1 00:00:02,920 --> 00:00:07,800 We've learned that inferences to the best explanation, are inductive arguments. 2 00:00:07,800 --> 00:00:11,157 They're not valid. And they are defeasible. 3 00:00:11,157 --> 00:00:15,154 But still, they might be strong and good arguments. 4 00:00:15,154 --> 00:00:20,111 They might give you good reasons to believe their conclusions. 5 00:00:20,111 --> 00:00:25,307 Great, they might be, sure. But, how do you tell whether they really 6 00:00:25,307 --> 00:00:31,862 are strong arguments and good arguments? We need standards for determining when an 7 00:00:31,862 --> 00:00:36,580 inference to the best explanation is a good argument. 8 00:00:36,580 --> 00:00:43,016 And to understand those standards, we're going to view another skit made by my 9 00:00:43,016 --> 00:00:51,706 students a few years ago. It's time for class. 10 00:00:51,706 --> 00:00:57,395 It's obviously the cult of the Magic Dragon here. 11 00:00:57,395 --> 00:01:01,306 Right. Do you know all those songs are about 12 00:01:01,306 --> 00:01:05,751 drugs? Was Peter and Paul manning drugs? 13 00:01:05,751 --> 00:01:09,217 Yeah, I know. Whoa, where is everybody? 14 00:01:09,217 --> 00:01:12,151 Beats me. It's Monday, isn't it? 15 00:01:12,151 --> 00:01:16,684 Yeah, first day of the week. Remember the weekend? 16 00:01:16,684 --> 00:01:18,017 Hm. The weekend? 17 00:01:18,017 --> 00:01:20,862 . Yeah, I remember, vaguely. 18 00:01:20,862 --> 00:01:23,935 Good times. Now, it's back to work. 19 00:01:23,935 --> 00:01:26,555 It's Monday. But, what time is it? 20 00:01:26,555 --> 00:01:30,597 It's 11:15.15. Well, isn't that when class is supposed 21 00:01:30,597 --> 00:01:32,094 to start? . 22 00:01:32,094 --> 00:01:38,008 Here's the start of a good explanation. There are surprising circumstances that 23 00:01:38,008 --> 00:01:41,624 need to be explained. Yeah, maybe my watch is fast. 24 00:01:41,624 --> 00:01:44,149 It has been giving me some trouble lately. 25 00:01:44,149 --> 00:01:46,915 Do you check yours? I don't wear a watch. 26 00:01:46,915 --> 00:01:49,741 I just ask you when I need to know the time. 27 00:01:49,741 --> 00:01:52,387 Great! So, I'm your designated time keeper. 28 00:01:52,387 --> 00:01:54,852 kind of, but there's usually a clock around. 29 00:01:54,852 --> 00:01:57,799 One right there. Okay, so we know its 11:1515. 30 00:01:57,799 --> 00:02:00,387 Right. In any entrance for the best explanation, 31 00:02:00,387 --> 00:02:04,050 it is crucial to get an accurate picture of what you're trying to explain. 32 00:02:04,050 --> 00:02:10,210 In this case, if it were 11:10 instead of 11:15, then the explanation may be 33 00:02:10,210 --> 00:02:14,176 different, or, there might be nothing at all to explain. 34 00:02:14,176 --> 00:02:17,845 So, where is everybody? Well, maybe everybody else is late. 35 00:02:17,845 --> 00:02:21,328 After all, the professor does show up a few minutes late. 36 00:02:21,328 --> 00:02:26,054 He told me that he doesn't like to start teaching right away, because he doesn't 37 00:02:26,054 --> 00:02:28,977 like when he's talking and students walk in. 38 00:02:28,977 --> 00:02:33,425 Oh, that makes me mad. So maybe, they're coming in later, 39 00:02:33,425 --> 00:02:38,352 because they don't want to wait around for him to start talking. 40 00:02:38,352 --> 00:02:43,114 It's one of those vicious circles. Okay, maybe that's it. 41 00:02:43,114 --> 00:02:46,891 But then some students should start showing up. 42 00:02:46,891 --> 00:02:49,683 So, let's just wait and see. 'Kay. 43 00:02:49,683 --> 00:02:52,801 . Enough is enough. 44 00:02:52,801 --> 00:02:56,582 If people are coming they'd be here by now. 45 00:02:56,582 --> 00:03:02,385 I mean, the professor's been late, but he's never been this late. 46 00:03:02,385 --> 00:03:09,067 Anne refutes Bob's explanation by pointing out new facts that falsify Bob's 47 00:03:09,067 --> 00:03:12,760 hypothesis that all the students are late. 48 00:03:12,760 --> 00:03:19,091 A good explanation has to be compatible with all the facts, not just the 49 00:03:19,091 --> 00:03:23,599 particular ones that it's trying to explain. 50 00:03:23,599 --> 00:03:29,504 Bob's hypothesis can't be the best explanation of why the students aren't 51 00:03:29,504 --> 00:03:33,573 there at 11:1515, if they're still not there by noon. 52 00:03:33,573 --> 00:03:37,643 . Well that brings us right back to where 53 00:03:37,643 --> 00:03:39,159 we started. . 54 00:03:39,159 --> 00:03:44,266 Why isn't anybody else here? Your guess is as good as mine. 55 00:03:44,266 --> 00:03:48,256 Well, well my guess is that everybody else is here. 56 00:03:48,256 --> 00:03:55,883 We just can't see or hear them. I bet they're laughing at us right now. 57 00:03:55,883 --> 00:04:01,837 [LAUGH]. I bet the professor's up there jabbering 58 00:04:01,837 --> 00:04:07,872 away right now, like he always does. [uuu]. 59 00:04:07,872 --> 00:04:10,821 Oh, I hope this material is not on the test. 60 00:04:10,821 --> 00:04:13,899 [LAUGH], Congratulation's, you've proved me wrong. 61 00:04:13,899 --> 00:04:17,561 Your guess is not as good as mine. Why? 62 00:04:17,561 --> 00:04:20,705 Humans can't become invisible. How do you know? 63 00:04:20,705 --> 00:04:22,398 Have you ever seen it? No. 64 00:04:22,398 --> 00:04:25,481 They're invisible, that's why I've never seen it. 65 00:04:25,481 --> 00:04:27,960 Okay. But the laws of physics don't allow 66 00:04:27,960 --> 00:04:32,978 humans to be come silent and invisible. Anne dismisses Bob's new hypothesis, 67 00:04:32,978 --> 00:04:37,271 because it's not conservative. It conflicts with well established prior 68 00:04:37,271 --> 00:04:41,348 beliefs in physics. If you start believing that humans can 69 00:04:41,348 --> 00:04:46,927 become invisible, you'll have to give up everything you know about how light and 70 00:04:46,927 --> 00:04:48,531 matter work. . 71 00:04:48,531 --> 00:04:53,482 Besides, if they were here, the seats wouldn't be popped up like this. 72 00:04:53,482 --> 00:04:56,341 Nope. Because, besides being invisible and 73 00:04:56,341 --> 00:04:59,270 silent, these students are also weightless. 74 00:05:01,160 --> 00:05:07,135 No smell either. Okay, so there is no way to tell whether 75 00:05:07,135 --> 00:05:10,529 or not they're students here. You're catching on. 76 00:05:10,529 --> 00:05:15,647 But the laws of physics still don't allow people to be weightless, invisible, and 77 00:05:15,647 --> 00:05:18,717 silent. Well, the laws of physics are based on 78 00:05:18,717 --> 00:05:22,172 observation. And there is no way these students can be 79 00:05:22,172 --> 00:05:25,434 observed at all. The laws of physics can't apply to 80 00:05:25,434 --> 00:05:28,889 something that can't be observed, or these students. 81 00:05:28,889 --> 00:05:33,815 So then nothing could possibly tell whether or not there's students in these 82 00:05:33,815 --> 00:05:35,158 chairs? Exactly. 83 00:05:35,158 --> 00:05:39,444 Hey, Ed, we're here live with an unidentifiable, unobservable student. 84 00:05:39,444 --> 00:05:44,430 What's it like to be unobservable? Okay, back to you Ed. 85 00:05:44,430 --> 00:05:48,584 Pretty sweet, huh? No, it is not sweet. The only reason why 86 00:05:48,584 --> 00:05:53,084 your idea isn't falsified, is because it's not falsifiable. 87 00:05:53,084 --> 00:05:58,325 If you can't prove it then it's useless. I mean, you might as well say there's 88 00:05:58,325 --> 00:06:01,525 invisible elephants floating around. . 89 00:06:01,525 --> 00:06:06,630 Ann rejects Bob's new explanation on the grounds that it's not falsifiable. 90 00:06:06,630 --> 00:06:10,510 It's compatible with anything that could possibly happen. 91 00:06:10,510 --> 00:06:15,888 But that means that it can't explain why one thing happens rather than another. 92 00:06:15,888 --> 00:06:18,134 It's completely empty. . 93 00:06:18,134 --> 00:06:22,146 I was just joking. This is a philosophy class after all. 94 00:06:22,146 --> 00:06:25,127 Okay, I don't mind jokes, but, let's get serious, 95 00:06:25,127 --> 00:06:27,589 because it's doesn't help us with our problem. 96 00:06:27,589 --> 00:06:33,071 Why isn't anybody here? Speaking of joking, maybe they're all 97 00:06:33,071 --> 00:06:38,958 playing a trick on us, maybe they decided not to show up. 98 00:06:38,958 --> 00:06:43,548 [LAUGH]. Okay but why would they do that? 99 00:06:43,548 --> 00:06:47,933 Is it April Fool's Day? No, it's January. 100 00:06:47,933 --> 00:06:50,385 Oh. Well then I don't know why they're 101 00:06:50,385 --> 00:06:52,256 tricking us. They just are. 102 00:06:52,256 --> 00:06:57,354 Okay, I can't believe that unless you can tell me why they would be so silly. 103 00:06:57,354 --> 00:07:01,549 Anne is criticizing Bob's new explanation, because it is not deep. 104 00:07:01,549 --> 00:07:05,033 It's shallow, because it depends upon a principle that 105 00:07:05,033 --> 00:07:08,260 is not itself explained, and needs to be explained. 106 00:07:09,582 --> 00:07:15,003 I don't know. I, I guess the professor just decided to cancel class because he 107 00:07:15,003 --> 00:07:21,093 didn't feel like teaching today. Maybe, but then other students wouldn't 108 00:07:21,093 --> 00:07:26,291 know so they would be here. Unless, he emailed the entire class, then 109 00:07:26,291 --> 00:07:30,675 they would know. Did you check your email recently? 110 00:07:30,675 --> 00:07:34,983 About an hour ago. Then maybe he emailed us the past hour. 111 00:07:34,983 --> 00:07:38,743 I guess, I mean that would explain why nobody's here. 112 00:07:38,743 --> 00:07:43,019 Some professors do cancel class at the last minute, but not him. 113 00:07:43,019 --> 00:07:46,820 He's too strict. I've had five classes with him and he's 114 00:07:46,820 --> 00:07:52,114 never canceled class at the last minute. If you miss even one class in this 115 00:07:52,114 --> 00:07:56,254 course, you will fail. So, maybe this time it's different. 116 00:07:56,254 --> 00:08:00,462 Yeah, and maybe the sun didn't rise. Either way, it's totally out of 117 00:08:00,462 --> 00:08:03,448 character. Anne's point is that Bob's new 118 00:08:03,448 --> 00:08:07,792 explanation is Ad Hoc. It applies only to the very circumstances 119 00:08:07,792 --> 00:08:12,340 that it was invoked to explain, and it doesn't apply to other cases. 120 00:08:12,340 --> 00:08:15,273 That means that it lacks power and breadth. 121 00:08:15,273 --> 00:08:20,840 Okay. But, I've got it! 122 00:08:20,840 --> 00:08:25,625 Classes must have been cancelled for some reason. 123 00:08:25,625 --> 00:08:29,491 What reason? maybe it's a holiday. 124 00:08:29,491 --> 00:08:35,826 Okay, what holiday? Martin Luther King. 125 00:08:35,826 --> 00:08:41,113 That's it, it's Martin Luther King Day. That would explain it. 126 00:08:41,113 --> 00:08:45,730 I mean, nobody goes to class but a fool on a holiday. 127 00:08:45,730 --> 00:08:50,010 Hi, I'm here. I guess that makes us both fools. 128 00:08:50,010 --> 00:08:53,321 Yeah. So I guess that's why he didn't send the 129 00:08:53,321 --> 00:08:56,277 note cause he figured no one would come here. 130 00:08:56,277 --> 00:09:01,336 I bet he wrote it down in the syllabus. It also explains why no one is in the 131 00:09:01,336 --> 00:09:05,739 whole classroom building. Bob's new explanation works because it 132 00:09:05,739 --> 00:09:09,550 has all of the virtues that the other explanations lacked. 133 00:09:09,550 --> 00:09:13,952 It's powerful, broad, deep, simple, conservative and not falsified, and yet 134 00:09:13,952 --> 00:09:17,368 falsifiable. Those virtues make his explanation good 135 00:09:17,368 --> 00:09:20,593 or in his words, sweet. You're right. 136 00:09:20,593 --> 00:09:25,204 You know, I think there's some kind of ceremony today with the President of the 137 00:09:25,204 --> 00:09:29,464 college and some big hot shot from Washington for Martin Luther King Day. 138 00:09:29,464 --> 00:09:32,032 So probably that's where the whole class is. 139 00:09:32,032 --> 00:09:34,191 That's why they're not here. Maybe. 140 00:09:34,191 --> 00:09:38,802 But, even if there weren't a ceremony, the fact that it's Martin Luther King Day 141 00:09:38,802 --> 00:09:43,062 would explain why nobody's here. So you don't really need to add anything 142 00:09:43,062 --> 00:09:45,688 else. Ann rejects Bob's newest explanation 143 00:09:45,688 --> 00:09:49,365 because it's not modest. It commits him to more matters of fact 144 00:09:49,365 --> 00:09:52,400 than are needed to explain the observations at hand. 145 00:09:54,606 --> 00:10:00,249 So I guess the holiday explains it all. Well not really, we still don't know why 146 00:10:00,249 --> 00:10:03,414 that big head keeps popping in on the side. 147 00:10:03,414 --> 00:10:07,474 That's one I can't figure out myself. That's so weird. 148 00:10:07,474 --> 00:10:12,773 It kind of looks like this kid that used to babysit me when I was younger. 149 00:10:12,773 --> 00:10:18,140 This whole exchange can be seen as a single argument that takes the form of a 150 00:10:18,140 --> 00:10:23,302 long inference to the best explanation. The first premise is an observation, 151 00:10:23,302 --> 00:10:27,539 nobody else is in the room. A second premise is an explanation. 152 00:10:27,539 --> 00:10:32,774 The hypothesis that class was cancelled because of the holiday, plus accepted 153 00:10:32,774 --> 00:10:38,145 facts and principles, gives a suitably strong explanation of the observation in 154 00:10:38,145 --> 00:10:43,200 premise one, namely, the observation that nobody else is in the room. 155 00:10:43,200 --> 00:10:48,274 Premise three is a comparison. No other hypothesis provides an 156 00:10:48,274 --> 00:10:54,240 explanation nearly as good as the holiday hypothesis in premise two. 157 00:10:54,240 --> 00:10:59,464 And the conclusion, is that the holiday hypothesis in premise two is true. 158 00:10:59,464 --> 00:11:03,543 The most controversial premise is probably premise three. 159 00:11:03,543 --> 00:11:08,982 It says that no other explanation provides nearly as good an explanation as 160 00:11:08,982 --> 00:11:13,133 the holiday hypothesis. To justify this premise, we need to 161 00:11:13,133 --> 00:11:18,643 compare other possible explanations. And that's exactly what the two students 162 00:11:18,643 --> 00:11:23,220 do throughout the skip. Their discussion can then be summarized 163 00:11:23,220 --> 00:11:27,323 in this background argument that supports premise three. 164 00:11:27,323 --> 00:11:33,111 The hypothesis that the other students are late is falsified by the passing of 165 00:11:33,111 --> 00:11:36,335 time. The hypothesis that the other students 166 00:11:36,335 --> 00:11:41,683 are invisible is not conservative. The hypothesis that the other students 167 00:11:41,683 --> 00:11:47,178 are undetectable is not falsifiable. The hypothesis that the other students 168 00:11:47,178 --> 00:11:52,453 are playing a joke is not deep. The hypothesis that the professor skipped 169 00:11:52,453 --> 00:11:57,459 class is not powerful or broad. The hypothesis that the other students 170 00:11:57,459 --> 00:12:02,322 are at a ceremony is not modest. No other hypothesis seems plausible. 171 00:12:02,322 --> 00:12:08,329 Therefore no other hypothesis provides an explanation nearly as good as the holiday 172 00:12:08,329 --> 00:12:12,692 hypothesis in premise two. Even if the other explanations are 173 00:12:12,692 --> 00:12:17,984 inadequate, the inference of the best explanation fails unless the holiday 174 00:12:17,984 --> 00:12:22,990 hypothesis succeeds at explaining why there's nobody else in the room. 175 00:12:22,990 --> 00:12:27,617 Premise two claims that the holiday hypothesis does explain why there's 176 00:12:27,617 --> 00:12:32,231 nobody else in the room. So we need to analyze why it succeeds. 177 00:12:32,231 --> 00:12:36,308 And to do that we can look at another background argument. 178 00:12:36,308 --> 00:12:40,315 The holiday hypothesis explains why nobody else is there. 179 00:12:40,315 --> 00:12:46,150 Because if classes were cancelled because of the holiday, then nobody else would be 180 00:12:46,150 --> 00:12:49,454 there. That is, nobody else would be in the room 181 00:12:49,454 --> 00:12:53,795 at the usual time. The holiday hypothesis is also broad, 182 00:12:53,795 --> 00:12:59,045 because it explains other actual observations, such as the observation 183 00:12:59,045 --> 00:13:05,146 that the whole building is empty. The holiday hypothesis is also powerful, 184 00:13:05,146 --> 00:13:09,986 because it applies to many separate cases, for example it explains why 185 00:13:09,986 --> 00:13:13,740 students won't be there on future holidays. 186 00:13:13,740 --> 00:13:16,666 The holiday hypothesis is also falsifiable. 187 00:13:16,666 --> 00:13:21,839 Because two students might find out that classes were not cancelled for the 188 00:13:21,839 --> 00:13:25,106 holiday. The holiday hypothesis is not falsified 189 00:13:25,106 --> 00:13:30,687 because the two students do not actually find out that classes were not cancelled 190 00:13:30,687 --> 00:13:34,499 for the holiday. And similarly for other ways to falsify 191 00:13:34,499 --> 00:13:38,680 the hypothesis. The Holiday Hypothesis is also 192 00:13:38,680 --> 00:13:45,560 conservative because it does not conflict with any prior well established beliefs. 193 00:13:45,560 --> 00:13:51,393 The holiday hypothesis is also deep because it does not depend on any 194 00:13:51,393 --> 00:13:56,060 assumptions that need, that lack independent explanation. 195 00:13:56,060 --> 00:14:01,060 So the holiday hypothesis explains why nobody else is there. 196 00:14:01,060 --> 00:14:07,266 And it's broad, powerful, falsifiable but not falsified, conservative, deep. 197 00:14:07,266 --> 00:14:12,579 Therefore the holiday hypothesis, plus accepted facts and principles, gives a 198 00:14:12,579 --> 00:14:16,856 suitably strong explanation of why nobody else is in the room. 199 00:14:16,856 --> 00:14:22,169 These two background arguments use a common list of virtues that are usually 200 00:14:22,169 --> 00:14:26,791 called explanatory virtues. In general, one explanation is better or 201 00:14:26,791 --> 00:14:30,517 stronger than another if it has more of these virtues. 202 00:14:30,517 --> 00:14:35,829 When you understand these explanatory virtues, then you've mastered inference 203 00:14:35,829 --> 00:14:38,106 to the best explanation. Right? 204 00:14:38,106 --> 00:14:41,552 Right. Now we can go on and look at other kinds 205 00:14:41,552 --> 00:14:43,180 of inductive argument.