Thomas Aquinas on the Limits of Human Knowledge

Posted 1/14/2019

Some Reading Notes

Perusing the beginning of St. Thomas’ Summa this morning, it struck me how honest Thomas is about the sources of his knowledge, and the nature of the conclusions reachable by human reason. Human knowledge is but a feeble endeavor, and depends finally on a faith as childlike as that of the mystics.

In the first article, Thomas addresses why we need theology at all. Man is directed to God, he says, but this direction is beyond the grasp of our reason. We all have an intuition that we are destined to something higher than we can perceive. “Hence it was necessary for the salvation of man that certain truths which exceed human reason should be made known to him by divine revelation.” There is a natural law, natural signs of the nature of God and our relationship to him, but far from being plain and founded upon solid logic, Thomas says that God gave us the scriptures “because the truth about God such as reason could discover, would only be known by a few, and that after a long time, and with the admixture of many errors.” This is not a statement made by a man particularly optimistic about the evangelistic possibilities of apologetics. In reply to the objection that God must be known through reason, in fact, Thomas replies that, “Although those things which are beyond man’s knowledge may not be sought for by man through his reason, nevertheless, once they are revealed by God, they must be accepted by faith.” In other words, not only is human reason so insufficient that God may not be sought for by man through only the aid of his reason, the foundation of the science which Thomas seeks to illuminate through the Summa is built finally on faith.

We are aware of the feebleness of our own knowledge; sacred science provides us with, not the firm result of our reason, but a source of salvation from our reason. Without sacred science we could never reach what Thomas calls “wisdom,” the higher knowledge which sets our reason in order, and only through which our reason can see anything. “This doctrine is wisdom above all human wisdom; not merely in any one order, but absolutely.” The very principles on which sacred science operates are above the understanding of our reason: “Sacred doctrine derives its principles not from any human knowledge, but from the divine knowledge, through which, as through the highest wisdom, all our knowledge is set in order.”

This is an example of a distinction that I have found valuable in discussions of apologetics. It is not the task of apologetics, at least insofar as they operate within the limits of human reason that we all, Christian and non-Christian alike, have at our disposal, to demonstrate the “truth” of Christianity, but only its reasonableness. Through apologetics we can show that our belief is not irrational, but not that it is rationally necessary. As Thomas points out later in this section on sacred doctrine, however, no science does this; no science can or tries to prove its first principles.

Thomas himself is one of the greatest of the Church’s doctors, firmly convinced of the truth of the sacred science’s conclusions about God and the world, and yet he is the first to admit, here at the beginning of the greatest of this theological works, that divine truth is virtually unknowable on our own. Only through faith in the person of God, and in his scriptures, can we attain to any real knowledge. But even this knowledge that we attain to through faith is often nowhere near as firm as we hope. The Christian life is full of doubt, fear, and uncertainty. Thomas is perfectly honest about this too. In Article 5 of “On Sacred Doctrine,” he discusses the nobility of theology over the other sciences. The first and principle objection to this noble status for theology is its uncertainty. It establishes so little certitude, the objection goes, that it not to be accorded much nobility.

To reply to this objection, Thomas establishes an important distinction: the certitude that a particular fact may have in itself, and the certitude that we as fallible humans may have in our knowledge of that certain fact. The claims of scripture are self-evident in themselves, in that they are true, but they are not self-evident to us. Even the existence of God itself, Thomas admits, is not self-evident to us fallible humans, although he believes that the existence of God can be demonstrated from effects. Of this sacred science, Thomas says that “this science surpasses other speculative sciences; in point of greater certitude, because other sciences derive their certitude from the natural light of human reason, which can err; whereas this derives its certitude from the light of divine knowledge, which cannot be misled: in point of the higher worth of its subject-matter because this science treats chiefly of those things which by their sublimity transcend human reason; while other sciences consider only those things which are within reason’s grasp.”

Despite the uncertainty inherent within religious belief, Thomas nevertheless finds it the most important pursuit we can have: “It may well happen that what is in itself the more certain may seem to us the less certain on account of the weakness of our intelligence, ‘which is dazzled by the clearest objects of nature; as the owl is dazzled by the light of the sun’ (Metaph. ii, lect. i). Hence the fact that some happen to doubt about articles of faith is not due to the uncertain nature of the truths, but to the weakness of human intelligence; yet the slenderest knowledge that may be obtained of the highest things is more desirable than the most certain knowledge obtained of lesser things.”

Thomas goes on from these statements to make some general notes about the methods of this science that is so far above human reason. Since the foundation of Christian belief is faith in a personal God and in his scriptures, it does not seek to prove this foundation, but goes on from this foundation to prove other things. In this way, it is similar to the other sciences: “As other sciences do not argue in proof of their principles, but argue from their principles to demonstrate other truths in these sciences: so this doctrine does not argue in proof of its principles, which are the articles of faith, but from them it goes on to prove something else.” To be clear, Thomas does not believe that human reason is useless—“sacred doctrine makes use even of human reason, not, indeed, to prove faith (for thereby the merit of faith would come to an end), but to make clear other things that are put forward in this doctrine”—but nevertheless believes it to be useless in establishing a foundation for belief.