Have I Misunderstood?
Before considering whether what St. Thomas says about moral knowledge is true, let’s make sure I haven’t misunderstood him. Someone might suggest that when he says that the general principles of the natural law are the same “for all” as to knowledge – meaning that everyone knows them -- he really means that almost everyone knows them. As C.S. Lewis suggested, those thinkers who said that everyone knew the natural law “did not mean, of course, that you might not find an odd individual here and there who did not know it, just as you find a few people who are color-blind or have no ear for a tune. But taking the race as a whole, they thought that the human idea of decent behavior was obvious to everyone.”
No doubt some natural law thinkers did think this way about the race as a whole. But St. Thomas didn’t. In the following passage he clearly distinguishes between principles that are the same for all in every case, and principles that are the same for all with rare exceptions:
Consequently we must say that the natural law, as to general principles, is the same for all, both as to rectitude and as to knowledge. But as to certain matters of detail, which are conclusions, as it were, of those general principles, it is the same for all in the majority of cases, both as to rectitude and as to knowledge; and yet in some few cases it may fail, both as to rectitude, by reason of certain obstacles (just as natures subject to generation and corruption fail in some few cases on account of some obstacle), and as to knowledge, since in some the reason is perverted by passion, or evil habit, or an evil disposition of nature.
So although St. Thomas agreed that you might find an odd individual here and there who does not know one of the detailed precepts of the natural law, he really did believe that everyone knows the general principles of the natural law.
Someone might also propose that when St. Thomas says the general principles of the natural law are the same for all as to knowledge, he is speaking only of the first, indemonstrable principle of practical reason. In its ontological form, this may be expressed “good is that which all things seek after.” In its preceptive form, it may be expressed “good is to be done and pursued, and evil is to be avoided.” So the only thing that is the same for all as to knowledge – the only thing that each of us really knows – is that he ought, in fact, to pursue those things which are such as to draw his pursuit, and avoid those things which are such as to repel it. The knowledge of what these things are is not the same for all as to knowledge, so I am entirely mistaken in thinking that it includes such details as “Honor thy father and thy mother,” “Thou shalt not kill,” and “Thou shalt not steal.”
The difficulty with this interpretation is that St. Thomas explicitly contradicts it.
Hold that thought until Part 3.
1. C.S. Lewis, Mere Christianity, rev. ed. (New York: HarperCollins, 1952, 1982), p. 5.
2. Summa Theologiae I-II, Q. 94, Art. 4. I have omitted the final clause from this quotation, but only in order to return to it later.