The generation which followed upon Gossen and Jennings laid the foundations on which economic science .has built ever since. Their names therefore mark the threshold of the present, which it is not for the historian to overstep. Of the four great thinkers who first formulated the theory of marginal utility, two still preserved something of the old idealistic spirit: Walras and Marshall. The attitude of Jevons and Menger, however, was already purely positivistic, or, to use the term which the selflove of devoted disciples has made fashionable, purely scientific. It was the more modem attitude, and th~refore the attitude which won the field. Walras was eclipsed by Pareto, and it is only at Cambridge that the great tradition of Locke and Leibniz still SUIVlves.