St. Thomas was a naturalist; he believed that law mirrored a natural law world order made known to humans by their own process of reasoning & by the divine revelation of Christian prophets.
He was strongly influenced by Plato & especially Aristotle, Aquinas firmly believed in the necessary connection between law and reason; reason invested law with its legitimacy. He proposed practical reason tells one what ought to be done & avoid evil.
Being able to view and study multiple philosophers at his time, he has developed & understood the distinctions between eternal law, natural law and human law. * Eternal law is the government of the universe according to the divine will of God; * Natural law is the “imprinting” of eternal law on humans.
He says natural laws that were first set should not be taken away, although they can be altered.
St. Thomas Aquinas reinforces the belief of natural law theorists that the validity of a law is dependent upon its moral content or