Natural and legal rights are two types of rights. Legal rights are those bestowed onto a person by a given legal system. Natural rights are those not contingent upon the laws, customs, or beliefs of any particular culture or government, and therefore universal and inalienable (i.e., cannot be sold, transferred, or removed).The theory of natural law is closely related to the theory of natural rights. During the Age of Enlightenment, natural law theory challenged the divine right of kings, and became an alternative justification for the establishment of a social contract, positive law, and government — and thus legal rights — in the form of classical republicanism.[dubious – discuss][original research?][clarification needed] Conversely, the concept of natural rights is used by others to challenge the legitimacy of all such establishments.