In writing his classic study of the Peloponnesian War, Thucydides sought “an exact knowledge of the past as an aid to the interpretation of the future, which in the course of human things it must resemble if it does not reflect it” (I.22). For twentieth-century British and American realists, e.g., Wight (1978: 24) and Morgenthau (1978: 8–9, 38), this has typically meant seeking supreme, timeless or even eternal truths – perhaps even expressible as mathematical laws – about the state's eternal, self-interested search for power and the need to balance against it. Werner Jaeger's reference to “This political necessity, the mere mathematics of-power politics” conveyed a similar realist message to the German-speaking world of the 1930s; indeed, in a book widely renowned for its penetrating and inspirational account of Greek civic culture, Jaeger asserts that this “necessity” “is defined [by Thucydides] as the true cause … of the war” (Jaeger 1976: 488, my emphasis).

Would not any other social scientist in our own century, if desirous of emulating the increasingly universal validity of the natural sciences and committed to building up reliable knowledge grounded in the deductive certainty of axiomatic formal argument and the “positive” evidence of our senses, also want to claim to “have written my work, not as an essay which is to win the applause of the moment, but as a possession for all time”?