synthesizes phenomenological, epistemological, logical, and ontological elements. What, then, is the structure of conscious thinking on which the cogito draws? (...) What kind of certainty does the experience of thinking give one about one's thinking and about one's existence? What form of inference is the cogito, and what is the source of its validity and soundness? Does the cogito itself lead to an ontology of mind and body like Descartes's dualism? The discussion begins with Descartes's own careful formulations of some of these issues. Then the cogito is parsed into several different principles, the phenomenological principle emerging as basic. In due course the analysis sifts through Husserl's epistemology, Hintikka's logic (or pragmatics) of the cogito, and Kaplan's logic of demonstratives, as these bear specifically on the cogito. (shrink)