The Theory of the Leisure Class: An Economic Study of Institutions (1899), by Thorstein Veblen, is a treatise on economics and a detailed, social critique of conspicuous consumption, as a function of social class and of consumerism, derived from the social stratification of people and the division of labour, which are the social institutions of the feudal period (9th – 15th centuries) that have continued to the modern era. Conducted in the late 19th century, Veblen's socio-economic analyses of the emergent division of labour proved to be accurate, sociological predictions of the economic structure of an industrial society.