A popular citation of Martin Luther King, Jr.’s justly-famous “Letter from Birmingham Jail” is his reference to natural law and Thomas Aquinas:
How does one determine whether a law is just or unjust? A just law is a man-made code that squares with the moral law or the law of God. An unjust law is a code that is out of harmony with the moral law. To put it in the terms of St. Thomas Aquinas: An unjust law is a human law that is not rooted in eternal law and natural law. Any law that uplifts human personality is just. Any law that degrades human personality is unjust.
The Witherspoon Institute has announced today its project, “Natural Law, Natural Rights, and American Constitutionalism,” which “will serve as an online resource center for students, teachers, and educated citizens to learn about the intellectual traditions of natural law and natural rights, particularly within American political and constitutional history.”