The most important part of the argument is that unless we know "something" for certain, then we cannot know "anything". The interest lies in the way great philosophers have tried to solve this problem. Some, like Descartes, retreat into the mind: "I think, therefore I am." Others, such as the British empiricists John Locke and David Hume, would rely on our sense perception. Certain kinds of knowledge may be especially vulnerable to skepticism. For example, an agnostic believes people cannot get knowledge about supernatural things. 