Suppose that someone accepts that life is meaningful for the reasons given in the last post.

Suppose he then says, “Since there’s no point in considering the possibility that life is meaningless, I might as well consider the fact that life is meaningful to be absolutely certain.”

Suppose he then forgets how he came to this point, and only notices that there is something he is absolutely certain about. He therefore says that this claim has a probability of 100%. And in order to be consistent, he adds that he is absolutely certain about having his absolute certainty.

He may well then proceed to develop a philosophy of human nature based on the position that he has the ability to possess absolute subjective certainty. And he may assign an extremely high probability to this philosophy, or even say that it is itself completely certain.

There is something very odd about this whole procedure. The starting point, that life is meaningful, is true. But the endpoint, a philosophy built on the possibility of absolute subjective certainty, is likely false, for reasons given previously. Where did we go astray? The problem appears in the second step above, when we go from excluding the possibility that life is meaningless, to saying that “life is meaningful” is absolutely certain.

It was pointed out in the last post that truth is only one of the possible motives for believing something, and there are other possible motives as well. This implies that “reasons for believing” something can be said to two ways. In one way, it signifies reasons why the thing would be true, or would be likely to be true. In another way, it signifies reasons why it would be good for someone to believe it. The fact that something is true is also a reason why it would be beneficial to believe it, and this could lead us to confuse the two meanings. Likewise, believing something involves claiming that it is true, and for this reason we might suppose that any reasons that make it good to believe something, should mean it’s likely to be true.

But in reality these kinds of reasons can be completely distinct. Thus it may be beneficial for a Muslim in an Islamic country to maintain his faith, in order to avoid being killed as an apostate. But this motive does not increase the probability of Islam in any way; it is not a reason which makes the thing true or likely to be true. The problem with the reasoning process described at the beginning of this post is that we collapsed these two types of reason: we had a moral reason to adopt the view that life is meaningful without reservation, but that moral reason does not increase the probability that life is meaningful. That life is meaningful should be considered to be extremely probable in itself, since it is simply common sense. But when we exclude potential reservations for moral reasons, we should not then suppose that we are suddenly absolutely certain.

St. Thomas gives another example of a moral reason for holding a certain opinion:

From the very fact that a man thinks ill of another without sufficient cause, he injures and despises him. Now no man ought to despise or in any way injure another man without urgent cause: and, consequently, unless we have evident indications of a person’s wickedness, we ought to deem him good, by interpreting for the best whatever is doubtful about him.

He admits that following this process may lead one into error, but says that the error is relatively minor compared to the danger of doing harm by thinking badly of a good man:

He who interprets doubtful matters for the best, may happen to be deceived more often than not; yet it is better to err frequently through thinking well of a wicked man, than to err less frequently through having an evil opinion of a good man, because in the latter case an injury is inflicted, but not in the former.

Again, as in the other cases, our moral reason is a real reason for thinking something, but it does not suddenly make that thing more probable than it otherwise was. And if we understand this in the latter way, we may fall into serious errors indeed. For example, a juror might think it is extremely certain that an alleged criminal is guilty. But then he might say to himself, “It would be more charitable to suppose that there is only a 90% chance he is guilty,” followed by, “It would be still more charitable to suppose that there is only an 80% chance he is guilty,” and so on, with the conclusion that the man is certainly innocent.

This is related to St. Thomas’s claim that when we judge well of another in this way, even when we are mistaken, this does not pertain “to the evil of the intellect, even as neither does it pertain to the intellect’s perfection to know the truth of contingent singulars in themselves.” This may be true insofar as it goes, meaning that the error in question is not a serious evil. But if we understand this to mean that our interpretation changes the probability of certain facts, this may indeed lead to serious evils, in a practical sense as in the case of the juror, or even in a speculative sense as in our original example. Since a moral reason does not in fact make the thing more probable, someone who asserts that the thing is more probable is asserting something false, even if the thing in question happens to be true in fact, and if he attempts to justify this false assertion of greater probability, he will be able to do so only by continuing to assert other falsehoods. And thus one begins to weave a tangled web indeed.

None of this implies that one should not believe things for moral reasons. It simply means that one should make sure to distinguish between the reasons that make something probably true, and reasons that make it good to think it is true, and not to confuse the two by supposing that one’s moral reasons make something likely to be true.