The question of which (if any) rights are natural and which are merely legal is an important one in philosophy and politics. Critics of the concept of natural rights argue that the only rights that exist are legal rights, while proponents of the concept of natural rights say that documents such as the United States Declaration of Independence and the Universal Declaration of Human Rights demonstrate the usefulness of recognizing natural rights. The focus of natural rights in the United States Declaration of Independence is expressed in the legal philosophy known as Declarationism.
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. Conversely, the concept of natural rights is used by some anarchists to challenge the legitimacy of all such political establishments.
The idea of human rights is also closely related to that of natural rights; some recognize no difference between the two and regard both as labels for the same thing, while others choose to keep the terms separate to eliminate association with some features traditionally associated with natural rights. Natural rights, in particular, are considered beyond the authority of any government or international body to dismiss. The Universal Declaration of Human Rights is an important legal instrument enshrining one conception of natural rights into international soft law.
The idea that animals have natural rights is one that has gained the interest of philosophers and legal scholars in the 20th century, and as such, even on a natural rights conception of human rights, the two terms may not be synonymous.While the existence of legal rights has always been uncontroversial, the idea that certain rights are natural or inalienable also has a long history dating back at least to the Stoics of Late Antiquity, and descending through the Protestant Reformation and the Age of Enlightenment to today.
The Stoics held that no one was a slave by their nature; slavery was an external condition juxtaposed to the internal freedom of the soul (sui juris). Seneca the Younger wrote: � It is a mistake to imagine that slavery pervades a man's whole being; the better part of him is exempt from it: the body indeed is subjected and in the power of a master, but the mind is independent, and indeed is so free and wild, that it cannot be restrained even by this prison of the body, wherein it is confined. �
Likewise, the notion of inalienable rights was found in early Islamic law and jurisprudence, which denied a ruler "the right to take away from his subjects certain rights which inhere in his or her person as a human being." Islamic rulers could not take away certain rights from their subjects on the basis that "they become rights by reason of the fact that they are given to a subject by a law and from a source which no ruler can question or alter." These ideas may have later influenced John Locke's concept of inalienable rights through his attendance of lectures given by Edward Pococke, a professor of Arabic studies.