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Can we be sure of anything?


"We cannot be sure of anything!" "Are you sure of that?" "Of course I'm sure!"

Charles E. Rice

This dialogue is not wholly imaginary. If you asked the average high school student, Catholic or otherwise, whether, apart from mere sense impressions, he could know anything with certainty, he would answer that he could not. Nor is this attitude confined to secondary schools. Colleges have an abundance of professors who are convinced that the mind cannot really know anything with certainty. In a case of which this writer knows, one professor announced on the first day of class that "The first thing to learn is that there are no absolutes." When a student asked, "Are you absolutely sure of that?", the professor's answer went unrecorded.

An interesting question is why people pay tuition to study under professors who say that they do not know, and cannot know, anything. We are not talking here about sense impressions. The normal reliability of sense impressions is self-evident. Only a fool would ask for "proof" that the truck he sees is really bearing down upon him. If he is sane, he will jump out of the way. If he does not trust the evidence of his senses, he will be dead. The issue with which we are concerned is not the reliability of sense impressions. It is whether we can know anything beyond those impressions. The answer is, yes.

The first thing that we know with absolute certainty is the principle of contradiction: A thing cannot be and not be at the same time under the same aspect. Or another way of saying it is that the same thing cannot be affirmed and denied at the same time. This pen I am holding in my hand is a pen. It cannot be at the same time a wheelbarrow. In terms of its pen-ness, that is, whether it is or is not a pen, it cannot be both a pen and not a pen. It is also black, hard, cylindrical, five inches long, etc. But these incidental qualities relate to different aspects. They do not concern the essential question: Is it a pen? We know with absolute certainty that, in terms of its penness, its character of being or not being a pen, it cannot be both a pen and not a pen. This is self-evident. It is either a pen or it is not a pen. It cannot be both. Anyone who thinks that this item, in terms of its pen-ness, is both a pen and not a pen, is unfit to carry on any rational discussion. And if he asks for proof, if he says, "Prove that this cannot be both a pen and a wheelbarrow," the answer is that there is no proof. As a self-evident proposition, the principle of contradiction is known beyond doubt to all rational beings.

The statement, "We cannot know anything," is itself absurd. For the person making that statement at least claims to know that he cannot know anything. And if he says, "I just am not sure I can be sure of anything," he acknowledges at least that he is sure he is not sure. Or if he says, "We cannot know anything that cannot be verified by sense impression or by experimentation," he is speaking absurdity because that statement itself cannot be verified by sense impression or by experimentation.

Any rational person will acknowledge the truth of the principle of contradiction. The self-evident truth of that principle provides the first example of what we can know with certainty. Beyond that, man is capable of knowing the essences or the natures of things. He can know that this is a pen and not a wheelbarrow. Man understands essences through the operation of his senses and his intellect. He perceives individual things through his senses and imagination and through his intellect he knows the essences of those things:

Each person has his own intellect which has two functions: it abstracts essences from sense-perceived individuals; this abstracted essence is then intelligible; it is impressed on the passive intellect. On reflection the passive intellect understands that one essence belongs to many individuals, forming a class which can again be further unified by still more abstract ideas into wider classes. Abstraction terminates in the idea of being which includes God, the only self-existent being. "I am who am." [Cornelius Hagerty, C.S.C., The Problem of Evil (1978), 18]

All we are concerned about in this chapter is to demonstrate that, a part from sense impressions, the mind can attain to knowledge that is certain. Throughout the rest of this course we will discuss what we can know and how we can know it.


Charles E. Rice. "Can we be sure of anything?" Chapter 2 in Truth in Christ: Notes on Teaching Some Elements of the Catholic Faith (Notre Dame, Indiana: Cashel Institute, 1983), 4-6.

This article reprinted with permission from the author Charles E. Rice.


Charles E. Rice is Professor Emeritus of Law at the University of Notre Dame Law School and Visiting Professor of Law at Ave Maria School of Law, Ann Arbor, Michigan. He has served as a consultant to the U.S. Commission on Civil Rights and to various Congressional committees on constitutional issues and is an editor of the American Journal of Jurisprudence. Professor Rice is also chairman of the Center for Law and Justice International in New Hope, Kentucky, and a director of the Thomas More Center for Law and Justice in Ann Arbor. He is faculty advisor and an assistant coach of the Notre Dame Boxing Club. He and his wife, Mary, have ten children and they reside in Mishawaka, Indiana. Professor Rice is the author of many books, including 50 Questions on the Natural Law: What It Is and Why We Need It and most recently The Winning Side: Questions on Living the Culture of Life.

Copyright 1983 Cashel Institute



Copyright 2004 Victor Claveau. All Rights Reserved