WEBVTT 00:00:00.000 --> 00:00:05.840 (intro music) 00:00:05.840 --> 00:00:08.270 Hi! I'm Eugen Fischer, senior lecturer in 00:00:08.270 --> 00:00:10.410 philosophy at the University of East Anglia. 00:00:10.410 --> 00:00:13.170 Today, we will look at some paradoxes about perception, 00:00:13.170 --> 00:00:15.270 known as "arguments from illusion." 00:00:15.270 --> 00:00:19.850 These arguments ask us to consider cases of non-veridical perception, 00:00:19.850 --> 00:00:22.509 where something appears different than it is. 00:00:22.509 --> 00:00:28.330 For example, when we look at round coins sideways, they appear elliptical. 00:00:28.330 --> 00:00:31.720 Similarly, when seen from a greater distance, a man may 00:00:31.720 --> 00:00:35.500 seem less than half as tall as another man of roughly equal height. 00:00:35.500 --> 00:00:38.180 Or consider the phenomenon known as "refraction." 00:00:38.180 --> 00:00:40.160 When a straight straw is partially 00:00:40.160 --> 00:00:42.359 immersed in water, it looks bent. 00:00:42.359 --> 00:00:45.029 All of these facts are familiar from daily life. 00:00:45.029 --> 00:00:47.079 None of them is normally contested. 00:00:47.079 --> 00:00:50.510 But these familiar facts seem to have a striking consequence. 00:00:50.510 --> 00:00:53.120 They seem to imply that we are cut off from the 00:00:53.120 --> 00:00:57.030 physical objects around us by a veil of experience within us. 00:00:57.030 --> 00:01:01.240 The eighteenth-century philosopher David Hume drew this consequence very swiftly 00:01:01.240 --> 00:01:03.699 when reflecting on another relevant fact: 00:01:03.699 --> 00:01:07.189 as we all know, the table look smaller and smaller to people 00:01:07.189 --> 00:01:09.030 the further away the move from it. 00:01:09.030 --> 00:01:11.790 Hume observes that the table we see seems to 00:01:11.790 --> 00:01:16.500 get smaller as we move away from it, yet there is no change in the size of the 00:01:16.500 --> 00:01:20.760 real table, which is made of wood and stands in the parlor, regardless of 00:01:20.760 --> 00:01:22.480 whether we look at it or not. 00:01:22.480 --> 00:01:25.880 Hume immediately infers that we cannot be aware of this 00:01:25.880 --> 00:01:30.280 unchanging, real table, and therefore must be aware of something else. 00:01:30.280 --> 00:01:34.130 He concludes that thing we see is an image of the table, 00:01:34.130 --> 00:01:37.990 whose size does change as we move away from the table. 00:01:37.990 --> 00:01:41.090 This image then is present to us in our minds. 00:01:41.090 --> 00:01:43.629 In other words, when you look at the table, 00:01:43.639 --> 00:01:48.239 you are only aware of a mental image, not of the physical table. 00:01:48.239 --> 00:01:51.950 To unpack this rather swift but historically influential argument, 00:01:51.950 --> 00:01:53.790 let's have a closer look at the case of 00:01:53.790 --> 00:01:58.090 the round coin that appears elliptical to you when you look at it sideways. 00:01:58.090 --> 00:02:00.520 What exactly are you aware of in this case? 00:02:00.520 --> 00:02:02.100 Describe your experience, rather than the objects around you. 00:02:02.100 --> 00:02:05.450 Describe what you are aware of, 00:02:05.450 --> 00:02:09.610 without making any judgment about the physical object you're facing, without 00:02:09.610 --> 00:02:12.480 judging that object's shape, or size, 00:02:12.480 --> 00:02:14.830 or color, or any other property of it. 00:02:14.830 --> 00:02:17.009 That the right thing to say then, it seems, 00:02:17.009 --> 00:02:20.870 is that you're aware of an elliptical, golden patch. 00:02:20.870 --> 00:02:23.870 This judgment is often called the "phenomenal judgment." 00:02:23.870 --> 00:02:26.570 The first step the argument elicits such 00:02:26.570 --> 00:02:28.829 phenomenal judgments about cases of 00:02:28.829 --> 00:02:32.870 non-veridical perception, like that of the coin or Hume's table. 00:02:32.870 --> 00:02:37.149 The second step has us figure out what kind of thing we're then aware of. 00:02:37.149 --> 00:02:39.579 What could that elliptical patch be? 00:02:39.579 --> 00:02:43.669 It cannot be the coin, because the coin is round and not elliptical. 00:02:43.669 --> 00:02:47.339 So you're clearly aware of something other than the coin. 00:02:47.339 --> 00:02:50.189 Hume called this other thing an "image." 00:02:50.189 --> 00:02:54.569 A now more common, and more neutral term, is "sense-datum." 00:02:54.569 --> 00:02:56.969 Now continue to look in the direction of the coin. 00:02:56.969 --> 00:02:58.939 How many different things do you see? 00:02:58.939 --> 00:03:01.159 How many different things can you direct your 00:03:01.159 --> 00:03:03.690 attention at and say that you are aware of? 00:03:03.690 --> 00:03:07.560 Clearly, you cannot first direct your attention at something elliptical and 00:03:07.560 --> 00:03:09.960 then shift your attention elsewhere to 00:03:09.960 --> 00:03:13.560 become aware of something else that could be the coin. 00:03:13.560 --> 00:03:16.669 So you are aware only of one thing, not of two. 00:03:16.669 --> 00:03:20.439 We already concluded that you are aware the sense-datum. 00:03:20.439 --> 00:03:23.239 Therefore, you cannot be aware of the coin too. 00:03:23.259 --> 00:03:27.099 At any rate, not in the same way or sense. 00:03:27.099 --> 00:03:31.379 But of course you are aware of the coin in some sense. 00:03:31.379 --> 00:03:33.369 You know perfectly well that you are 00:03:33.369 --> 00:03:37.139 looking at a coin rather than, say, a marble or a dice. 00:03:37.139 --> 00:03:41.629 Proponents of the argument from illusion therefore commonly called the cautious 00:03:41.629 --> 00:03:45.560 conclusion that the subjective sense-datum is the only thing you are directly aware of 00:03:45.560 --> 00:03:48.200 when looking at the coin sideways. 00:03:48.200 --> 00:03:51.440 At the same time, you may be indirectly 00:03:51.440 --> 00:03:53.669 aware of the physical object, namely, 00:03:53.669 --> 00:03:57.649 in virtue of being directly aware of the sense-datum. 00:03:57.649 --> 00:04:00.949 So far, we have rehearsed the first half of the argument. 00:04:00.949 --> 00:04:05.480 The second half then generalizes from the particular case of non-veridical 00:04:05.480 --> 00:04:08.509 perception to all cases of perception. 00:04:08.509 --> 00:04:10.989 This generalizing step builds on the 00:04:10.989 --> 00:04:13.120 observation that sense data and physical 00:04:13.120 --> 00:04:17.270 objects are the most radically different kinds of things. 00:04:17.270 --> 00:04:21.390 For a start, the sense-datum is rather less stable than the coin. 00:04:21.390 --> 00:04:24.990 The color patch changes its shape the moment you move, 00:04:24.990 --> 00:04:27.050 while the coin retains its shape. 00:04:27.050 --> 00:04:32.700 The sense-datum also vanishes the moment you close your eyes, while the coin vanishes 00:04:32.700 --> 00:04:34.910 only the moment it gets melted down, 00:04:34.910 --> 00:04:38.120 or some other major physical mishap occurs to it. 00:04:38.120 --> 00:04:43.300 So the sense-datum and its properties depend upon you, the observer, 00:04:43.300 --> 00:04:48.590 in ways in which the physical object and its properties do not. 00:04:48.590 --> 00:04:51.480 Sense data are subjective, ever-changing, 00:04:51.480 --> 00:04:55.860 and fleeting, like the flickering of a candle or its dying smoke. 00:04:55.860 --> 00:04:57.980 Physical objects, by contrast, are 00:04:57.980 --> 00:05:01.900 objective and stable, like solid tables and hard coins. 00:05:01.900 --> 00:05:04.300 the intuitive key assumption now is 00:05:04.300 --> 00:05:07.980 that our awareness of such radically different things should 00:05:07.980 --> 00:05:11.140 constitute qualitatively different experiences. 00:05:11.140 --> 00:05:14.480 We should be able to tell from the subjective quality of our 00:05:14.480 --> 00:05:19.330 experience whether we are aware of a sense-datum or of a physical object. 00:05:19.330 --> 00:05:20.330 But compare. 00:05:20.330 --> 00:05:23.850 Have a look at this pencil, which is partially immersed in water. 00:05:23.850 --> 00:05:26.220 To most people, it seems bent. 00:05:26.220 --> 00:05:28.850 If you are like them, you are now directly 00:05:28.850 --> 00:05:33.060 aware of a sense-datum or color patch, which actually is bent. 00:05:33.060 --> 00:05:35.290 And now look at the pencil in the dry, 00:05:35.290 --> 00:05:38.510 when it looks as straight as it actually is. 00:05:38.510 --> 00:05:40.420 Can you tell any difference between the 00:05:40.420 --> 00:05:43.510 subjective quality of one experience and the other? 00:05:43.510 --> 00:05:48.510 Does one scene look, say, follier to you, or less clear, or more vivid? 00:05:48.510 --> 00:05:53.510 Philosophers who find they cannot grow aware of any such difference like to 00:05:53.510 --> 00:05:58.610 conclude that we must be aware of the same kind of thing in both cases. 00:05:58.610 --> 00:06:02.100 So, if we are directly aware of a subjective sense-datum 00:06:02.100 --> 00:06:04.340 in the case of non-veridical perception, 00:06:04.340 --> 00:06:07.060 such a sense-datum is what we are directly aware of 00:06:07.060 --> 00:06:09.950 also in the case of veridical perception. 00:06:09.950 --> 00:06:12.860 When we use our eyes, all we are ever 00:06:12.860 --> 00:06:15.610 directly aware of are subjective sense-data. 00:06:15.610 --> 00:06:19.530 By sight, we are never directly aware of physical objects. 00:06:19.530 --> 00:06:22.370 As we look around ourselves, we are cut 00:06:22.370 --> 00:06:24.460 off from the physical objects in our environment 00:06:24.460 --> 00:06:27.300 by a veil of subjective sense-data. 00:06:27.300 --> 00:06:30.130 Other variants of the argument establish 00:06:30.130 --> 00:06:35.690 analogous conclusions about the other senses: hearing, smell, taste, and touch. 00:06:35.690 --> 00:06:39.300 Some other arguments, including arguments from hallucination, 00:06:39.300 --> 00:06:42.430 lead from different premises to the same conclusions. 00:06:42.430 --> 00:06:46.020 These conclusions seem to clash with common sense. 00:06:46.020 --> 00:06:50.630 Surely, when we look at tables and chairs, we see these public, stable, 00:06:50.630 --> 00:06:53.140 physical objects without further ado. 00:06:53.140 --> 00:06:55.940 Surely, these objects are not blocked 00:06:55.940 --> 00:06:59.940 from view by subjective, ever-changing objects of awareness. 00:06:59.940 --> 00:07:03.800 Surely, we can just see tables and chairs, 00:07:03.800 --> 00:07:07.839 without having to infer their presence around us from 00:07:07.839 --> 00:07:12.010 subjective images, sense-data, or what have you. 00:07:12.010 --> 00:07:15.680 By leading to a conclusion that clashes with our common sense conception 00:07:15.680 --> 00:07:17.749 of perception, all these arguments 00:07:17.749 --> 00:07:22.089 confront us with what is often simply called the "problem of perception." 00:07:22.089 --> 00:07:24.780 We don't doubt that things sometimes 00:07:24.780 --> 00:07:27.780 appear elliptical, yellow, bitter, or rough 00:07:27.780 --> 00:07:32.010 when they actually are round, white, sweet, or smooth. 00:07:32.010 --> 00:07:33.930 The present argument suggests 00:07:33.930 --> 00:07:36.160 this implies that we cannot just see 00:07:36.160 --> 00:07:41.180 or hear, smell or taste, or feel the things around us 00:07:41.180 --> 00:07:45.660 This raises the problem: how is it possible for us to just see, or 00:07:45.660 --> 00:07:48.790 otherwise perceive, the things in our physical environment 00:07:48.790 --> 00:07:51.810 if these things often appear different than they are?