The obligation to restore the property of another to its owner

Having explained, so far as our purpose requires, the right which belongs to us over persons or over things, we must see also what obligation in consequence rests upon us. Such obligation, moreover, arises either from things which exist or from things which do not exist. Under the term things, I shall now include persons, so far as may be convenient for us.

From things which exist, there arises the obligation by which a person, who has property of mine in his possession, is bound to do what he can to restore it to my control. He is bound, I say, to do what he can; for there is no obligation to do what is impossible, or even to return the property at his own expense. The possessor is, however, under obligation to make the possession known, in order that the other may recover his own. Just as, in the state of community ownership, a certain equality had to be observed, that one might have the use of the common property as well as another, so after the introduction of property ownership, a kind of mutual arrangement was entered into between owners, that one who had another's property in his possession should restore it to the owner. If, in fact, the force of ownership had been limited to this, that property should be restored to the owner only on demand, the right of ownership would have been too weak, and the protection of property too expensive.