In Meditations on First Philosophy, arguably the most influential philosophical text of the 17th century, René Descartes takes the reader on an intellectual journey in order to demonstrate how scholars can build a systematic, scientific understanding of the world through rational deduction. This journey begins when Descartes’s narrator, the Meditator, decides to pretend that nothing he perceives is truly what it appears, prompting him to try “start[ing] right again from the foundations” of knowledge. Next, he famously concludes that he can still be certain of one thing: his own existence. Based on this first principle—“I am a thinking thing”—the Meditator deduces that God and the physical world are real. He also concludes that anything he clearly and distinctly understands through the intellect must be true, an idea that has since become the foundation for the modern scientific method. In fact, Descartes was one of the earliest and most influential intellectuals to argue for the sciences to reach the same level of rigor and certainty as mathematics, and his work has left a deep impact on philosophy and science ever since.
Descartes opens the Meditations with a letter asking for support from France’s leading university, the Sorbonne, and a preface summarizing his arguments. Then, the First Meditation begins with the Meditator pointing out that many of his childhood beliefs have since turned out to be false, and the same might be true of the other ideas he takes for granted now. So he tries to suspend belief in all of them by imagining that he’s dreaming, or that an evil demon is controlling his mind and tricking him into thinking that everything he perceives is real.
In the Second Meditation, the Meditator concludes that—even if he can’t trust anything he sees, remembers, feels, or imagines—he knows for sure that he’s thinking, so he can still be certain of his own existence. Although this hidden, thinking self may seem less real than the things he usually perceives with his senses, it actually strikes closer to the essence of what he really is. The Meditator illustrates this point by imagining a piece of beeswax, which may look cold, hard, and solid at first, but becomes warm and malleable when heated. Thus, the wax’s outward qualities don’t capture the essence of what it is—rather, its essence is simply to be “something extended, flexible, and changeable.” In short, reason is a surer guide to the truth than the senses are.
In the Third Meditation, the Meditator offers his first proof for the existence of God. His argument is complex, and it depends on distinguishing between three kinds of essence: infinite substances, finite substances, and particular things. His argument also distinguishes between two kinds of reality: formal reality (existence) and objective reality (accurate representation). In short, he asks where he could have gotten the idea of an infinite substance like God, and he concludes that there’s only possible explanation: God gave him the idea, which of course means that God is real. The Meditator also deduces that God is perfect and is his creator, so God wouldn’t deceive him about the validity of his perceptions.
In the Fourth Meditation, the Meditator asks why people make judgment errors if their creator is perfect. He concludes that God made the universe perfect, but not every individual in it. People make errors in judgment because their free will is stronger than their intellect: they have absolute freedom to make choices, but they don’t have absolute knowledge about the world. As a result, they frequently (and foolishly) make decisions about things they don’t yet understand. The solution, of course, is his own intellectual and scientific approach: to suspend belief in ideas until we can rationally prove them true. And achieving this kind of proof is merely a matter of perceiving things clearly and distinctly with the intellect.
In the Fifth Meditation, the Meditator presents the basic properties of a triangle (like having three sides and three angles that sum to 180 degrees) as a classic example of clear and distinct rational perception. And by sorting such clear and distinct perceptions from unreliable ones, he concludes that properties like quantity, shape, position, motion, and duration define the essential nature of objects. Then, in the rest of the Fifth Meditation, he goes on to present another argument for God’s existence: by definition, “a supremely perfect being” like God would have every kind of perfection—and since existence is a form of perfection, God must exist.
Finally, in the Sixth Meditation, the Meditator returns to the everyday perceptions that he decided to systematically doubt at the beginning of the book. Now that he’s certain that his clear and distinct rational perceptions are reliable and that God is no deceiver, he knows that his perceptions of physical things—like his own body—must be proof that such real physical things actually exist. He concludes that his body is distinct from his mind but that it requires the mind’s guidance in order to function correctly. And he even admits that there is usually “some truth” in our sense perceptions (like what we see and hear) and sensations (like hunger and pain). These perceptions and sensations sometimes do deceive, but as long as we use the intellect to catch their errors, we can generally trust them. The Meditator ends by rejoicing in his newfound certainty that most of his basic instincts about the world were correct all along.
