We see the present with the eyes of the past, and the past with the eyes of the present. This is a truism: but one that is nonetheless worth repeating at a time when it is fashionable to believe that we live in a posthistoric age, that the past has little to tell us that is new or that is true. But what is fashionable is not correct, for all that we know comes from the past, from some kind of a past; all of our knowledge is essentially past-knowledge, whether we are conscious of this or not. Politics, for example, is not only inseparable from historical interpretation: it is a certain kind of historical interpretation. And since this interpretation is a living and changing thing in our minds (for "history," contrary to the generally accepted view, is not a static account of past periods) the interpretation involves, inevitably, the changing and moving "present": it is part and parcel of the movement of ideas. And the problem of how ideas move nowadays has preoccupied my mind (note the implicit meaning of the word pre-occupy) for a long time.