I believe that the ocean is deep. I’m quite confident about it, in fact, but if someone ever asked me, “What are your sources for believing that the the ocean is deep?”, I would probably stutter for a few seconds and fail to come up with any kind of respectable answer. My belief is built on about a million pieces of evidence, but I can’t think of any particularly authoritative source that proves my case. I’ve seen some movies about submarines. Are movies a good source? No? Well, I’m pretty sure I’ve seen some documentaries about deep sea exploration, too. Which documentaries? Sorry, I don’t remember.
There’s a saying that two rationalists who share the same knowledge shouldn’t disagree. But of course, shared knowledge is impossible. You and I can read the same article about how much we should trust free markets to solve a problem, and we can come away with wildly different opinions about it. We might continue to disagree about it no matter how much time we spend discussing it, because the debate is not constrained to the article. It’s built on a lifetime’s worth of accumulated knowledge, models, and intuitions, as I wrote in the previous post. We can try to find other sources to bring into the discussion and back up our points, but we’ll never really be able to reveal all of our evidence, because so much of it is inaccessible to either of us. I know the ocean is deep, but I can’t give you a nice tidy list of 20 academic sources that will prove it to you. The same is true of everything I know.
In a typical conversation, I’m often afraid to voice my opinion on a lot of topics, because I’m afraid that I won’t be able to find the words to express what I mean. But even if I could find the worlds, complex beliefs are just too vague and complex a thing to express. It’s kind of a tragedy for our species. I wish there was a way for humans to do some kind of a mind-merge transmission of an entire worldview, but alas, we cannot. We can only ever give a shadow of our thoughts to someone else. Communication is hard.