Arthur Cecil Pigou founded welfare economics by synthesizing Marshall's theoretical framework and Sidgwick's categories of market failure and imperfections. His view of welfare economics was expansive, including resource allocation, income redistribution, business cycles, and unemployment. Pigou made important contributions to other areas of economics as well: the theory of value, public finance, index numbers, and evaluation of real national income. The most neglected aspect of Pigou's work is his investigation of a remarkable range of labour-market phenomena explored by subsequent economists – implicit contracts, internal labour markets, wage rigidity, labour market segmentation, human capital theory, and collective bargaining.