Against the foregoing argument it may be objected that the employer does his full duty when he pays the labourer the full value of the product or service. Labour is a commodity of which wages are the price; and the price is just if it is the fair equivalent of the labour. Like any other onerous contract, the sale of labour is governed by the requirements of commutative justice; and these are satisfied when labour is sold for its moral equivalent. What the employer is interested in and pays for, is the labourer's activity. There is no reason why he should take into account such an extrinsic consideration as the labourer's livelihood. Most of these assertions are correct, platitudinously correct, but they yield us no specific guidance because they use language vaguely and even ambiguously. The contention underlying them was adequately refuted in the last chapter, under the heads of theories of value and theories of exchange equivalence. At present it will be sufficient to repeat summarily the following points: if the value of labour is to be understood in a purely economic sense it means market value, which is obviously not a universal measure of justice; if by the value of labour we mean its ethical value we cannot determine it in any particular case merely by comparing labour and compensation; we are compelled to have recourse to some extrinsic ethical principle; such an extrinsic principle is found in the proposition that the personal dignity of the labourer entitles him to a wage adequate to a decent livelihood; therefore, the ethical value of labour is always equivalent to at least a living wage, and the employer is morally bound to give this much remuneration.