This was the concept of normal value; that is, the average or medium amount of utility attributed to goods in the average conditions of life and exchange. On the one hand, it avoided the excesses and the arbitrariness of individual estimates; on the other hand, it did not attribute to value the characters of immutability and rigidity. Contrary to the assumptions of some modern writers, the Schoolmen never said that value was something as fixedly inherent in goods as physical and chemical qualities. When they spoke of "intrinsic" value, they had in mind merely the constant capacity of certain commodities to satisfy human wants. Even to-day bread has always the intrinsic potency of alleviating hunger, regardless of all the fluctuations of human appraisement. The objectivity that the mediæval writers ascribed to value was relative. It assumed normal conditions as against exceptional conditions. To say that value was objective merely meant that it was not wholly determined by the interplay of supply and demand, but was based upon the stable and universally recognised use-qualities of commodities in a society where desires, needs, and tastes were simple and fairly constant from one generation to another. How or where was this relatively objective value of goods to find concrete expression? In the "communis aestimatio," or social estimate, declared the canonists. Objective value and just price would be ascertained practically through the judgment of upright and competent men, or preferably through legally fixed prices. But neither the social estimate nor the ordinances of lawmakers were authorised to determine values and prices arbitrarily. They were obliged to take into account certain objective factors. In the thirteenth and fourteenth centuries, the factors universally recognised as determinative were the utility or use-qualities of goods, but especially their cost of production. Later on, in the sixteenth and seventeenth centuries, risk and scarcity were given considerable prominence as value determinants. Now cost of production in the Middle Ages was mainly labour cost; hence the standard of value was chiefly a labour standard. Moreover, this labour doctrine of true value and equality in exchanges was strongly reinforced by another mediæval principle, according to which labour was the supreme if not the only just title to rewards.