3. _The money market in which short-time loans are made is peculiar in that the money frequently is borrowed to pay debts, not for investment._ In beginning the discussion of interest, it always is remarked that it is not money, but capital, that is borrowed and loaned. This caution against the superficial errors that so easily beset the popular discussion of interest is much needed, but it is well to note a peculiar case which is apparently in contradiction to this statement. The usual method by which money is loaned in the great industrial centers is called discount, which is the exchange of a certain sum of money for a note or other credit paper of a larger amount, the interest thus being taken out in advance. Much borrowing in the form of discount is for the same purpose as other borrowing--to acquire control of more productive agents, to embark on new enterprises. The peculiarity of the discount money-market is that an unusual number of loans are made to meet contracts that have already been made. There is always a great mass of outstanding obligations, and merchants are compelled to renew these loans on penalty of bankruptcy. This market for short-time loans is not connected closely with the general market for loanable capital. When the need is for ready money, other concrete capital cannot flow in to meet it. This special money demand, therefore, in time of greater or less stress, may fluctuate rapidly, and the interest rate be temporarily higher or lower than the rate on long-time loans. This case is similar to that where two markets, as a retail and a wholesale one, exist side by side, but slowly exerting a mutual influence. [Sidenote: Productive borrowers seek a profit on their investments] 4. _In the long-time money loan the money generally is borrowed first merely as a medium of exchange to get control of indirect agents._ The borrower of a long-time money loan for productive purposes is always seeking to gain by investing the money in wealth that will yield an income larger than the interest he must pay. The borrower, therefore, invests in view of the rate of interest, of the market price of the goods in which he plans to invest, and of the probable chances for earning profits in the business. This case, where certain goods whose price is known are approximately selected before the money is borrowed for investment, is the type of loan to be kept most usually in mind in economic discussion.