Three elements contributed to shift the basis of theories as to the end of law from wills to wants, from a reconciling or harmonizing of wills to a reconciling or harmonizing of wants. The most important part was played by psychology which undermined the foundation of the metaphysical will-philosophy of law. Through the movement for unification of the social sciences, economics also played an important part, especially indirectly through the attempts at economic interpretation of legal history, reinforcing psychology by showing the extent to which law had been shaped by the pressure of economic wants. Also the differentiation of society, involved in industrial organization, was no mean factor, when classes came to exist in which claims to a minimum human existence, under the standards of the given civilization, became more pressing than claims to self-assertion. Attention was turned from the nature of law to its purpose, and a functional attitude, a tendency to measure legal rules and doctrines and institutions by the extent to which they further or achieve the ends for which law exists, began to replace the older method of judging law by criteria drawn from itself. In this respect the thought of the present is more like that of the seventeenth and eighteenth centuries than that of the nineteenth century. French writers have described this phenomenon as a "revival of juridical idealism." But in truth the social utilitarianism of today and the natural-law philosophy of the seventeenth and eighteenth centuries have only this in common: Each has its attention fixed upon phenomena of growth; each seeks to direct and further conscious improvement of the law.