The cogito is not really an inference from a premise; it is a performance. In the very act of doubting whether I exist, I exist. Even an omnipotent deceiver cannot deceive nobody.
Objections that became famous:
- Pierre Gassendi: why not “I walk, therefore I am”? (Descartes: because I can doubt I am walking, but not that I seem to.)
- Georg Lichtenberg: we should say “it thinks”, as we say “it rains” — the “I” is an assumption.
- David Hume: introspection finds perceptions, never a perceiver.
- Friedrich Nietzsche: grammar tricks us into positing a doer behind every deed.
- Søren Kierkegaard: if I think, I am a thinker — existence is presupposed, not proven, and existing is something quite different from thinking.
- Martin Heidegger: Descartes asked about the cogito and forgot to ask about the sum — what does it mean to be?
Sententiae
phrases in the originalCogito, ergo sum
Origin. Descartes, first in French (“je pense, donc je suis”, Discourse on Method, 1637), then in Latin in the Principles of Philosophy (1644). — René Descartes
⚠ The Meditations never use this formula — there it is “ego sum, ego existo” (I am, I exist). Augustine had argued “si fallor, sum”.
For the one certainty that survives doubt; the birth of modern subjectivity.
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The inventor of the essay, who made himself the subject of his book — sceptical, curious, tolerant, candid — and asked, “Que sais-je?” — What do I know?
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Persian polymath — physician, metaphysician, logician — whose Canon of Medicine was taught in Europe for 500 years and whose distinction between essence and existence reshaped philosophy in Islam and the Latin West.
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Father of British empiricism and of liberalism — the mind begins as a blank slate, and government rests on the consent of the governed.
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The Viennese-Cambridge philosopher who twice transformed philosophy — first by mapping the limits of what language can say (Tractatus), then by showing that meaning is use in the countless “language games” of ordinary life (Philosophical Investigations).