1 00:00:02,980 --> 00:00:08,353 Another very common kind of inductive argument is an argument from analogy. 2 00:00:08,353 --> 00:00:13,512 We'll see that these arguments from analogy are very closely related to 3 00:00:13,512 --> 00:00:18,456 inferences to the best explanation. But first, we got to ask, what's an 4 00:00:18,456 --> 00:00:22,953 analogy? Analogy is basically a comparison between 5 00:00:22,953 --> 00:00:27,811 two things. It points out similarities between those 6 00:00:27,811 --> 00:00:32,295 two things. And analogies are given all the time. 7 00:00:32,295 --> 00:00:37,940 For example, a poet might say, her eyes were like emeralds. 8 00:00:37,940 --> 00:00:40,892 Well, in what way were they like emeralds? 9 00:00:40,892 --> 00:00:46,653 They might have had the same color, they might have shimmered like emeralds, they 10 00:00:46,653 --> 00:00:51,981 might have been valuable like emeralds. And the analogy, her eyes were like 11 00:00:51,981 --> 00:00:57,310 emeralds, doesn't really tell you exactly which respect her eyes resembled 12 00:00:57,310 --> 00:01:00,046 emeralds, but that's part of the point. 13 00:01:00,046 --> 00:01:05,375 When you're writing poetry, you want to stimulate creative comparisons and 14 00:01:05,375 --> 00:01:12,082 analogies of, so that readers of the poem can think about it in their own way and 15 00:01:12,082 --> 00:01:16,310 the same thing holds for other analogies in other areas. 16 00:01:16,310 --> 00:01:22,352 But because it's not very specific, some people think that analogies are just no 17 00:01:22,352 --> 00:01:28,016 good at all in arguments. Actually though, we use analogies and 18 00:01:28,016 --> 00:01:33,600 arguments all the time. Here's an example from public policy. 19 00:01:33,600 --> 00:01:38,713 They built a transportation system in the city of Houston, Texas. 20 00:01:38,713 --> 00:01:43,666 it worked pretty well. And then, the planners in the city of 21 00:01:43,666 --> 00:01:50,217 Phoenix, Arizona were wondering what kind of public transportation system to build 22 00:01:50,217 --> 00:01:56,129 there and they reasoned like this. They said, Phoenix is a lot like Houston 23 00:01:56,129 --> 00:02:00,283 in many ways, large population, hot during the summer, 24 00:02:00,283 --> 00:02:06,960 many, many people and large area. So, they said, Phoenix resembles Houston 25 00:02:06,960 --> 00:02:13,530 in a lot of ways. This type of transportation system worked in Houston, 26 00:02:13,530 --> 00:02:17,660 so it'll probably work well in Phoenix also. 27 00:02:17,660 --> 00:02:22,061 Now, what about law? Lot's of legal decisions are based on 28 00:02:22,061 --> 00:02:27,234 analogies too, because common law systems at least follow precedent. 29 00:02:27,234 --> 00:02:33,333 When judges decide a case one way in one time, at one point, then later on other 30 00:02:33,333 --> 00:02:36,808 judges are suppose to make similar decisions. 31 00:02:36,808 --> 00:02:42,753 So you can say for example, the Supreme Court declared that segregated public 32 00:02:42,753 --> 00:02:47,400 high schools are unconstitutional in the United States. 33 00:02:47,400 --> 00:02:53,254 Colleges are a lot like high schools, so, segregated public colleges are also 34 00:02:53,254 --> 00:02:58,877 unconstitutional in the United States. And then, med schools are a lot like 35 00:02:58,877 --> 00:03:02,728 colleges, so, segregated public medical schools are 36 00:03:02,728 --> 00:03:06,040 also unconstitutional in the United States. 37 00:03:06,040 --> 00:03:11,740 An that's the way the legal system evolves by drawing analogies among the 38 00:03:11,740 --> 00:03:15,900 different cases that come up within that jurisdiction. 39 00:03:15,900 --> 00:03:20,798 This form of argument in law might seem to be a real problem, because you don't 40 00:03:20,798 --> 00:03:25,510 say exactly what the similarities are. But actually, it's very useful, because 41 00:03:25,510 --> 00:03:29,788 it is predictable if you know that segregated high schools have been 42 00:03:29,788 --> 00:03:34,066 declared unconstitutional, you pretty know, much know that judges are going to 43 00:03:34,066 --> 00:03:37,600 find colleges unconstitutional too if they're segregated. 44 00:03:37,600 --> 00:03:42,517 and it also gives flexibility, so that judges can see when they're going 45 00:03:42,517 --> 00:03:47,369 too far, they say, well, that precedent is different and they distinguish the 46 00:03:47,369 --> 00:03:50,254 precedents. So by resting legal reasoning on 47 00:03:50,254 --> 00:03:55,303 arguments from analogy, they gain both predictability and also flexibility in 48 00:03:55,303 --> 00:03:59,041 the legal system. So arguments from analogy can be pretty 49 00:03:59,041 --> 00:03:59,907 useful. Fine, 50 00:03:59,907 --> 00:04:04,228 but policies and laws are all about norms and values. 51 00:04:04,228 --> 00:04:09,934 What about science and hard facts? Well, sciences use analogies, too. 52 00:04:09,934 --> 00:04:16,292 For example, scientists at one point didn't know what was at the center of the 53 00:04:16,292 --> 00:04:19,879 earth, but they found a bunch of meteors and 54 00:04:19,879 --> 00:04:25,722 meteorites that had a high iron content, much higher than the content of iron in 55 00:04:25,722 --> 00:04:29,790 the crust of the earth. So, they reasoned the earth must be like 56 00:04:29,790 --> 00:04:34,698 these other meteors and meteorites, so it must have a similar amount of iron 57 00:04:34,698 --> 00:04:39,864 in it, because they were produced in the same way in the history of the universe. 58 00:04:39,864 --> 00:04:44,190 But that means there must be a similar amount of iron in the Earth. 59 00:04:44,190 --> 00:04:46,967 If it's not in the crust, where could it be? 60 00:04:46,967 --> 00:04:50,389 It must be down in the core. So they figured, probably, 61 00:04:50,389 --> 00:04:53,680 the core of the earth has a lot of iron in it. 62 00:04:53,680 --> 00:04:59,143 That's just one example, but scientists actually use analogies a lot, and if you 63 00:04:59,143 --> 00:05:03,708 don't believe me, go read some psychological studies of scientific 64 00:05:03,708 --> 00:05:07,176 reasoning. But we're going to focus on an example 65 00:05:07,176 --> 00:05:10,986 from art history. Just imagine that you're going through 66 00:05:10,986 --> 00:05:16,224 the attic and you find an old painting. It looks a lot like a painting by the 67 00:05:16,224 --> 00:05:20,782 famous impressionist Cezanne, and if it is by Cezanne, it's worth an 68 00:05:20,782 --> 00:05:24,115 awful lot. But you got to figure out whether this 69 00:05:24,115 --> 00:05:28,750 painting is by Cezanne. How do you figure it out, because Cezanne 70 00:05:28,750 --> 00:05:32,060 didn't sign it? He didn't sign a lot of his paintings. 71 00:05:32,060 --> 00:05:35,294 Well, what you do is you look at other Cezanne 72 00:05:35,294 --> 00:05:39,429 paintings and try to figure out whether they're similar. And if you're not an 73 00:05:39,429 --> 00:05:43,511 expert, probably better check with an expert and have them do it, but they're 74 00:05:43,511 --> 00:05:46,895 going to do the same thing. They're going to compare this painting to 75 00:05:46,895 --> 00:05:51,191 a lot of other paintings that we know are by Cezanne, and then you can reason like 76 00:05:51,191 --> 00:05:54,897 this, this painting has a certain kind of 77 00:05:54,897 --> 00:06:01,294 brushwork and coloring and so on, and so on, subject matter, whatever. 78 00:06:01,294 --> 00:06:08,742 other paintings by Cezanne have very similar brushwork and color patterns and 79 00:06:08,742 --> 00:06:12,744 topic, and so on. Those other paintings are definitely by 80 00:06:12,744 --> 00:06:18,760 Cezanne, we know that, therefore this painting is probably by Cezanne as well. 81 00:06:18,760 --> 00:06:23,476 Now, that's an argument from analogy. This argument from analogy shares a 82 00:06:23,476 --> 00:06:28,455 certain form with the other arguments from analogy that we discussed before. 83 00:06:28,455 --> 00:06:33,040 And we can pick out that form by substituting letters for the English 84 00:06:33,040 --> 00:06:37,692 words in the English argument. For example, we can substitute the letter 85 00:06:37,692 --> 00:06:41,098 a for the subject, that is the topic of the argument, 86 00:06:41,098 --> 00:06:45,460 the painting that we don't know whether it's a Cezanne or not. 87 00:06:45,460 --> 00:06:52,051 And we can substitute the letters B, C, and D for the similar objects that are 88 00:06:52,051 --> 00:06:57,273 also Cezanne paintings. And we can substitute the letters P, Q, 89 00:06:57,273 --> 00:07:04,207 and R for the similarities between the paintings that we know are by Cezanne and 90 00:07:04,207 --> 00:07:10,285 the one that we're not sure of. And then we can substitute the letter X 91 00:07:10,285 --> 00:07:14,960 for that particular property of being by Cezanne. 92 00:07:14,960 --> 00:07:22,611 And when you substitute all those letters for the English words, then the argument 93 00:07:22,611 --> 00:07:29,890 simply says that object A has properties P, Q, and R and objects B, C, and D also 94 00:07:29,890 --> 00:07:36,515 have those properties P, Q, and R and B, C, and D also have the property X. 95 00:07:36,515 --> 00:07:41,834 So the subject, object A, probably also has the property X, 96 00:07:41,834 --> 00:07:46,220 namely, this painting is by Cezanne. Probably. 97 00:07:46,220 --> 00:07:51,349 Of course, since this argument only tries to show that the conclusion is probably 98 00:07:51,349 --> 00:07:55,718 true, it's an inductive argument. It's not valid, it's possible for the 99 00:07:55,718 --> 00:08:00,277 premises to be true and the conclusion false, namely, this painting might 100 00:08:00,277 --> 00:08:04,900 resemble all those other paintings in those respects and yet it's not by 101 00:08:04,900 --> 00:08:08,940 Cezanne. Secondly, the argument is defeasable. 102 00:08:08,940 --> 00:08:13,787 You can get some additional information that makes it really look like a bad 103 00:08:13,787 --> 00:08:16,871 argument. For example, you could turn the painting 104 00:08:16,871 --> 00:08:21,340 over and on the back you find the signature of a different artist like 105 00:08:21,340 --> 00:08:25,380 Sirah and then you realize this isn't by Cezanne at all. 106 00:08:25,380 --> 00:08:28,620 But nonetheless, the argument can be strong. 107 00:08:28,620 --> 00:08:34,197 It can always be stronger, because there can be more similarities and more 108 00:08:34,197 --> 00:08:38,794 important similarities. But, it can be a strong argument and a 109 00:08:38,794 --> 00:08:44,747 good argument, because it's inducted, so it doesn't event try or pretend to be 110 00:08:44,747 --> 00:08:47,620 valid. How can we tell when an argument for 111 00:08:47,620 --> 00:08:52,199 analogy really does give us a strong reason to believe the conclusion? 112 00:08:52,199 --> 00:08:56,974 What are the standards by which we measure how strong the argument is and 113 00:08:56,974 --> 00:09:01,030 how strong the reasons are? Well, one of them should be obvious. 114 00:09:01,030 --> 00:09:05,871 You know, of course, the premises have to be true and justified like in any 115 00:09:05,871 --> 00:09:09,964 argument. A standard that's relevant here is that 116 00:09:09,964 --> 00:09:15,111 when there are more important analogies, then it provides a stronger reason, 117 00:09:15,111 --> 00:09:18,679 because some analogies are just totally unimportant. 118 00:09:18,679 --> 00:09:22,865 The painting is square, other paintings by Cezanne are square, 119 00:09:22,865 --> 00:09:26,845 therefore, this is by Cezanne. Well, that's ridiculous, right? 120 00:09:26,845 --> 00:09:29,933 Because lots of painters use square canvases. 121 00:09:29,933 --> 00:09:34,805 For something that's important, that's going to be specific to Cezanne and very, 122 00:09:34,805 --> 00:09:40,020 very idiosyncratic is going to be more important for this type of argument. 123 00:09:40,020 --> 00:09:44,506 Secondly, when there are more analogies, because we don't know exactly which one 124 00:09:44,506 --> 00:09:48,394 is the one that's important. That's the point of an argument from 125 00:09:48,394 --> 00:09:51,086 analogy. You draw the analogy without knowing 126 00:09:51,086 --> 00:09:55,931 exactly which respect is the crucial one, so the more analogies that you have, the 127 00:09:55,931 --> 00:09:59,580 more likely you're going to hit on the ones that are crucial. 128 00:09:59,580 --> 00:10:07,517 So, if it's not just brushwork, it's also the type of paint that was used. 129 00:10:07,517 --> 00:10:12,214 It's also the color scheme that was used. It's also the geometric shapes. 130 00:10:12,214 --> 00:10:16,714 It's also the subject matter. It's a particular mountain that's close 131 00:10:16,714 --> 00:10:21,868 by where Cezanne lived and he painted a lot of that mountain, and on, and on, and 132 00:10:21,868 --> 00:10:24,673 on. The more analogies, the more likely that 133 00:10:24,673 --> 00:10:27,673 some of them are going to be the crucial ones. 134 00:10:27,673 --> 00:10:32,892 And therefore, the stronger the argument is and the stronger reason it gives you 135 00:10:32,892 --> 00:10:37,140 to believe that this particular painting is by Cezanne. 136 00:10:37,140 --> 00:10:41,683 But of course, there are always going to be some disanalogies as well, because 137 00:10:41,683 --> 00:10:46,459 Cezanne didn't paint the same thing over and over again exactly the way he did the 138 00:10:46,459 --> 00:10:50,743 first time. The fewer disanalogies, the stronger the 139 00:10:50,743 --> 00:10:53,513 argument. There'll always be some, or there 140 00:10:53,513 --> 00:10:58,140 wouldn't be much of an argument, they'd be exactly the same thing. 141 00:10:58,140 --> 00:11:04,365 But the fewer disanalogies and the less important those disanalogies are, then 142 00:11:04,365 --> 00:11:12,142 the stronger the argument is going to be. Next, the objects that you're comparing, 143 00:11:12,142 --> 00:11:17,648 because they're similar in various respects, that is, the other paintings 144 00:11:17,648 --> 00:11:22,465 that we know are by Cezanne. If they're quite diverse, then, that 145 00:11:22,465 --> 00:11:28,277 means that you have similarities among a diverse group that all share these 146 00:11:28,277 --> 00:11:32,742 particular properties. And that means that Cezanne continued to 147 00:11:32,742 --> 00:11:37,561 use those features throughout all the different types of paintings that he did 148 00:11:37,561 --> 00:11:42,719 and that means that it's going to be a stronger reason to believe that this 149 00:11:42,719 --> 00:11:50,690 painting is by Cezanne. Finally, the conclusion is weaker. 150 00:11:50,690 --> 00:11:54,965 You could say, therefore, this painting is definitely by Cezanne, 151 00:11:54,965 --> 00:11:59,037 it couldn't be anybody else. Well, that's kind of crazy, right? 152 00:11:59,037 --> 00:12:04,534 But if you say, it's probably by Cezanne, it has some chance it's by Cezanne, maybe 153 00:12:04,534 --> 00:12:09,216 you want to check it further. Then, you're weakening the conclusion and 154 00:12:09,216 --> 00:12:14,238 that can make the argument stronger. So in all of these different ways, we can 155 00:12:14,238 --> 00:12:19,081 assess how strong the argument from analogy is by looking at the respects in 156 00:12:19,081 --> 00:12:23,673 which the objects are analogous, the diversity among the objects that are 157 00:12:23,673 --> 00:12:27,510 analogous, the strength of the conclusion, and so on and so on. 158 00:12:27,510 --> 00:12:31,960 And that's how we assess an argument from analogy for strength. 159 00:12:31,960 --> 00:12:37,329 I want to close with one more example that raises interesting questions about 160 00:12:37,329 --> 00:12:42,627 the relationship between arguments from analogy and inferences to the best 161 00:12:42,627 --> 00:12:46,442 explanation. It concerns the pressing issue of whether 162 00:12:46,442 --> 00:12:50,958 Neanderthals were cannibals. Now it's not a pressing issue for most 163 00:12:50,958 --> 00:12:55,709 people, but it is a very pressing issue for people who study Neanderthals. 164 00:12:55,709 --> 00:13:00,916 And so it's quite a breakthrough when they found some bones in a cave that they 165 00:13:00,916 --> 00:13:05,798 knew was inhabited by Neanderthals. In that cave, next to what looked like a 166 00:13:05,798 --> 00:13:10,874 fire pit, there were bones of deer with markings of a certain sort that looked 167 00:13:10,874 --> 00:13:14,064 like they had been cutting the meat off the bone. 168 00:13:14,064 --> 00:13:19,075 And they also found bones of humans in that cave where they had been cutting, 169 00:13:19,075 --> 00:13:22,200 where they had similar markings. And they argued, 170 00:13:22,200 --> 00:13:26,733 since the bones have similar markings and these bones, 171 00:13:26,733 --> 00:13:31,006 the bones of the deer, were probably cut up for food. 172 00:13:31,006 --> 00:13:35,467 Well, the human bones where probably also cut up for food. 173 00:13:35,467 --> 00:13:41,102 So, they reached the conclusion that at least, sometimes, Neanderthals ate 174 00:13:41,102 --> 00:13:44,859 humans. What's interesting is that there are two 175 00:13:44,859 --> 00:13:49,987 ways to reconstruct this argument. First, you can reconstruct it as an 176 00:13:49,987 --> 00:13:54,216 argument from analogy. The bones of the humans were found in 177 00:13:54,216 --> 00:13:57,247 this location with these kinds of markings. 178 00:13:57,247 --> 00:14:02,887 The bones of deer were also found in this location with these kinds of markings, 179 00:14:02,887 --> 00:14:08,103 but the deer were cut up for food, therefore, the humans were probably also 180 00:14:08,103 --> 00:14:11,909 cut up for food. Now, that sounds like an argument from 181 00:14:11,909 --> 00:14:18,934 analogy when you think about it that way. But you can also reconstruct the argument 182 00:14:18,934 --> 00:14:24,598 as an inference to the best explanation. The bones of the humans had these 183 00:14:24,598 --> 00:14:28,675 markings on them and we're in this location, 184 00:14:28,675 --> 00:14:34,261 how do you explain that? The best explanation of why they have 185 00:14:34,261 --> 00:14:39,748 these particular kinds of markings is that they were cut up for food, 186 00:14:39,748 --> 00:14:44,440 therefore, the humans were probably cut up for food as well. 187 00:14:45,740 --> 00:14:52,728 Now notice, that both reconstructions of the argument make the argument look okay. 188 00:14:52,728 --> 00:14:59,371 And so, it's not clear, which tells you the real structure of the argument that 189 00:14:59,371 --> 00:15:04,560 the author was trying to give. And that means that arguments from 190 00:15:04,560 --> 00:15:09,359 analogy and inferences to the best explanation are actually very closely 191 00:15:09,359 --> 00:15:12,448 related, and sometimes, you can take an argument 192 00:15:12,448 --> 00:15:16,984 and reconstruct it either way. It's not going to affect very much how 193 00:15:16,984 --> 00:15:22,240 strong the argument is, but it might affect how you see the argument working. 194 00:15:22,240 --> 00:15:28,380 And the big difference is that, when you do an argument from analogy. 195 00:15:28,380 --> 00:15:32,077 You don't have to specify exactly which respect is important, 196 00:15:32,077 --> 00:15:36,866 so you can put out lots of analogies and hope that you hit the one that really 197 00:15:36,866 --> 00:15:39,897 matters. Whereas when you're doing an inference to 198 00:15:39,897 --> 00:15:43,821 the best explanation, then you have to pick out the specific 199 00:15:43,821 --> 00:15:48,987 property that gives you the explanation of the phenomenon that you observed. 200 00:15:48,987 --> 00:15:54,493 So it forces you to get a little bit more specific than with an argument from 201 00:15:54,493 --> 00:15:57,619 analogy. But otherwise, these two arguments are 202 00:15:57,619 --> 00:16:03,428 clearly very closely related and they're basically two different ways to argue for 203 00:16:03,428 --> 00:16:08,454 similar conclusions. For example, in this case, with the 204 00:16:08,454 --> 00:16:12,985 argument from analogy, you don't know whether it's the location next to the 205 00:16:12,985 --> 00:16:17,456 fire or the types of markings or maybe there are several different types of 206 00:16:17,456 --> 00:16:22,109 markings and they're all the same, but you don't know which ones are the ones 207 00:16:22,109 --> 00:16:27,184 that indicate how it was killed and which markings indicate how it was cut up to be 208 00:16:27,184 --> 00:16:29,661 eaten. And an argument from analogy can leave 209 00:16:29,661 --> 00:16:34,072 all that vague and just think that probably one of those similarities 210 00:16:34,072 --> 00:16:38,000 justifies the conclusion that the humans were cut up to be eaten. 211 00:16:38,000 --> 00:16:42,496 But if you're going to give an inference to the best explanation, then you're 212 00:16:42,496 --> 00:16:46,992 saying that these markings, for example, diagonal markings on leg bones, might 213 00:16:46,992 --> 00:16:51,305 suggest that they cut that up in a certain way, because that's how they 214 00:16:51,305 --> 00:16:55,801 prepared the deer meat and they were used to preparing deer meat that way. 215 00:16:55,801 --> 00:17:00,662 So they used similar cutting techniques when they were preparing human meat and 216 00:17:00,662 --> 00:17:05,401 you've got an explanatory story that's much more specific than a mere analogy, 217 00:17:05,401 --> 00:17:09,776 but it also commits you to a lot. So it might be questionable in various 218 00:17:09,776 --> 00:17:12,535 ways. So when you look at an argument like 219 00:17:12,535 --> 00:17:16,205 this, you've gotta decide which way to reconstruct the argument. 220 00:17:16,205 --> 00:17:20,574 It's an argument from analogy, or it's an inference to the best explanation. 221 00:17:20,574 --> 00:17:25,176 And the general rule is one that we saw long ago, in early weeks of this course, 222 00:17:25,176 --> 00:17:29,196 if you really want to understand an argument, you want to understand your 223 00:17:29,196 --> 00:17:33,565 opponents or you want to have a better argument for yourself, then you try to 224 00:17:33,565 --> 00:17:36,070 make the argument look as good as possible. 225 00:17:36,070 --> 00:17:40,854 So when you face a particular example like the Neanderthal example, you have to 226 00:17:40,854 --> 00:17:45,578 decide is this argument be, going to be better if I reconstruct it as an argument 227 00:17:45,578 --> 00:17:50,241 from analogy or is it going to be better if I reconstruct it as an inference to 228 00:17:50,241 --> 00:17:53,754 the best explanation? And the best reconstruction is going to 229 00:17:53,754 --> 00:17:56,480 be the one that makes the argument look best.