The relations among nature, reason, and revelation are mysterious for both Protestants and Catholics. Consider John Paul II’s remark that “the primary and definitive source for studying the intimate nature of the human being is the Most Holy Trinity.” Read carelessly, this might seem to imply the utter futility of philosophizing about the constitution of the human person; nothing would be left but ­theology.

Not so, for revelation shines at least five different kinds of light on nature. First is the light of precept : God commands or forbids something that the mind itself can recognize as right or wrong. Certain moral matters are so obvious that at some level everyone already knows them”the wrong of adultery, for example, and the wrong of theft.

Of course, this raises the question: If we already know them, then why is God’s precept necessary? In one sense, it is impossible to be mistaken about these fundamentals; they are right before the eye of the mind. And yet, as Thomas Aquinas remarks, “they need to be promulgated, because human judgment, in a few instances, happens to be led astray concerning them.” [For more click here.]