From Das Kapital (1867):
Capital is money, capital is commodities. … In truth, however, value is here the active factor in a process, in which, while constantly assuming the form in turn of money and commodities, it at the same time changes in magnitude, differentiates itself by throwing off surplus value from itself; the original value, in other words, expands spontaneously. For the movement, in the course of which it adds surplus value, is its own movement, its expansion, therefore, is automatic expansion. Because it is value, it has acquired the occult quality of being able to add value to itself. It brings forth living offspring, or, at the least, lays golden eggs."
