"Whoever derives his revenue from a fund which is his own, must draw it either from his labor, from his stock, or from his land. The revenue derived from labor is called wages. That derived from stock, by the person who manages or employs it, is called profit. That derived from it by the person who does not employ it himself, but lends it to another, is called the interest (f)or the use of money (or stock). It is the compensation which the borrower pays to the lender, for the profit which he has an opportunity of making by the use of the money (or stock). Part of that profit naturally belongs to the borrower, who runs the risk and takes the trouble of employing it; and part to the lender, who affords him the opportunity of making this profit. The interest of money is always a derivative revenue, which, if it is not paid from the profit which is made by the use of the money, must be paid from some other source of revenue, unless perhaps the borrower is a spendthrift, who contracts a second debt in order to pay the interest of the first." (Smith)