[MUSIC] So the epistemological question, that's what we're turning to now. When should you believe what another person tells you? Well, there are two views. And I'm going to pose them as two extreme views, to make it very clear what the disagreement is. Historically, they're associated with early modern philosophers from Scotland. So one answer is associated with the Aberdeen philosopher, Thomas Reid. And the other one is associated with Edinburgh philosopher, David Hume. Reid is on the side of it's being reasonable to just presume that other people are telling you the truth, that they're sincere, and that they're competent. You can just take it in. It's reasonable, just as it's reasonable to take perception at face value, to just assume that the world is exactly the way it looks to you. So too it's reasonable to believe what other people tell you. That's the extreme version. Whether Reid held it doesn't really matter, it's just an example of a famous philosopher who was inclined in that direction. On the other hand, there was David Hume. David Hume is reported to have held that there is no species of reason more common, more useful, and even necessary to human life, than the testimony of others. But even so he disagreed with Reid. He thought, or it's reported that he thought, that you should be skeptical. You should not simply presume that the other person is sincere, or competent, or knows what they're talking about. You need evidence in favor of their sincerity. You need evidence in favor of their competence. And it's gotta be evidence that you personally have acquired firsthand, of the reliability and sincerity of this person that you're talking to, that you're believing. Or the reliability of kinds of people, or kinds of reporters on kinds of subject matters. Or even the reliability of testimony of communication in general. So Hume we thought you need firsthand experience. Your observation of the way people work, their reports about the world that you have verified firsthand. You've figured out, aha, he told me you get Haggis on a Tuesday at that restaurant. I went there and I checked on a Tuesday, and he was right, so he's a sincere, reliable reporter, at least about Haggis. Now, I need to find out about other things. I need to do more verification of his reports, before I really have evidence that he's to be trusted. And by acquiring all this first-hand evidence, one person after another, I get to position where I've got justification for believing what other people tell me. So one extreme view associated with Reid is it's okay, it's safe, just take it in. The other extreme view is don't take it in at all. Don't believe any of it, until you're in a position to independently verify, by firsthand experiences stored in memory, that people's reports correlate with reality. That people acting, or talking, or communicating in a particular way, are sincere, and they're competent on certain kinds of subject matters. So either default trust or default disbelieve, until you've got evidence to overturn the suspension of judgment. So now we have an opposition. We have the view attributed to Reid, or the Reidian view, that you can just believe anybody. But that's crazy, because as adults, we shouldn't just believe what anyone tells us. And then we've got the radical Humean view, or the view attributed to Hume, that we should never believe anyone, until we figure out firsthand that they are worthy of our trust. That view can't be right either. One view is too permissive and the other view is too demanding. Of course, when you're at the situation like this, you know the truth must be somewhere in between. So I'm going to start arguing for a kind of compromise. And the first part of the compromise is to say what's true in both views. What's true in the Humean view is that there are plenty of times, when we should not simply believe what another person tells us. Because we know an awful lot about the way the world works. We know that there are times where people are out to mislead us. We know there are times where they cannot possibly be correct, where they themselves don't have the evidence. And something they just tell us, something that conflicts with something we already believe, we have a case of disagreement. These are all cases where we should stop and think again, before we believe what the other person tells us. But there is something right in Reid's position too. Notice the small child in believing what their parent tells them, is acquiring information about the world. And the parent is caring for the child. And it's not just a family unit that's at issue, but larger units of other caregivers of schools, of societies, of whole institutions, that run by the sharing of information one person to another. We are a deeply social species, where we depend upon each other's goodwill, each other's cooperation, for our long term existence. So if we're deeply social, doesn't it make sense that we can acquire information from one another? And if at times we're at odds with one another, which humans certainly are, doesn't it make sense to sometimes stop and be skeptical? So there's something very true in Reid's idea, that it's okay to take information in from one another, because of the kinds of creatures that we are, social creatures. And there is also something very true in Hume's idea that we shouldn't always just believe what another person tells us. Because we're not simply social, but we've got our own interests, and we're also very fallible, we end up making mistakes about a number of things. So we need to understand how these two pieces of the puzzle fit together, to explain why believing what another person tells you is a reasonable thing to do. And so a source of knowledge about the world.