Justified belief and conditional evidence

Plausibly, a belief that p is justified only if one has good evidence that p. But what about a case where instead of having evidence for a belief, one has evidence that if one believes it, then it's be true? (I'll call this the Belief Conditional.) For instance, tonight Sam will decide whether to watch Battlestar Galactica or Deep Space Nine. But Sam hates being shown to be wrong. So if she now comes to believe that she will watch, say, DS9, then come evening she will watch, say, DS9 in order to make her earlier belief true. She knows all this. She also hates suspending judgment. So she makes herself believe that she will watch DS9. (She's not deciding what she is to watch. The decision will come tonight.) Once she realizes that she has succeeding in coming to the belief that she will watch DS9, she has evidence that she will watch DS9. But we may suppose that there is a short period of time during which Sam hasn't yet realized that she believes she will watch DS9. During that short period of time, she doesn't have evidence that she will watch it. Instead, she just knows the conditional that if she believes she will watch it, she will watch it. I am inclined to think that Sam's belief that she will watch DS9 is reasonable and justified.

But I am not happy to extend this to a general claim that having justification for a Belief Conditional suffices for justification of unconditional belief. Here's a case that worries me. Suppose that having read a lot of papers defending an error theory about folk psychology, and generally hanging about in unfortunate philosophical company, Fred is in possession of strong evidence that nobody believes anything. But despite the evidence, ingrained habits make Fred continue to believe that someone believes something. (I take it for granted that the error theory is mistaken.) Of course, Fred does know the obvious necessary truth that if he believes that someone believes something, then someone believes something. But nonetheless given the evidence against folk psychology, I am inclined to think that Fred isn't justified in believing that somebody believes something.

I don't know how to distinguish the cases of Sam and Fred. I feel pulled to assimilate one to the other, but I don't know which I should assimilate to which.

The improbable and the impossible

This discussion from Douglas Adams' The Long Dark Tea-Time of the Soul (pp. 165-166) struck me as quite interesting:

[Kate:] "What was the Sherlock Holmes principle? 'Once you have discounted the impossible, then whatever remains, however improbable, must be the truth.'"

"I reject that entirely," said Dirk sharply. "The impossible often has a kind of integrity to it which the merely impossible lacks. How often have you been presented with an apparently rational explanation of something that works in all respects other than one, which is just that it is hopelessly improbable? Your instinct is to say, 'Yes, but he or she simply wouldn't do that.'"

"Well, it happened to me today, in fact," replies Kate.

"Ah, yes," said Dirk, slapping the table and making the glasses jump, "your girl in the wheelchair [the girl was constantly mumbling exact stock prices, with a 24-hour delay]--a perfect example. The idea that she is somehow receiving yesterday's stock market prices out of thin air is merely impossible, and therefore must be the case, because the idea that she is maintaining an immensely complex and laborious hoax of no benefit to herself is hopelessly improbable. The first idea merely supposes that there is something we don't know about, and God knows there are enough of those. The second, however, runs contrary to something fundamental and human which we do know about. ..."

This reminds me very much of the Professor's speech in The Lion, the Witch and the Wardrobe:

Either your sister is telling lies, or she is mad, or she is telling the truth. You know she doesn't tell lies and it is obvious that she is not mad. For the moment and unless any further evidence turns up, we must assume that she is telling the truth.

Both Dirk Gently and the Professor think that we need to have significantly greater confidence in what we know about other people's character than in our scientific knowledge of how the non-human world works. This seems to me to be just right. Our scientific knowledge of the world almost entirely depends on trusting others.

So, both C. S. Lewis and Douglas Adams are defending faith in Christ, though of course Adams presumably unintentionally. :-)

Folk psychology and scientific practice

All contemporary science evidentially depends on folk psychology. For instance:

• it is assumed that other scientists tend to say what they observed, and "observation" is a term of folk psychology; the evidence that they tend to say what they observed is based on evaluation of their motives;
• it is essential to the modern scientific enterprise that one be able to assume that technicians are doing what they claim, rather than producing equipment that displays fraudulent results; but the evidence that they are doing this is based on theories about the technicians' motives;
• the concept of reporting depends on folk psychological concepts; if nobody has intentions, nobody reports any results; but the reports of others are central to contemporary scientific practice.

Thus, those who are scientifically motivated to attack folk psychology are cutting the branch on which they sit.