The Quest for Certainty
In his 1641 work, Meditations on First Philosophy, René Descartes set out on an ambitious intellectual journey: to rebuild human knowledge from the ground up. To achieve this, he realized he needed to demolish all of his existing beliefs and see if any could survive the most rigorous skepticism imaginable. This method is known as Cartesian doubt.
The Stages of Doubt
Descartes did not doubt his beliefs randomly. Instead, he attacked the foundations of his knowledge in stages. First, he questioned his senses, noting that they occasionally deceive us, such as when a distant tower looks round but is actually square. Second, he introduced the dream argument, pointing out that we often have vivid sensory experiences while asleep that feel entirely real. Finally, to doubt even the most basic mathematical and logical truths, Descartes introduced his most radical hypothesis: the Evil Demon.
The Malicious Deceiver
Descartes imagined an all-powerful, clever, and malicious demon (or genius malignus) who dedicates all of its energy to deceiving him. Under this hypothesis, the physical world, the sky, the air, the earth, and even Descartes' own body are nothing but illusions generated by the demon to trap his judgment. Even simple mathematical truths, like two plus three equaling five, could be a deception implanted by this malevolent force.
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Join NowThe Discovery of the Cogito
Just when skepticism seems absolute, Descartes discovers a truth that the demon cannot possibly corrupt. Even if the demon is deceiving him about everything else, the demon cannot make Descartes non-existent as long as Descartes is thinking. To be deceived, one must exist. This realization is formulated as "Cogito, ergo sum"—"I think, therefore I am." It serves as the bedrock upon which Descartes begins to reconstruct his entire philosophical system.