Full Idea
One may acquire a permanent bequeathable property right in a previously unowned thing, as long as the position of others no longer at liberty to use the thing is not thereby worsened.
Gist of Idea
Unowned things may be permanently acquired, if it doesn't worsen the position of other people
Source
Robert Nozick (Anarchy,State, and Utopia [1974], p.178), quoted by G.A. Cohen - Are Freedom and Equality Compatible? 2
Book Reference
'Contemporary Political Philosophy (2nd ed)', ed/tr. Goodin,RE/Pettit,P [Blackwell 2006], p.418
A Reaction
Cohen attacks this vigorously. His main point is that Nozick has a very narrow view of what the acquisition should be compared with. There are many alternatives. Does being made unable to improve something 'worsen' a person's condition?