Interest is comparatively a new word in the language meaning also a premium for a loan of money. It first appeared in the fourteenth century, as a substitute for usury, in the first law ever enacted by a Christian nation that permitted the taking of a premium for any loan. The word usury was very odious to the Christian mind and conscience.
Interest was at the first a legal term, used in law only, and it has always been applied to that premium or measure of increase that is permitted or made legal by civil law.
In modern usage usury is limited in its meaning to that measure of increase prohibited by the civil law. Thus the two words interest and usury now express what was formerly expressed by the one word usury alone. Interest covers that measure of increase that is authorized in different countries, while usury, with all the odium that has been attached to it for ages, is limited to that measure of increase that for public welfare is forbidden by the laws of a state.
The distinction is wholly civic and legal. That may be usury in one state which is only interest in another. The legal rates greatly vary and are changed from time to time in the states themselves. If a state should forbid the taking of any increase on loans, then all increase would be usury, and there could be no interest; or if a state should repeal all laws limiting the exactions of increase, then there would be no usury in that state. Usury is increase forbidden by civil law. Separated from the enacted statutes of a state the distinction disappears. There is no moral nor is there an economic difference.
Blackstone says: "When money is lent on a contract to receive not only the principal sum again, but also an increase by way of compensation for the use, the increase is called interest by those who think it lawful, and usury by those who do not."
The moral nature of an act does not depend on the enacted statutes of human legislators, and the laws of economics are eternal. We must not permit our views of divine and economic truth to be perverted by this modern division of increase into legal and illegal. In order that the whole truth may be now expressed in our language we must combine with the old word usury the new word interest; then only will we have the full force of the revealed truth. "Wherefore then gavest not thou my money into the bank, that at my coming I might have required mine own with usury or interest?" It is rendered interest in the Revised Version.
Throughout this discussion usury is used in its full old classical meaning for any increase of a loan, great or small, whether authorized or forbidden by the civil state.