 Immanuel Kant’s work on property is more formal and abstract than Locke’s and—at least until recently-it was less well-known. (But now see Byrd and Hruschka 2006 and Ripstein 2009.) Kant began by emphasizing a general connection between property and agency, maintaining that there would be an affront to agency and thus to human personality, if some system were not arrived at which could permit useful objects to be used. He inferred from this that ‘it is a duty of right to act towards others so that what is external (usable) could also become someone’s’ (Kant 1991 [1797], p. 74) Though this legitimated unilateral appropriation, it did so only in a provisional way. Since the appropriation of a resource as private property affects everyone else’s position (imposing duties on them that they would otherwise not have), it cannot acquire full legitimacy by unilateral action: it must be ratified by an arrangement which respects everyone’s interests in this matter. So the force of the principle requiring people to act so that external objects can be used as property also requires them to enter into a civil constitution, which will actually settle who is to be the owner of what on a basis that is fair to all.