Whether we think of Money as tangible coin, or only as the Money signs and symbols of account books, Money is not a basic fact in Economics. Mankind cannot live upon Money. It is neither eatable nor wearable. Nor is it shelter. Likewise of Money terms. Money is a secondary Economic factor--a representative of value, whereby the relative desirability of commodities is measured and expressed in trade. It is therefore the comprehensive surface-fact of Economics beneath which the basic facts must be sought. In other phrasing, Money is that secondary category in Economics which comprehends every kind and form of medium for trading commodities in the world-wide process that we descriptively characterize as “mankind making a living.” Mankind being a basic Economic category, and the process of making a living being the Economic human necessity and purpose, Money can have but one comprehensive significance in Economics. Be it in the form of coin, or in the form of paper currency, or in the form of entries in books of account (where it appears only in name and arithmetical denominations), it is the universal medium and Economic measuring rod of exchanges or trade. Whether one makes Money or not depends, as a rule, upon which side of his accounts in ledgers the Money balance appears at final accountings. It is Money in this sense that goes farthest to justify the superficial definition of Economics as the science of making money. We only skim the surface of Economic phenomena, however, by coming to an understanding of the nature and the function of Money. Money is only one of the secondary categories which must be identified and properly related in any thoughtful study of Economic science. Below that financial surface are phenomena which Money merely measures and compares. The first of those underlying phenomena is Trade, for which Money is the medium and upon which our attention must next be concentrated. THIRD LESSON TRADE Trade, for which Money is the Economic medium and Money-terms the Economic language, consists superficially in interchanges of tangible commodities, but essentially in interchanges of human service. Tangible commodities, with a semi-exception as to real estate, are produced by interchanges of human service from the very extreme of the primary production of those commodities to and including their final delivery for ultimate consumption. Real estate, too, is thus produced in so far as it consists of structures, of soil cultivation, of mining mechanisms, of excavations, or of any other kind of artificial alteration.