Generally speaking the advanced capital is converted into productive capital, i.e., it assumes the form of elements of production which are themselves the products of past labour. (Among them labour-power.) Capital can function in the process of production only in this form. Now, if instead of labour-power itself, into which the variable part of capital has been converted, we take the labourer's means of subsistence, it is evident that these means as such do not differ, so far as the formation of value is oncerned, from the other elements of productive capital, from the raw materials and the food of the labouring cattle, on which ground Smith in one of the passages quoted above places them, after the manner of the physiocrats, on the same level. The means of subsistence cannot themselves expand their own value or add any surplus-value to it. Their value, like that of the other elements of the productive capital, can re-appear only in the value of the product. They cannot add any more to its value than they have themselves.
Like raw materials, semi-finished goods, etc., they differ from fixed capital composed of instruments of labour only in that they are entirely consumed in the product (at least as far as concerns the capitalist who pays for them) in the formation of which they participate and that therefore their value must be re-placed as a whole, while in the case of the fixed capital this takes place only gradually, piecemeal. The part of productive capital advanced in labour-power (or in the labourer's means of subsistence) differs here only materially and not in respect of the process of labour and production of surplus-value from the other material elements of productive capital.
It differs only in so far as it falls into the category of circulating capital together with one part of the objective creators of the product ("materials" Adam Smith calls them generally), as opposed to the other part of these objective product creators, which belong in the category of fixed capital.