Cogito — Abbreviation of René Descartes’s famous formula “Cogito, ergo sum” (“I think, therefore I am”), which names the first indubitable certainty reached through methodical doubt. The term derives from the Latin verb cogitare (“to think,” “to consider”). The French formulation — “Je pense, donc je suis” — appears in the Discourse on the Method (1637); the reasoning is taken up again in the Meditations on First Philosophy (1641), where Descartes states it as “Ego sum, ego existo” (“I am, I exist”); and the canonical Latin version appears in the Principles of Philosophy (1644). The argument runs as follows: by subjecting all of his knowledge to radical doubt — even supposing that an evil genius systematically deceives him — Descartes realizes there is one thing he cannot doubt, since the very act of doubting presupposes someone who doubts. So long as I think, it is impossible that I do not exist. The cogito thus becomes the Archimedean point, the unshakable foundation on which the edifice of knowledge is built, and it marks the turn toward modern subjectivism: the certainty of the thinking subject precedes and guarantees the certainty of the external world. From this follows the definition of the self as res cogitans (“thinking thing”), distinct from res extensa (“extended thing,” body and matter), a distinction that gives rise to the famous problem of mind-body dualism. The cogito is directly tied to methodical doubt, the instrument that leads to it, and to rationalism, the tradition that recognizes reason as the primary source of certain knowledge.
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