Two approaches to the theory of international relations at present compete for our attention. The first of these I shall call the classical approach. By this I do not mean the study and criticism of the “classics” of international relations, the writings of Hobbes, Grotius, Kant, and other great thinkers of the past who have turned their attention to international affairs. Such study does indeed exemplify the classical approach, and it provides a method that is particularly fruitful and important. What I have in mind, however, is something much wider than this: the approach to theorizing that derives from philosophy, history, and law, and that is characterized above all by explicit reliance upon the exercise of judgment and by the assumptions that if we confine ourselves to strict standards of verification and proof there is very little of significance that can be said about international relations, that general propositions about this subject must therefore derive from a scientifically imperfect process of perception or intuition, and that these general propositions cannot be accorded anything more than the tentative and inconclusive status appropriate to their doubtful origin.