Today we are talking about the philosopher Rene Descartes and his famous statement: Cogito, ergo sum. Before we get to Descartes, let’s take a step back. Have you ever questioned whether your senses are reliable? You see a mirage in the desert, hear an echo in an empty room, or even wake up from a dream that felt incredibly real. The English philosopher Francis Bacon already expressed doubt about our ability to perceive the world objectively. But Descartes took this skepticism to an extreme.
If our senses sometimes deceive us, how can we ever be sure when they’re telling the truth? Descartes concluded that we must doubt everything. He embarked on a mental experiment. First, he doubted his senses—after all, they had misled him before. Then, he extended this doubt even further: What if everything he perceived was just an illusion? What if the world itself was a mere dream? And if that were possible, what if even mathematical principles—things as fundamental as 2+2=4—could be false?
By following this extreme skepticism, Descartes arrived at one undeniable truth: he was doubting. And in order to doubt, he had to be thinking. And if he was thinking, then he must exist. This led to his most famous conclusion: Cogito, ergo sum—I think, therefore I am.
But here’s the problem—while Descartes had proven his own existence, he had reasoned away the rest of reality. If all he could be sure of was his own mind, then how could he trust that the world around him was real? To solve this, he brought God into the picture.
Descartes argued that the idea of God is innate in all human beings. He believed that God, by definition, must be perfect. And here’s where Descartes makes his leap: because God is perfect, he would not deceive us. That means the external world, the one we see, hear, and touch, must be real—it is not just an illusion or a dream. With this argument, Descartes restores this trust in reality, though some critics argue that his logic is circular. Nonetheless, his ideas laid the groundwork for philosophy and rationalist thought.