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Glossary 1 min read

What is Cartesian Doubt?

Cartesian doubt is a systematic, methodological process of skepticism used to identify and discard any beliefs that carry even the slightest vulnerability to doubt, aiming to uncover an absolute foundation for truth.

By Philosopheasy Published on May 21, 2026

Methodological Skepticism

Cartesian doubt, named after the French philosopher René Descartes, is not a form of permanent skepticism or nihilism. Instead, it is a methodological tool. Descartes compared the process to emptying a basket of apples to check for rot. If you suspect some apples are rotten, the safest course of action is to dump them all out and only put back the ones you are absolutely certain are fresh. Similarly, Cartesian doubt involves temporarily suspending belief in everything you think you know, in order to rebuild your knowledge on a foundation of absolute certainty.


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The Three Waves of Doubt

Descartes structured his doubt into three progressive waves, each more radical than the last. The first wave targets sensory perception, acknowledging that our senses can be fooled by illusions. The second wave is the dream argument, which suggests that we cannot reliably distinguish between waking life and a highly realistic dream. The third and final wave is the Evil Demon hypothesis, which challenges our rational and mathematical intuitions by imagining an all-powerful deceiver. Through these waves, Cartesian doubt clears away all unexamined assumptions, paving the way for the discovery of the Cogito.

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