"By a perpetual monopoly, all the other subjects of the state are taxed very absurdly in two different ways: first, by the high price of goods, which, in the case of a free trade they could buy much cheaper; and secondly, by their total exclusion from a branch of business which it might be both convenient and profitable for many of them to carry on. It is for the most worthless of all purposes, too, that they are taxed in this manner. It is merely to enable the company to support the negligence, profusion, and malversation of their own servants."

--Adam Smith (1723-1790), An Inquiry into the Nature and Causes of the Wealth of Nations, Book 5, Chapter 1, Part 3, Article 1. (Britannica Edition, Chicago, 1952, pp. 329-330.)

Smith is not saying that only perpetual monopolies have ill effects. He is saying essentially what Lord Macaulay said two generations after Adam Smith's time: that the good that a monopoly does, if it happen at all, is done reasonably soon after the grant is made, while the bad that a monopoly does is made worse as the term increases. Hence Smith's objection to "perpetual" monopolies is in fact an objection against monopolies that are so long that they outlive the good reasons for their existence. This objection would not be satisfied by Jack Valenti's and Mary Bono's proposal to make copyright last "forever less one day."

T.