The value of labour-power is determined, as in the case of every
 other commodity, by the labour-time necessary for the production, and consequently
 also the reproduction, of this special article. So far as it has value,
 it represents no more than a definite quantity of the average labour of
 society incorporated in it. Labour-power exists only as a capacity, or
 power of the living individual. Its production consequently pre-supposes
 his existence. Given the individual, the production of labour-power consists
 in his reproduction of himself or his maintenance. For his maintenance
 he requires a given quantity of the means of subsistence. Therefore the
 labour-time requisite for the production of labour-power reduces itself
 to that necessary for the production of those means of subsistence; in
 other words, the value of labour-power is the value of the means of subsistence
 necessary for the maintenance of the labourer. Labour-power, however, becomes
 a reality only by its exercise; it sets itself in action only by working.
 But thereby a definite quantity of human muscle, nerve, brain, &c.,
 is wasted, and these require to be restored. 168This increased
 expenditure demands a larger income. [6] If the owner
 of labour-power works to-day, to-morrow he must again be able to repeat
 the same process in the same conditions as regards health and strength.
 His means of subsistence must therefore be sufficient to maintain him in
 his normal state as a labouring individual. His natural wants, such as
 food, clothing, fuel, and housing, vary according to the climatic and other
 physical conditions of his country. On the other hand, the number and extent
 of his so-called necessary wants, as also the modes of satisfying them,
 are themselves the product of historical development, and depend therefore
 to a great extent on the degree of civilisation of a country, more particularly
 on the conditions under which, and consequently on the habits and degree
 of comfort in which, the class of free labourers has been formed. [7]
 In contradistinction therefore to the case of other commodities, there
 enters into the determination of the value of labour-power a historical
 and moral element. Nevertheless, in a given country, at a given period,
 the average quantity of the means of subsistence necessary for the labourer
 is practically known.