Capital Vol II, p185.

Capital may continually circulate, and that circulation is the responsibility of the capitalist, who may then appear as the producer of profit, but it only circulates for one purpose, its self-valorization, or the production of profit. Otherwise, it would not circulate at all. Marx writes,

“Capital, as self-valorizing value, does not just comprise class relations, a definite social character that depends on the existence of labour as wage-labour. It is a movement, a circulatory process through different stages, which itself in turn includes three different forms of the circulatory process. (money capital, production capital, commodity capital – JA) Hence it can only be grasped as a movement, and not as a static thing…it is clear, however, that despite all revolutions in value, capitalist production can exist and continue to exist only so long as the capital value is valorized…The movements of capital appear as actions of the individual industrial capitalist in so far as he functions as buyer of commodities and labour, seller of commodities and productive capitalist and thus mediates the circuit by his own activity.” ( Capital Volume II, p 185, Penguin Classics edition).