Meditations on First Philosophy
René Descartes · 1641
"By systematically doubting everything that can possibly be doubted, including the reliability of the senses, Descartes arrives at one thing that survives the doubt — the fact that he is thinking, and therefore exists, cogito ergo sum — and builds all further certain knowledge back up from that single indubitable foundation using reason alone."
Descartes sets out to find a foundation for knowledge that is completely certain, immune to even the most extreme skeptical challenge. His method is radical doubt: reject anything that can be doubted at all, even slightly, including the evidence of the senses, which sometimes deceive us, and even basic mathematical truths, by imagining a powerful deceiver could be tricking him about those too. What survives this maximal doubt is the act of doubting itself — the fact that something is doing the doubting proves that thing exists, whatever else turns out to be false.
From this single certain point, the cogito, Descartes tries to rebuild knowledge deductively, using reason rather than the senses as the primary tool, since the senses were exactly what got doubted away in the first place. This is the core rationalist move: privileging clear and distinct ideas grasped by pure reason, like mathematical truths, over knowledge derived from potentially unreliable sensory experience, the opposite emphasis from Locke's empiricism. Later rationalists and empiricists spent the next century arguing over whether Descartes's foundation actually holds, and whether reason alone, without sensory input, can really rebuild a full picture of the world.
What survives Descartes's process of radical doubt in the Meditations?
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The explanation above is written with AI assistance. These are the originals — go to them to check it.
- Meditations on First Philosophy (full text)Project Gutenberg
- Descartes' EpistemologyStanford Encyclopedia of Philosophy
An Essay Concerning Human Understanding
"The mind at birth is a blank slate, tabula rasa, with no innate ideas — all knowledge, without exception, is built up from sensory experience and the mind's reflection on that experience."