 Philosophy, then, is the study of the ‘thought-spectacles’ through which we view the world; and since at least some of these change over time, at least some philosophy is necessarily historical. Because these categories are so important to every aspect of our experience, philosophy – even if it is always tentative and often seems abstract and esoteric – is a crucially important activity, which responds to the vital, ineradicable human need to describe and explain the world of experience.