Thomas Aquinas is widely regarded as the father of natural law theory due to his influential writings on the subject, particularly in his work 'Summa Theologica'.

Natural law theory holds that there are certain universal moral principles that are discoverable through human reason and that these principles should form the basis of law.

Natural law theory posits that the purpose of law is multifaceted, encompassing the protection of individual rights, the maintenance of social order, and the promotion of justice and fairness.

The right to life is often considered the most fundamental natural right, as it is a prerequisite for the enjoyment of all other rights.

John Locke is widely recognized for his articulation of the social contract theory of natural rights in his work 'Two Treatises of Government'.

The social contract theory posits that individuals enter into an implicit or explicit agreement with each other to form a society and government, thereby surrendering some of their natural rights in exchange for the benefits of living in a structured and orderly community.

Natural rights theory asserts that government power is constrained by the inherent and inalienable rights of individuals, which cannot be legitimately violated or overridden by the state.

Immanuel Kant maintained that natural rights are grounded in human nature and are universal and inalienable.

Natural law theory typically holds that natural law is superior to positive law (i.e., human-made law), and that positive law should conform to the principles of natural law.

The right to life is often closely linked to the right to self-defense, as individuals have a natural right to protect their own lives from harm.

One common criticism of natural law theory is that its principles are often vague and open to interpretation, leading to disagreements about their specific content and application.

Thomas Hobbes argued that individuals can alienate their natural rights to a sovereign in exchange for protection and security.

Natural law theory often posits a close relationship between natural law and morality, with natural law principles being derived from or closely aligned with moral principles.

The right to liberty often encompasses the right to freedom of expression, as individuals have a natural right to express their thoughts and ideas without fear of censorship or persecution.

Natural rights theory typically argues that natural rights are inherent and inalienable, and that they are grounded in human reason and morality.