Believing on faith

Some students seem to believe that in the absence of conclusive proof any view is as good as any other and that one’s position on most everything must be based on faith. So, they say: “It’s true that I believe in my god’s existence or in my god’s characteristics on faith, but everybody else does the same with respect to what they believe in; for example, a physicist believes in his own science just like I believe in my god.” In other words, they hold the view that

1. If X cannot be proved to be true with absolute certainty, any opinion about X’s truth is just as good as any other

Or that

2. If X cannot be proved to be true with absolute certainty, accepting X amounts to accepting X on faith.

Are (1) or (2) true or at least reasonable?

Different disciplines have different views as to when something is proved; however, the biggest philosophical distinction is between a priori and a posteriori proofs.

An a priori proof is one that does not rely on experiment at all. For example, mathematical proofs are a priori. Suppose that all observed triangles have been measured to have the sum of their internal angles equal to 180 degrees. Would that amount to proof, in geometry? Hardly. By contrast, Euclid’s argument does amount to a proof because it is formally correct (it contains no fallacy) and does not rely on experiment but on reasoning alone from the axioms of Euclidean geometry. (Check it out!). There is little debate about a priori proofs. For example, within Euclidian geometry the previous theorem is unchallenged; we are very certain that it is true because the only way for it to be false is if we have made a mistake in our reasoning, and when it comes to mathematical reasoning we can be sure that we have not made any mistake. In mathematics, we are as close to absolute certainty as we can get.

An a posteriori proof, by contrast, depends on experience: in your reasoning, at some point one must appeal to observation or experiment. For example, suppose you are marooned on an island, and see what seems to be a human footprint. You look at it carefully, compare it with your own footprint, and conclude that it is a human footprint and it isn’t yours. You reason that some other human has been, and perhaps still is, on the island. Note that in your reasoning you assume as true that your eyes do not deceive you, your feet did not change size or shape without you noticing, and rain or wind did not produce the imprint, just to mention a few. Each of these could be false, but the probability of that is very low and consequently you are justified in reaching your conclusion. Suppose now that you find more evidence for the presence of another human such as the remains of what seems to be a campfire. As the evidence mounts, at some point you will have proved your conclusion because it would be totally unreasonable of you to believe otherwise. Still, your proof is not as certain as one in mathematics: all that you observed could have been caused by the weather, animals, or what have you. However, you reason, the probability of that is so low that it can be dismissed. As long as you know that, your belief is not based on faith but on evidence. If someone told you that the presence of another human is uncertain because you never saw him and therefore “your belief is just theory and not fact” you would be hardly moved. The presence of another human is by far the best explanation of the evidence. Hence, you’ll start acting as if there was, and perhaps still is, another human on the island; nobody in her right mind would do otherwise.

Similarly, suppose you read in a biology journal that at about three weeks a human embryo has a two chamber heart and pharyngeal arches. Should you believe what the author says? Imagine that you find out that the biologist in question has a good reputation, that the journal is highly regarded, its selection criteria for publication strict, and that the result is in conformity with the theory of evolution. At this point you would be justified in believing what the author says. Is it possible that the author is wrong or cheating? Of course it is; in fact, it has happened. However, given the selection criteria of the journal and the author’s reputation, it’s more likely that the author is right and honest than wrong or dishonest. Suppose now that other researchers make the same observation and publish their results in reputable journals. Is it possible that there is a vast conspiracy by nefarious embryologists whose aim is to convince us that early human embryos have pharyngeal arches like fish embryos? Of course it is, but its likelihood is really small. So, it would be unreasonable for you not to believe what these scientists say. In both cases your conclusion would not based on faith but on evidence, strong in the first case and very strong in the second. Crucially, you could check for yourself and find out, like all who have done it, that your conclusion is actually true! At this point one who has never actually observed a three week old human embryo would conclude that it has been proved that at about three weeks old we have a two chamber heart and pharyngeal arches, and behave accordingly.

Suppose now that you take a class in biology and conclude that the Theory of Evolution is true. Well, it surely could be false. That many believe it is true is far from being conclusive evidence: after all, most humans who have ever existed have not believed that they lived on the third planet from a humdrum star. However, the probability that the Theory of Evolution is false is very small because of the vast amount of evidence, both direct and indirect, in favor of the theory. Now one might say that biologists have not observed the emergence of Synapsids (the line to which we belong) within Amniota, and therefore they must believe it on faith. But this would be wrong. When you were on the island, you did not observe another human, and yet your belief in the presence of another human was justified on evidence, not faith, and it was not “just theory” in any significant sense. (Note that “theory” is not synonymous with “guess.”)

But suppose that evidence is not as good as in the previous cases. Imagine that you are trying to determine whether to invest in stock A, B, or C. The available evidence is ambiguous because it points to different directions, and experts disagree on how to rank the stocks even as they agree that any of the three stocks could be the best. Contrary to the previous cases, nobody can prove anything. Here comes Green who says to invest in C because the last time he invested in a stock whose name began with C he made money, or because the number of occurrences of the letter C in his religious book is greater than that of the letter A or B, or because nobody can disprove that C is the best option, or because Zeus appeared to him in dream and told him to buy C. Would you believe that C is the best on the basis of Green’s evidence? You would be unwise if you did. Not all opinions are on the same level: one must look at the evidence. From the fact that evidence is partial it does not follow that anything goes. For example, to count for evidence something must be relevant to what is being discussed, and what Green put forth is not.

Suppose now that you rank A highest on the basis of partial evidence. Is your belief that A is the best based on faith? Hardly; you evaluated the evidence, found that for A the most convincing, concluded that A is probably the best, and so you chose A. Of course, you could be mistaken, and it would be wrong for you to claim that you know that A is the best, but from this it does not follow that your belief is based on faith.