Everything that the working class consumes in order to restore its labour power, has value. For this reason, the value of articles of consumption and also of expenditure upon training constitute the value of labour power. Different commodities possess different values. In like manner, each kind of labour power has its peculiar value. The labour power of the compositor has one value, the labour power of the unskilled labourer has another.
Let us now return to the factory. The capitalist buys raw materials, fuel, machinery, lubricants, and other necessaries; then he buys labour power, “engages hands.” He pays cash for everything. The work of production begins. The workers work, the wheels turn, the fuel is burned, the lubricant is used, the factory buildings suffer wear and tear, the labour power is expended. As a result, there issues from the factory a new commodity. The commodity, like all commodities, has value. What is this value? First of all, the commodity has absorbed into itself the value of the means of production that have been used up; that which has passed into it — raw materials, fuel consumed, the worn parts of the machinery, and so on. All this has now been transformed into the value of the commodity. In the second place, there has passed into the commodity the labour of the workers. If the workers were 80 in number, and if in the production of the commodity each worked for 30 hours, then there will have been expended in all 900 working hours. The full value of the product will therefore consist of the value of the utilised materials(let us assume that the value of these is equivalent to 600 hours), together with the new value which the workers have added by their labour, namely 900 hours. The total is therefore 600 + 900 = 1,500 working hours.
But how much did the commodity cost the capitalist? For the raw materials he paid in full; that is to say, he paid a sum of money corresponding to the value of 600 working hours. But what did he pay for labour power? Did he pay for the whole 900 hours? Here lies the key