This document provides an overview of natural law theory, including its origins in ancient Greek philosophy and its development through thinkers like Aquinas, Grotius, and Locke. It discusses two main types of natural law theory: a theory of morality that argues moral propositions can be objectively true or false and are derived from human nature; and a theory of law that argues there is an overlap between law and morality such that legal validity depends at least partly on moral content. The document then examines conceptual naturalism as a form of natural law theory of law, outlining classical naturalism's view that human laws are only valid if consistent with natural law, deriving authority from it. It notes criticisms of conceptual naturalism but argues these