Alfred Marshall’s social philosophy provided the foundations, and also the basic content, of the science set out in his Principles of Economics (1890).  In the pages of John Stuart Mill’s Principles of Political Economy (1848), by contrast, social philosophy had been fused with economic doctrines in order to derive practical interpretations.  Behind these two different formulations stands in the first instance Marshall’s various transformations of Mill’s political economy.  But these scientific transformations were themselves very much the product of his construction of an alternative social philosophy.  In this talk I will briefly survey the three stages by means of which Marshall constructed his distinctive social philosophy.  Before he was particularly interested in political economy he had already concluded that Mill’s associationist psychology must be supplemented with a Coleridgean idea of self-consciousness.  Just after making political economy his primary research interest, Marshall connected this idea of self-consciousness with Hegel’s notion of freedom, and in doing so was able to derive from Hegel’s Philosophy of History an account of the preconditions of modern economic activity.  Here Marshall argued that the subjective and objective grounds of economic activity had come into being by the Middle Ages.  The third stage of Marshall’s construction of a social philosophy occurred when, a few years later, he attempted to use Hegel’s terminology in order to construct a philosophy of modern history.  Modern history, Marshall decided, was the product of a dialectical relationship between individualism and collectivism, which was itself advanced by way of the development of both self-consciousness and physical organization.  From this social philosophy of modern life, Marshall derived the spiritual foundations and the physical content of economic science.