Descartes's Method of Universal Doubt in the First Meditation Descartes is widely regarded as the father of modern philosophy. In the First Meditation, he begins with his method of doubt, calling into doubt everything which can be called into question.

In the beginning of the First Meditation, Descartes tries to call all his empirical beliefs into doubt with a single stroke: “I have occasionally caught the senses deceiving me,” he writes, “and it’s prudent never completely to trust who have cheated us even once”. The reason why Descartes began by bringing into doubt all the beliefs that come to us from the senses is to show that science rested on firm foundations and that these foundations lay in the mind and not the senses. He is not aimed to prove that nothing exists or that it is impossible for us to know if anything exists, but to show that all our knowledge of these things through the senses is open to doubt. We could not even be sure that anything outside of us existed, if our scientific knowledge came to us through the senses. Since sense experience is sometimes deceiving, it is obvious to Descartes that a posteriori claim cannot be the basis for claims of knowledge. We do not know that what we experience through our senses is true; at least, we are not certain of it. And we cannot tell when our senses are correctly reporting the way things really are and when they are not. So the best thing to do is to doubt whether any knowledge can be based on our sense experiences.

Then Descartes goes on looking for a further ground for doubt. He thinks that God would be powerful enough to cause all of his sense experiences and mathematical reasoning to be false. He's not assuming that God does exist; he's just saying that, as he understands the concept of God, this would be something that God could do if he existed. In Descartes’s deceiving God argument, he