Philosophy, it has often been said, begins with wonder. For the first thinkers in the Western philosophical tradition, Thales and his early Greek colleagues, it was wonder about the world. It moved them to inquire into the origin and nature of things around them and to offer, instead of mytho-poetic accounts of phenomena that appealed to gods and mystifying powers, natural explanations drawn from experience. At a certain point, however – and this is true whether what is at issue is the historical development of philosophy as a discipline or the intellectual development of an individual philosopher – wonder turns inward and philosophy becomes a very personal affair. Questions about the heavens and the earth, about objects and forces in nature, both visible and hidden, give way to questions about the self and about the life one is leading. It was Socrates, we are told, who first turned philosophy from a search for nature's causes and ultimate constituents to an inquiry into how to be good and achieve well-being.