This book is about the conceptual foundations of an intermediate way between liberalism and socialism. From a standpoint of economic theory, this middle way is conceived of as a synthesis of classical (Ricardian) and Keynesian political economy. While the former deals with proportions between individuals or collectives and society in tackling the problems of distribution and value on the basis of the surplus principle, the latter is concerned with the scale of economic activity as explained by the principle of effective demand. Political economy pictures the economic aspects of the functioning of the institutional system within which the behaviour of individuals is embedded. The economy considered is, primarily, neither a market nor a planned economy, but, rather, a monetary production economy. To establish an alternative to liberalism and socialism requires setting up a system of the social sciences. In this work suggestions are made for linking political economy with other social sciences, i.e. sociology, law and politics in the traditional sense, thus establishing the unity of the social sciences. In a Keynesian vein, the social sciences are conceived of as moral sciences, a view which gives rise to a specific philosophy of history. To complete the picture, issues of method associated with the theory of knowledge in the social sciences and the problem of linking theory with historical reality are also covered.