The method of ascertaining specific productivity which has been described in the last paragraph is thought by Professor Clark to receive confirmation from the fact that it leads to the same conclusion as the first and more direct method; namely, that the specific productivity of labour is expressed in the product of the marginal labourer. As a matter of fact, this conclusion is yielded by both methods; for the specific productivity of the first labourer appeared as eighty units, which was also the specific productivity of the second labourer, who was the marginal labourer. As we saw in the second last paragraph, however, the marginal product is not due to labour alone; hence the verification provided by the second method is in reality a refutation. Apparently the majority of economists do not accept Professor Clark's theory; for of the nine who discussed certain applications of it at the nineteenth annual meeting of the American Economic Association only one approved it, three were non-committal, and five expressed their dissent.[236] Even if the theory were true its hypothetical character would deprive it of any practical value. It assumes a régime of perfect competition, but this assumption is so seldom realised that no rule based upon it can throw much light on the question of the productivity of present day labourers. Even if it were exactly applicable to existing conditions, that is, if labourers were actually getting their specific products, the theory would not provide us with a doctrine of just wages. As we have seen in former chapters, productivity is neither the only nor the highest canon of justice, whether as regards the comparative claims of capital and labour, or as regards the claims of different labourers. The contention that capital ought to command interest because it aids in bringing forth the product, is neither self evident nor demonstrable by any process of reasoning. Even if we should concede that the capitalist has a right to interest by virtue of the productivity of his capital, we should not therefore conclude that this right is as cogent as the corresponding right of the labourer. In the former case the productive agency is not human nor active, but only material and passive; and the recipient of the product performs no labour as capitalist, but is left free to get a livelihood by personal activity. The productivity of labour differs in all these respects, and the difference is ethically sufficient to justify the claim that the labourer may sometimes have a right to a part of the specific product of capital. To sum up the matter in the words of Professor Wicker: "To have proved that the capitalist gets in interest what his capital produces is not to have proved that the capitalist gets what he has earned. To have proved that the landlord gets what his land produces is not to have proved that the landlord earns his distributive share.... Economics is not ethics; explanation is not justification."[237]