Classical political economy explains economic activity in terms of the reproduction and distribution of a surplus produced by labour. This classical framework, which underpins the work of authors from Adam Smith to Karl Marx, was abandoned by orthodox theory after the marginalist revolution. Alfred Marshall, the founder of the Cambridge economic tradition, attempted to provide a view that would unify classical political economy and the marginalist revolution, leading to an approach which was termed as neoclassical economics. However, the marginalist elements of neoclassical economics became increasingly more important than the contributions of the classical political economists, and economics became known as the study of optimising behaviour under scarcity, rather than the study of the reproduction of a surplus, while resorting extensively to mathematical modelling.