How do you know that you exist? What does it mean to have a future? Are you the same thing as your brain? What does it mean to be free? How can you know what knowledge is? A woman was advising her anguished friend, 'Be philosophical - then you won't need to think about it.' Well, being philosophical is sometimes taken to mean that you should adopt a resigned attitude to the world - a quiet-ism - but the study that is western philosophy, starting with the ancient Greeks and continuing today in un...