Is It Irrational to Believe Without Evidence?

A conflict between faith and reason arises only when people use incorrect definitions of these terms. It is true that reason involves the use of the mind to make sense of the world and justify the beliefs we think are true, whereas faith is belief in things unseen. As St. Paul wrote, “We walk by faith, not by sight” (2 Cor. 5:6).  

However, faith is not “believing without evidence” or “belief in the absence of evidence” or “believing despite evidence.” Rather, it is defined as “evidence of things not seen” (Heb. 11:1, NABRE). St. Thomas explains this unusual use of the word evidence in the following way: 

Evidence induces the intellect to adhere to a truth, wherefore the firm adhesion of the intellect to the non-apparent truth of faith is called evidence here.  

In this way faith is distinguished from all other things pertaining to the intellect. For when we describe it as evidence, we distinguish it from opinion, suspicion, and doubt, which do not make the intellect adhere to anything firmly; when we go on to say, of things that appear not, we distinguish it from science and understanding, the object of which is something apparent.ii 

Faith gives us “evidence” of what is not immediately apparent to our limited intellect, on the ground that it is evident to the one who reveals it to us.iii The Catechism defines faith in this way: 

Faith is the theological virtue by which we believe in God and believe all that he has said and revealed to us” (1814).  

What moves us to believe is not the fact that revealed truths appear as true and intelligible in the light of our natural reason: we believe “because of the authority of God himself who reveals them, who can neither deceive nor be deceived” (156). 

This doesn’t mean that theists have no rational ground to stand on. Reason alone is enough to show us God exists, without supernatural faith. Even the Bible reminds us that we can discern God’s existence from the natural world, without any supernatural revelation: “For from the greatness and beauty of created things comes a corresponding perception of their creator” (Wis. 13:4-5). St. Paul himself wrote that God’s nature “has been clearly perceived in the things that have been made” (Rom. 1:19-20). Thus, the Catechism summarizes:  

The world, and man, attest that they contain within themselves neither their first principle nor their final end, but rather that they participate in Being itself, which alone is without origin or end. Thus, in different ways, man can come to know that there exists a reality which is the First Cause and final end of all things, a reality “that everyone calls God” (34). 

So, although it is true that not everything that is an object of faith can be proved by the light of natural reason (that is why it is faith!), faith is not thereby unreasonable or irrational. It is not unreasonable or irrational to rely upon the informed opinion of a trustworthy and competent source, when our own knowledge does not suffice on any given matter. We do this daily in our human lives. Why should it be irrational to do so when it comes to matters of faith? It would be irrational only if we placed our confidence in any and every opinion, without any effort to verify that source’s credibility. 

For example, by reason you know that a plane is capable of flying, but you have “faith”—i.e., belief that cannot be proven directly—that any particular plane is able to fly. You trust—but you don’t absolutely know—that the plane is maintained properly and the pilot is actually a pilot. Now, with some diligence you could corroborate these beliefs, but there are other beliefs that we must simply accept with faith-like trust. These include the belief that the laws of physics will not change suddenly mid-flight, causing the plane to crash. Such a belief cannot be proven but must simply be assumed.  

So when St. Paul writes that “we walk by faith, not by sight,” he doesn’t mean that we should blindly accept anything as true. He also doesn’t mean that we can’t have a natural, rational knowledge of God, or that this knowledge can’t inform and ground the beliefs that we hold by faith. (The Catholic Church even teaches as dogma that God can be known with certainty of human reason.) What Paul means, rather, is that in this life we are called to walk in confident expectation of what God has promised us and that we are not to become discouraged by trials. 

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