as is drawn out by Adam Smith in the tenth chapter of the first book of the _Wealth of Nations_.[585] Disagreeableness, difficulty, inconstancy, responsibility, risk of failure, are so many disabilities, for each of which a compensation must be made to the workman in the scale of his wages, as adding in effect so many more hours’ labour; and each higher class of workman must be paid the unit of common labourer’s wages, with the compensations superadded. In practice this means that men will not be found in sufficient numbers to do the higher class work unless the wages are sufficient to make it worth their while to undergo the disabilities. It is assumed that this scale has been adjusted by custom and the “higgling of the market” from generation to generation, till in any given neighbourhood each of the several skilled trades has a definitely recognized place in the series.[586] This reasoning seems less convincing when we consider that the translation of skill into terms of hours would be different in different localities, and that the common labour, which is the unit, would vary in the same way. The measure of value would hold only for a given place, time, and people. To escape from the difficulty, we must consider the difference between the common labour at one time and place and the common labour at another as itself measurable, and allow for it; or else we must consider it as too small to disturb our conclusions, and so neglect it altogether. To reduce common labour to its theoretically simplest terms is to reduce it to something below our experience; and to reduce it to its actually simplest in the given cases is to reduce it to one thing in England, a second in France, a third in India, a fourth in America. There are differences of quality which cannot be with any certainty resolved into differences of quantity; such are the differences of individuals, the differences of nations, the differences of races. It will be found, also, that the part played by common as opposed to skilled labour, and by agricultural as opposed to manufacturing labour, differs so much between country and country that, in order to use labour as a measure, we should need other measures in addition to it. In short, if we had data enough to apply this measure, we should have data enough to dispense with it. It was possibly the force of these considerations that led Malthus, as time went on, to approach somewhat nearer to Ricardo, whose measure, so far as he had one, was not the labour purchased but the labour that entered into cost. But he adhered to the substance of his doctrine as expressed in the tract; and his positions, in detail, were as follows:—