WEBVTT 00:11.740 --> 00:16.540 The next thing is that we're going to talk about the little bit of the limitations in natural languages, 00:16.540 --> 00:26.050 and this was something that Bertrand Russell was thinking a lot about in the early last century and 00:26.380 --> 00:33.010 yet again in such in many cases, the examples that are used are really kind of a little bit funny and 00:33.010 --> 00:33.420 corny. 00:34.250 --> 00:39.190 So they talked a lot about the king of France and whether he was born or not. 00:39.970 --> 00:43.610 So the king of France is bald, is famous quote, used here. 00:45.280 --> 00:46.420 What is that about then? 00:46.690 --> 00:52.260 It is about the natural languages could sometimes be very ambiguous. 00:54.940 --> 00:56.740 So if we think about this sentence. 00:56.740 --> 00:59.530 So the present king of France is bald. 01:01.240 --> 01:01.660 Right. 01:03.220 --> 01:05.260 And obviously it's false. 01:06.250 --> 01:10.390 But if it's false, hence its negation should be true. 01:11.410 --> 01:17.140 But the negation in natural language, like the present king of France is not bald is also false. 01:18.550 --> 01:21.080 So there's something fishy going on here. 01:21.520 --> 01:28.720 So what he thought is that if you're just using natural languages, you can fall into a lot of traps 01:28.720 --> 01:34.090 because you're not explicitly telling out the whole meaning. 01:35.920 --> 01:42.700 So what he coined here is something called definite descriptions and say that to be able to reason about 01:42.700 --> 01:45.430 this and see why the negation. 01:45.670 --> 01:47.320 So you cannot be both true and false. 01:47.330 --> 01:47.610 Right. 01:47.950 --> 01:51.930 So you can see why how this is negated in the correct way. 01:52.150 --> 01:56.570 You need to rewrite this sentence a little bit and write it logically like this. 01:56.570 --> 02:00.630 So if you know logic, you might be able to read the Bible, explain to you what it says. 02:00.640 --> 02:11.110 So there exists an ex such as that X is king of France and for all Y and if Y is also king of France, 02:11.110 --> 02:18.440 then Y equals X and X is more or a little bit more natural language here. 02:18.460 --> 02:22.840 So one, there is an X such that X is presently king of France. 02:23.170 --> 02:23.560 Right. 02:24.220 --> 02:33.610 For any X and Y, if X is presently king of France and Y is presently king of France, then X equals 02:33.610 --> 02:33.940 Y. 02:33.940 --> 02:39.040 So what he was saying here is that could only be one king of France at any given moment. 02:39.040 --> 02:44.200 There cannot be a way in which both are king of France and they're not the same object. 02:44.890 --> 02:48.760 And then three for every X that is presently King of France, X is ball. 02:49.150 --> 02:54.340 That is actually what we logically imply when we're seeing in natural language that the present king 02:54.340 --> 02:55.170 of France is born. 02:56.020 --> 03:02.050 But if we're divided in this way, we definitely directly see that why this is false. 03:02.050 --> 03:04.630 It's not false because the king of France is not bald. 03:04.810 --> 03:07.150 It's false because there is no king of France. 03:07.150 --> 03:09.830 So it's the first condition that fails and not the third one. 03:11.860 --> 03:14.710 So this is also a little bit important. 03:14.710 --> 03:20.230 And I think if you're a programmer, like I'm as I said, of hackers and I was a kid, you see that 03:20.230 --> 03:28.150 as a programmer, you need to think in this way all the time because unfortunately, computers is not 03:28.150 --> 03:29.710 that good at natural languages. 03:29.770 --> 03:32.440 They need to be told very binary what to do. 03:32.980 --> 03:39.760 And this is usually how you need to, for example, write in Eskil SQL Statement or something like that.