From the Supreme Court case Graham v. John Deere Co. (1966):
[Jefferson believed] [t]he patent monopoly was not designed to secure to the inventor his natural right in his discoveries. Rather, it was a reward, an inducement, to bring forth new knowledge. The grant of an exclusive right to an invention was the creation of society—at odds with the inherent free nature of disclosed ideas—and was not to be freely given.
While Jefferson’s earlier views favored patents (“the benefit even of limited monopolies is too doubtful to be opposed to that of their general suppression”),
His views ripened, however, and in another letter to Madison (Aug. 1789) after the drafting of the Bill of Rights, Jefferson stated that he would have been pleased by an express provision in this form:
“Art. 9. Monopolies may be allowed to persons for their own productions in literature & their own inventions in the arts, for a term not exceeding – years but for no longer term & no other purpose.” Id., at 113.
Too bad this language did not make it into the Constitution. This would have capped the copyright term to some finite number, so that Disney could not have it extended all the way to over 100 years now.