Marx argues extensively that 'wages' are the amount required to reproduce the worker, and that capitalist exploitation is the difference between the value created by the worker and the value (wage) needed to reproduce the worker. This reproduction includes the usual suspects; housing, clothing, food, kids^[reproducing a constant supply of future workers as well as supplement reproductive labor], etc -- but also learning and practice^[Marx describes this as intensifying labor-power] that are required to perform that job, like a Doctor or a Nuclear engineer. At the same time, if the wages dip below the necessary reproductive cost it degrades the worker's ability to work. Marx even points out that if workers didn't require a wage (and thus could reproduce themselves freely) they would also never need to work!^[John Stewart Mill: "If labour could be had without purchase, wages might be dispensed with." Karl Marx: "But if the labourers could live on air they could not be bought at any price. The zero of their cost is therefore a limit in a mathematical sense, always beyond reach..." Capital v1c24s4]