The Wealth of Nations by Part 2 Chapter 4 Page 20

In some countries the interest of money has been prohibited by law. But as something can everywhere be made by the use of money, something ought everywhere to be paid for the use of it. This regulation, instead of preventing, has been found from experience to increase the evil of usury; the debtor being obliged to pay, not only for the use of the money, but for the risk which his creditor runs by accepting a compensation for that use.

He is obliged, if one may say so, to insure his creditor from the penalties of usury.

In countries where interest is permitted, the law, in order to prevent the extortion of usury, generally fixes the highest rate which can be taken without incurring a penalty. This rate ought always to be somewhat above the lowest market price, or the price which is