Late in Aquinas' career as a professor in Paris, a quodlibetal question was put to him: Should professors of theology settle these or any other disputed questions by reason or by authority? His response indicates why his work remains relevant to non-believers. Here it is in full:
Any activity is to be pursued in a way appropriate to its purpose. Disputations have one or other of two purposes.
One sort is designed {ordinatur} to remove doubts about whether such-and-such is so. In disputations of this sort you should above all use authorities acceptable to those with whom you are disputing; with Jews, for example, you should appeal to the authority of the Old Testament; with Manichees, who reject the Old Testament, you should use only the New; with Christians who have split off from us, e.g. the Greek [Orthodox], who accept both Testaments but reject the teaching of our [Catholic] saints, you should rely on the authority of the Old and New Testaments and of those church teachers {doctores} they do accept. And if you are disputing with people who accept no authority, you must resort to natural reasons.
Then there is the professorial academic disputation, designed not for removing error but for teaching, so that those listening may be led to an understanding of the truth with which the professor {magister} is concerned. And here you must rely upon reasons, reasons which track down the root of the truth and create a real knowledge of how it is that your assertions are true. Otherwise, if professors settle questions by bare authorities, listeners are indeed told that such-and-such is so, but gain nothing in the way of knowledge or understanding {scientiae vel intellectus}, and go away empty.
(John Finnis, Aquinas: Moral, Political, and Legal Theory [New York: Oxford University Press, 1998], 11-2 [brackets in original; footnotes and Finnis's italics omitted])
