Another exchange-equivalence theory which turns upon the concept of value is that found in the pages of the mediæval canonists and theologians. But it interprets value in a different sense from that which we have just considered. As the measure of exchange equivalence the mediæval theory takes objective value, or true value. However, the proponents of this view did not formally apply it to wage contracts, nor did they discuss systematically the question of just wages. They were not called upon to do this; for they were not confronted by any considerable class of wage earners. In the country the number of persons who got their living exclusively as employés was extremely small, while in the towns the working class was composed of independent producers who sold their wares instead of their labour.[218] The question of fair compensation for the town workers was, therefore, the question of a fair price for their products. The latter question was discussed by the mediæval writers formally, and in great detail. Things exchanged should have equal values, and commodities should always sell for the equivalent of their values. By what rule was equality to be measured and value determined? Not by the subjective appreciations of the exchangers, for these would sometimes sanction the most flagrant extortion. Were no other help available, the starving man would give all he possessed for a loaf of bread. The unscrupulous speculator could monopolise the supply of foodstuffs, and give them an exorbitantly high value which purchasers would accept and pay for rather than go hungry. Hence we find the mediæval writers seeking a standard of _objective_ value which should attach to the commodity itself, not to the varying opinions of buyers and sellers. In the thirteenth century Albertus Magnus[219] and Thomas Aquinas[220] declared that the proper standard was to be found in labour. A house is worth as many shoes as the labour embodied in the latter is contained in the labour embodied in the former. It is worthy of note that the diagram which Albertus Magnus presents to illustrate this formula of value and exchange had been used centuries before by Aristotle. It is likewise noteworthy that this conception of ethical value bears a striking resemblance to the theory of economic value upheld by Marxian Socialists. However, neither Aristotle nor the Schoolmen asserted that all kinds of labour had equal value. Now this mediæval labour-measure of value could be readily applied only to cases of barter, and even then only when the value of different kinds of labour had already been determined by some other standard. Accordingly we find the mediæval writers expounding and defending a more general interpretation of objective or true value.