I think Eliezer's point is less strong than you think: for one thing, reading a history book is a sensory experience, and fewer history books would proclaim that The Crusades occurred in worlds where they had not than in worlds where they had.

I think many of us have actually encountered liars on the Internet. I'm not sure what you mean when you say "lacking any factual evidence".

What about knowledge for the sake of knowledge? For instance I don't anticipate that my belief that The Crusades took place will ever directly affect my sensory experiences in any way. Does that then mean that this belief is completely worthless and on the same level as the belief in ghosts, psychics, phlogiston, etc.?

Wouldn't taking your chain of reasoning to its logical conclusion require one to "evict" all beliefs in everything that one has not, and does not anticipate to, personally see, hear, smell, taste, or touch? After all, how much personal sensory experience do you have that confirms the existence of atoms, for example?

DP

That makes sense if you're only evaluating complete strangers. In other words, your uncertainty about the population-inferred trustworthiness of a person is pretty high and so instead the mere (Occam Factor style) complexity of their statement is the overruling component of your decision.

In the stated case, this isn't a totally random stranger. I feel quite justified in having a less-than uninformative prior about trusting IRC ghosts. In this case, my rationally acquired prejudice overrules in inference about the truth of even somewhat ordinary tales.

("read something somewhere" does not qualify)

Wait, why not?

You're talking to a complete stranger on the internet. He doesn't know you, and cannot have any possible interest in deceiving you.

There's plenty of evidence that some people (a smallish minority, I think) will deceive strangers for the fun of it.

That's certainly sensible, and in But There's Still a Chance Eleiezer makes examples where this seems strong. In the above example, it depends a whole lot on how much belief you have in people (or, rather, lines of IRC chat).

I think then that your strength as a rationalist comes in balancing that uncertainty against some your prior trust in people. At which point, instead of predicting the negative, I'd seek more information.

I don't see that you did anything at all irrational. You're talking to a complete stranger on the internet. He doesn't know you, and cannot have any possible interest in deceiving you. He tells you a fairly detailed story and asks for you advice. For him to make the whole thing up just for kicks is an example of highly irrational and fairly unlikely behavior.

Conversely, a person's panicking over chest pains and calling the ambulance is a comparatively frequent occurrence. Your having read somewhere something about ambulance policies does not amount to having concrete, irrefutable knowledge that an ambulance crew cannot make an on-site determination that there's no need to take a person to the hospital. To a person without extensive medical knowledge there is nothing particularly unlikely about the story you were told.

Therefore, the situation is this -- you are told by a complete stranger that has no reason to lie to you a perfectly believable story. You have no concrete reason ("read something somewhere" does not qualify) to doubt either the story or the man's sanity. Thus there is nothing illogical about taking the story at face value. You did the perfectly rational thing.

Since there was no irrationality in your initial behavior, the conclusions that you arrive at further in your post are unfounded.

DP