CHANGE IS TAKING PLACE in all human societies all the time. Sometimes it is sudden and catastrophic, as when a system of government is destroyed by revolution and replaced by a different one; sometimes it is gradual and hardly perceptible, so that even the members of the society themselves scarcely notice it. But it is always there, and social anthropologists who wish to understand the working of the societies they study must take account of it. Here, in particular, they must play the historian; changes take place in time, and they can only be understood as causal sequences of events leading up to new states of affairs. And it is these new states of affairs, ‘the present’, that the social anthropologist is trying to understand. He is a historian, but he is so only in a particular context and for a particular purpose.