The idea that human history is marked by certain "discontinuities' and does not have a smoothy developing form is of course a familiar one and has been stressed in most versions of Marxism. My use of the term has no particular connection with historical materialism, however, and is not directed at characterising human history as a whole. There undoubtedly are discontinuities at various phases of historical development — as, for example, at the points of transition between tribal societies and the emergence of agrarian states. I am not concerned with these. I wish instead to accentuate that particular discontinuity, or set of discontinuities, associated with the modern period.