 Aristotle asked one of the most fundamental questions of economics: What is a price? The simple answer is a ratio of two goods, one of which might be the established currency, but he maintained that it made no difference; a price in barter is the same as a money price. However, he qualified this claim with the recognition of the evolution of money over time and the fact that many mistake it as an end in itself rather than simply a means to facilitate barter. More remarkably, Aristotle grasped that a price masks the fact that no two commodities are fully commensurable. Exchange of goods or services, he noted, is grounded in fulfilling specific human needs, and no two of those are ever the same.