The proposition that skilled work has declined in importance with the rise of capitalist industrialization—most notably during the 20th century and following the rise of the scientific management movement. The most notable proponents of this thesis have been neo-Marxists such as Georges Friedmann and Harry Braverman. The latter argues that private capitalists pursue increased control over their workforces, both as a means of increasing labour productivity by extracting greater profits, and for the political purpose of subduing the working class. The principal means for securing this control is said to be the separation of conception and execution, that is, appropriation of all planning and design knowledge by managers, with the workers being delegated only the responsibility for operating pre-programmed machinery and performing routinized and de-skilled tasks. This process was characterized as the ‘degradation of work’ because it stripped formerly skilled employees (for example craft-workers and clerical workers) both of their skills and their self-respect. The thesis formed the core of the so-called labour process debate that preoccupied neo-Marxist sociologists of work during the 1980s. See also proletarianization.