Liberty rights and claim rights are the inverse of one another: a person has a liberty right permitting him to do something only if there is no other person who has a claim right forbidding him from doing so; and likewise, if a person has a claim right against someone else, that other person's liberty is thus limited. This is because the deontic concepts of obligation and permission are De Morgan dual; a person is permitted to do all and only the things he is not obliged to refrain from, and obliged to do all and only the things he is not permitted to refrain from.