How was labour cost to be measured, and the different kinds of labour evaluated? By the necessary and customary expenditures of the class to which the labourer belonged. Mediæval society was composed of a few definite, easily recognised, and relatively fixed orders or grades, each of which had its own function in the social hierarchy, its own standard of living, and its moral right to a livelihood in accordance with that standard. Like the members of the other orders, the labourers were conceived as entitled to live in conformity with their customary class-requirements. From this it followed that the needs of the labourer became the main determinant of the cost of production, and of the value and just price of goods. Inasmuch as the standards of living of the various divisions of the workers were fixed by custom, and limited by the restricted possibilities of the time, they afforded a fairly definite measure of value and price,--much more definite than the standard of general utility. To Langenstein, vice chancellor of the University of Paris in the latter half of the fourteenth century, the matter seemed quite simple; for he declared that every one could determine for himself the just price of his wares by referring to the customary needs of his rank of life.[221] Nevertheless, class needs are not and cannot be a standard of exchange-equivalence. They cannot become a criterion of equality, a common denominator, a third term of comparison, between labour and wages. When we say that a given amount of wages is equal to a given content of livelihood, we express a purely economic, positive, and mathematical relation: when we say that a given amount of labour is equal to a given content of livelihood, we are either talking nonsense or expressing a purely ethical relation; that is, declaring that this labour _ought to_ equal this livelihood. In other words, we are introducing a fourth term of comparison; namely, the moral worth or personal dignity of the labourer. Thus, we have not a single and common standard to measure both labour and wages, and to indicate a relation of equality between them. While class needs directly measure wages, they do not measure labour, either quantitatively, or qualitatively, or under any other aspect or category. Aside from this purely theoretical defect, the canonist doctrine of wage justice was fairly satisfactory as applied to the conditions of the Middle Ages. It assured to the labourer of that day a certain rude comfort, and probably as large a proportion of the product of industry as was practically attainable. Nevertheless it is not a universally valid criterion of justice in the matter of wages; for it makes no provision for those labourers who deserve a wage in excess of the cost of living of their class; nor does it furnish a principle by which a whole class of workers can justify their advance to a higher standard of living. It is not sufficiently elastic and dynamic.