If nature has made any one thing less susceptible than all others of exclusive property, it is the action of the thinking power called an idea which an individual may exclusively possess as long as he keeps it to himself; but the moment it is divulged, it forces itself into the possession of everyone, and the receiver cannot dispossess himself of it. Its peculiar character, too, is that no one possesses the less, because every other possesses the whole of it. He who receives an idea from me, receives instruction himself without lessening mine; as he who lights his taper at mine, receives light without darkening me. That ideas should freely spread from one to another over the globe, for the moral and mutual instruction of man and improvement of his condition, seems to have been peculiarly and benevolently designed by nature when she made them, like fire, expansible over all space, without lessening their density in any point; and like the air in which we breathe, move, and have our physical being, incapable of confinement or exclusive appropriation. Inventions then cannot, in nature, be a subject of property.
— Thomas Jefferson in a letter to Isaac McPherson written from Monticello on August 13, 1813. Available in The Writings of Thomas Jefferson: being his autobiography, correspondence, reports, messages, addresses, and other writings, official and private. Published by the order of the Joint Committee of Congress on the Library, from the original manuscripts, deposited in the Department of State, Volume 6, p. 180. Letter begins on page 175. Cited by John Perry Barlow as the introduction to his essay “The Economy of Ideas: A Framework for Rethinking Patents and Intellectual Property in the Digital Age”, available in Wired, Issue 2.03, March 1994.
"If nature has made any one thing"