Law of Variation of Labour, an objective need for the labour functions of the worker to correspond to the level of development of the technical base of social production. The prerequisites for variation of labour are caused by the development of production based on the use of machinery. Marx wrote that largescale industry "is continually causing changes not only in the technical basis of production, but also in the functions of the labourer, and in the social combinations of the labour-process. At the same time, it thereby also revolutionises the division of labour within the society, and incessantly launches masses of capital and of workpeople from one branch of production to another. But ... Modern Industry, by its very nature, therefore necessitates variation of labour, fluency of function, universal mobility of the labourer" (Karl Marx, Capital, Vol. I, p. 457). Capitalist relations of production turn the worker into an appendage of the machine and determine his one-sided development. The anarchy of social production characteristic of capitalism constantly upsets the correspondence between the functions of the labourer and the implements of production used; changes in the technical base of production caused by the development of science and technology are not accompanied by the appearance of social conditions ensuring that worker is trained in keeping with the changing requirements of production. This contradiction becomes especially acute against the background of the scientific and technological revolution, which aggravates this lack of correspondence between the functions of the workers and the continuously changing technical base of capitalist production. Social barriers to variation of labour are eliminated once public ownership of the means of production is established. Socialist society systematically analyses the interrelationships between the production functions of workers and changes in the technical base of production and trains skilled workers and experts in good time. The right to work, as declared by the Constitution of the USSR, includes the right to choose one’s trade or profession, type of job and work in accordance with one’s inclinations, abilities, training and education, due account being taken of the needs of society (see Labour). Under mature socialism, when changes take place in the structure of the productive forces under the impact of the scientific and technological revolution, socialist relations of production constitute an objective foundation for expanding the field of variation of labour. The forms in which the law of variation of labour is manifest are gaining increasingly in importance. These include improvement of skills, the mastering of new jobs, alternation of different types of work, doing more than one job, the release and retraining of workers, the redistribution of the labour force between enterprises, economic sectors, etc. Variation of labour and the related comprehensive development of labourers lead to a rise in the productive potential of social labour in the interests of society and every one of its members.