Interest

If the Native American tribe that accepted goods worth 60 guilders for the sale of Manhattan in 1626 had invested the money in a Dutch bank at 6.5% interest, compounded annually, then in 2005 their investment would be worth over €700 billion (around USD $1,000 billion), more than the assessed value of the real estate in all five boroughs of New York City. With a 6.0% interest however, the value of their investment today would have been €100 billion (7 times less!).

Compound interest was once regarded as the worst kind of usury, and was severely condemned by Roman law, as well as the common laws of many other countries. ^[2]

Richard Witt's book Arithmeticall Questions, published in 1613, was a landmark in the history of compound interest. It was wholly devoted to the subject (previously called anatocism), whereas previous writers had usually treated compound interest briefly in just one chapter in a mathematical textbook. Witt's book gave tables based on 10% (the then maximum rate of interest allowable on loans) and on other rates for different purposes, such as the valuation of property leases. Witt was a London mathematical practitioner and his book is notable for its clarity of expression, depth of insight and accuracy of calculation, with 124 worked examples.^[3][4]

The Qur'an, revealed over 1400 years ago, explicitly mentions compound interest as a great sin. Interest known in Arabic as riba is considered wrong: "Oh you who believe, you shall not take riba, compounded over and over. Observe God, that you may succeed. (Qur'an 3:130)"

Usury (pronounced /ˈjuːʒəri/, comes from the Medieval Latin usuria, "interest" or "excessive interest", from the Latin usura "interest") originally meant the charging of interest on loans. This would have included charging a fee for the use of money, such as at a bureau de change. After countries legislated to limit the rate of interest on loans, usury came to mean the interest above the lawful rate. In common usage today, the word means the charging of unreasonable or relatively high rates of interest. As such, the term is largely derived from Abrahamic religious principles and Riba is the corresponding Islamic term. The primary focus in this article is on the Christian tradition.

The pivotal change in the English-speaking world seems to have come with the permission to charge interest on lent money: particularly the Act 'In restraint of usury' of Henry VIII in England in 1545 (see book references).