The Method of Doubt

Rene Descartes wanted to find something — anything — that was absolutely certain. His method: doubt everything that can possibly be doubted. Your senses can deceive you (optical illusions, dreams). Mathematics might be wrong if an evil demon is manipulating your mind.

Descartes was not a skeptic. He used doubt as a tool to find certainty. Strip away everything questionable and see what remains. It is like removing all unstable ground to find bedrock — whatever still stands is something you can build on.