The vehicle by which man knows Natural Law is reason and understanding. Here, Aquinas makes a second important distinction – some men will understand more, some less. Aquinas is not promoting an egalitarian view of reason. All men may know, but all men will not know equally.
The following list is taken from the Summa Theologica Prima Secundae question 93, entitled, The Eternal Law. A proper understanding of the Eternal Law of God, the Divine Government, serves as an excellent foundation to issues such as politics, natural law, divine providence, hell, and nature.
Opus Dei Father C.J. McCloskey, a Church historian and research fellow at the Faith and Reason Institute in Washington, referred to Robert Spencer as "perhaps the foremost Catholic expert on Islam in our country."