Gradually, a science policy arose that ideas be as free as the air (air being a free good, not just a public good). Steven Johnson, in The invention of air (a 2008 book on Enlightenment Europe and America, especially on Joseph Priestley) quotes Jefferson: "That ideas should spread freely from one to another over the globe, for the moral and mutual instruction of man, and improvement of his condition, ... like the air ... incapable of confinement or exclusive appropriation." [11]