In the previous chapter, we saw that when worn-out constant capital is replaced, or as Marx insists produced anew, during the process of production, the rate of surplus value will always be greater, and usually very much greater, than the rate of profit. If we accept that the rate of surplus value is an exact measure of the degree of exploitation of labour, it would seem to follow that Marx is claiming that the degree of exploitation of labour is likely to be very much greater than its apparent measure; the rate of profit. It therefore comes as something of a shock to discover that while Marx equates the rate of surplus value with the degree of exploitation of labour, and does in fact expect the degree of exploitation to be greater than its apparent level, he also claims that the labourer is paid the full value of his or her labour-power when he or she is paid the bare minimum, or subsistence, cost of reproducing him- or herself. How then is this paradox to be resolved?

The apparent contradiction between these two claims has to do with the very important distinction Marx makes between two quite separate concepts: labour (the amount of work that one may perform in a given time, e.g. during one day), and labour-power (one’s capacity or ability to work).