Skepticism gives a pessimistic reply to questions on whether we really know the things we think we know, and whether our beliefs are reasonable. The theoretical and practical difficulties presented by the skeptical challenge--in that the skeptical life cannot be lived, and the doctrine seems self-defeating--are in fact superficial, according to Ruth Weintraub. Her study looks at several famous skeptical arguments of Descartes, Hume, and the ancient Greek skeptic, Sextus Empiricus. She argues that by drawing on philosophy, rather than science, the skeptical challenge can be answered.