G. K. Chesterton, in his book Orthodoxy, discusses the meaning of being “entirely convinced” of something:

It is very hard for a man to defend anything of which he is entirely convinced. It is comparatively easy when he is only partially convinced. He is partially convinced because he has found this or that proof of the thing, and he can expound it. But a man is not really convinced of a philosophic theory when he finds that something proves it. He is only really convinced when he finds that everything proves it. And the more converging reasons he finds pointing to this conviction, the more bewildered he is if asked suddenly to sum them up. Thus, if one asked an ordinary intelligent man, on the spur of the moment, “Why do you prefer civilisation to savagery?” he would look wildly round at object after object, and would only be able to answer vaguely, “Why, there is that bookcase … and the coals in the coal-scuttle … and pianos … and policemen.” The whole case for civilisation is that the case for it is complex. It has done so many things. But that very multiplicity of proof which ought to make reply overwhelming makes reply impossible.

We could think about this in terms of probability. The person who is “entirely convinced” would be like the person who assigns a probability of 100%, while someone who is “partially convinced” might assign a somewhat lower probability.

As Chesterton says, the person who assigns the lower probability has no difficulty defending his position. He can point to various things which he has found, arguments and evidence, that support his position.

But what about the person who assigns the probability of 100%? According to Chesterton, he is in difficulty because he finds that everything supports his position. And indeed, this is reasonable. For if some things support your position and some things do not, how could you suppose that there is no chance that you are mistaken? On the other hand, if you think that literally everything supports your position, you might well suppose that you cannot be mistaken about it.

Of course, as we have said many times on this blog, it is unreasonable in fact to claim such certainty, and it is unreasonable in fact to claim that everything supports your position. So being “entirely convinced” in Chesterton’s sense here is a bad thing, not a good thing.

Chesterton goes on to apply this to his belief in Catholicism:

There is, therefore, about all complete conviction a kind of huge helplessness. The belief is so big that it takes a long time to get it into action. And this hesitation chiefly arises, oddly enough, from an indifference about where one should begin. All roads lead to Rome; which is one reason why many people never get there. In the case of this defence of the Christian conviction I confess that I would as soon begin the argument with one thing as another; I would begin it with a turnip or a taximeter cab.

This is not a good thing, for the above reasons. We could describe this situation in another way. We saw in the previous post that consistent testimony where there should be inconsistent testimony leads to a weakening of the evidence. If a dozen eyewitnesses agree in every respect, this is not good evidence for their claim, but good evidence that they are collaborating. In a similar way, if it seems to you that “everything proves it,” this is very good evidence that you are incapable of distinguishing between things that support your position and things that do not.

This also provides a fuller explanation for the fact that the person who is entirely convinced in Chesterton’s sense finds it difficult to argue for his position. Chesterton’s point that when there are too many possibilities, it is difficult to choose one of them, has some validity. But more fundamentally, the person who is entirely convinced in this way is not even engaging in reasonable argument in the first place; while the person who is partially convinced at least has the possibility of engaging in this kind of argument.