community might also benefit. Nonetheless, in times of great necessity, there, all goods become a commons. Luis de Molina argued that individual owners take better care of their goods than is taken of common property, a form of the tragedy of the commons. Money, value, and price The most complete and methodical developments of a Salamancan theory of value were by Martín de Azpilcueta (1493–1586) and Luis de Molina. Interested in the effect of precious metals arriving from the Americas, de Azpilcueta proved that in the countries where precious metals were scarce, prices for them were higher than in those where they were abundant. Precious metals, like any other mercantile good, gained at least some of their value from their scarcity. This scarcity theory of value was a precursor of the quantitative theory of money put forward slightly later by Jean Bodin (1530–1596). Up until that time, the predominant theory of value had been the medieval theory based on the cost of production as the sole determinant of a just price (a variant of the cost-of-production theory of value, most recently manifested in the labor theory of value). Diego de Covarrubias and Luis de Molina developed a subjective theory of value and prices, which asserted that the usefulness of a good varied from person to person, so just prices would arise from mutual decisions in free commerce, barring the distorting effects of monopoly, fraud, or government intervention. Expressing this in today's terms, the adherents of the School defended the free market, where the fair price of a good would be determined by supply and demand. On this Luis Saravia de la Calle wrote in 1544: Those who measure the just price by the labour, costs, and risk incurred by the person who deals in the merchandise or produces it, or by the cost of transport or the expense of traveling...or by what he has to pay the factors for their industry, risk, and labour, are greatly in error.... For the just price arises from the abundance or scarcity of goods, merchants, and money...and not from costs, labour, and risk.... Why should a bale of linen brought overland from Brittany at great expense be worth more than one which is transported cheaply by sea?... Why should a book written out by hand be worth more than one which is printed, when the latter is better though it costs less to produce?...