He contends that the amount of product added by the presence of the least productive labourer in a group or establishment describes the productivity of that and every other labourer for whom the man in question can be substituted. Nevertheless this marginal labourer had the use of _some_ capital, no matter how little or how poor; consequently the increment of product which follows his activity is partly due to capital. It represents something other than his own productive power. If his wage equals the value of this increment of product, he is receiving something more than his specific product. In the second place, Professor Clark maintains that the difference between what a labourer produces when he uses the whole of a certain supply of capital and what he produces when he has shared that capital with another labourer, represents the specific productivity of the relinquished capital. Let us assume that in a given case the difference is ten units of product. When the first man had the whole capital to himself, the product was one hundred units; when he shares the use of it with another, the total product is one hundred and eighty units. As the two men are assumed to be equally productive, each has to his credit ninety units of product. Working with half the capital, the first man finds that the resulting product is ten units less than when he was using the whole capital. Hence these ten units represent the portion that the relinquished capital contributed to the product; and if the productivity of half the capital is ten units, that of the whole capital must be twenty units. Nevertheless, the ten units by which the product was enlarged when the man had the whole capital, did not come into being without his co-operation; hence they cannot be entirely attributed to the one-half share of the capital. In other words, the productivity of the relinquished capital seems to be less than ten units. It also seems to be more than ten units; for we may assume that if each man were to use one-half the capital independently of the other, the resulting total product would be less than one hundred and eighty units, or less than ninety units for each. Consequently the difference between the product resulting from the first man's use of the whole capital and that resulting from his use of half the capital would be more than ten units; and this difference is specifically attributable to half the capital. Who can say which of these calculations is correct, or whether either of them is correct?