1 00:00:00,000 --> 00:00:05,840 (intro music) 2 00:00:05,840 --> 00:00:08,270 Hi! I'm Eugen Fischer, senior lecturer in 3 00:00:08,270 --> 00:00:10,410 philosophy at the University of East Anglia. 4 00:00:10,410 --> 00:00:13,170 Today, we will look at some paradoxes about perception, 5 00:00:13,170 --> 00:00:15,270 known as "arguments from illusion." 6 00:00:15,270 --> 00:00:19,850 These arguments ask us to consider cases of non-veridical perception, 7 00:00:19,850 --> 00:00:22,509 where something appears different than it is. 8 00:00:22,509 --> 00:00:28,330 For example, when we look at round coins sideways, they appear elliptical. 9 00:00:28,330 --> 00:00:31,720 Similarly, when seen from a greater distance, a man may 10 00:00:31,720 --> 00:00:35,500 seem less than half as tall as another man of roughly equal height. 11 00:00:35,500 --> 00:00:38,180 Or consider the phenomenon known as "refraction." 12 00:00:38,180 --> 00:00:40,160 When a straight straw is partially 13 00:00:40,160 --> 00:00:42,359 immersed in water, it looks bent. 14 00:00:42,359 --> 00:00:45,029 All of these facts are familiar from daily life. 15 00:00:45,029 --> 00:00:47,079 None of them is normally contested. 16 00:00:47,079 --> 00:00:50,510 But these familiar facts seem to have a striking consequence. 17 00:00:50,510 --> 00:00:53,120 They seem to imply that we are cut off from the 18 00:00:53,120 --> 00:00:57,030 physical objects around us by a veil of experience within us. 19 00:00:57,030 --> 00:01:01,240 The eighteenth-century philosopher David Hume drew this consequence very swiftly 20 00:01:01,240 --> 00:01:03,699 when reflecting on another relevant fact: 21 00:01:03,699 --> 00:01:07,189 as we all know, the table look smaller and smaller to people 22 00:01:07,189 --> 00:01:09,030 the further away the move from it. 23 00:01:09,030 --> 00:01:11,790 Hume observes that the table we see seems to 24 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 25 00:01:16,500 --> 00:01:20,760 real table, which is made of wood and stands in the parlor, regardless of 26 00:01:20,760 --> 00:01:22,480 whether we look at it or not. 27 00:01:22,480 --> 00:01:25,880 Hume immediately infers that we cannot be aware of this 28 00:01:25,880 --> 00:01:30,280 unchanging, real table, and therefore must be aware of something else. 29 00:01:30,280 --> 00:01:34,130 He concludes that thing we see is an image of the table, 30 00:01:34,130 --> 00:01:37,990 whose size does change as we move away from the table. 31 00:01:37,990 --> 00:01:41,090 This image then is present to us in our minds. 32 00:01:41,090 --> 00:01:43,629 In other words, when you look at the table, 33 00:01:43,639 --> 00:01:48,239 you are only aware of a mental image, not of the physical table. 34 00:01:48,239 --> 00:01:51,950 To unpack this rather swift but historically influential argument, 35 00:01:51,950 --> 00:01:53,790 let's have a closer look at the case of 36 00:01:53,790 --> 00:01:58,090 the round coin that appears elliptical to you when you look at it sideways. 37 00:01:58,090 --> 00:02:00,520 What exactly are you aware of in this case? 38 00:02:00,520 --> 00:02:02,100 Describe your experience, rather than the objects around you. 39 00:02:02,100 --> 00:02:05,450 Describe what you are aware of, 40 00:02:05,450 --> 00:02:09,610 without making any judgment about the physical object you're facing, without 41 00:02:09,610 --> 00:02:12,480 judging that object's shape, or size, 42 00:02:12,480 --> 00:02:14,830 or color, or any other property of it. 43 00:02:14,830 --> 00:02:17,009 That the right thing to say then, it seems, 44 00:02:17,009 --> 00:02:20,870 is that you're aware of an elliptical, golden patch. 45 00:02:20,870 --> 00:02:23,870 This judgment is often called the "phenomenal judgment." 46 00:02:23,870 --> 00:02:26,570 The first step the argument elicits such 47 00:02:26,570 --> 00:02:28,829 phenomenal judgments about cases of 48 00:02:28,829 --> 00:02:32,870 non-veridical perception, like that of the coin or Hume's table. 49 00:02:32,870 --> 00:02:37,149 The second step has us figure out what kind of thing we're then aware of. 50 00:02:37,149 --> 00:02:39,579 What could that elliptical patch be? 51 00:02:39,579 --> 00:02:43,669 It cannot be the coin, because the coin is round and not elliptical. 52 00:02:43,669 --> 00:02:47,339 So you're clearly aware of something other than the coin. 53 00:02:47,339 --> 00:02:50,189 Hume called this other thing an "image." 54 00:02:50,189 --> 00:02:54,569 A now more common, and more neutral term, is "sense-datum." 55 00:02:54,569 --> 00:02:56,969 Now continue to look in the direction of the coin. 56 00:02:56,969 --> 00:02:58,939 How many different things do you see? 57 00:02:58,939 --> 00:03:01,159 How many different things can you direct your 58 00:03:01,159 --> 00:03:03,690 attention at and say that you are aware of? 59 00:03:03,690 --> 00:03:07,560 Clearly, you cannot first direct your attention at something elliptical and 60 00:03:07,560 --> 00:03:09,960 then shift your attention elsewhere to 61 00:03:09,960 --> 00:03:13,560 become aware of something else that could be the coin. 62 00:03:13,560 --> 00:03:16,669 So you are aware only of one thing, not of two. 63 00:03:16,669 --> 00:03:20,439 We already concluded that you are aware the sense-datum. 64 00:03:20,439 --> 00:03:23,239 Therefore, you cannot be aware of the coin too. 65 00:03:23,259 --> 00:03:27,099 At any rate, not in the same way or sense. 66 00:03:27,099 --> 00:03:31,379 But of course you are aware of the coin in some sense. 67 00:03:31,379 --> 00:03:33,369 You know perfectly well that you are 68 00:03:33,369 --> 00:03:37,139 looking at a coin rather than, say, a marble or a dice. 69 00:03:37,139 --> 00:03:41,629 Proponents of the argument from illusion therefore commonly called the cautious 70 00:03:41,629 --> 00:03:45,560 conclusion that the subjective sense-datum is the only thing you are directly aware of 71 00:03:45,560 --> 00:03:48,200 when looking at the coin sideways. 72 00:03:48,200 --> 00:03:51,440 At the same time, you may be indirectly 73 00:03:51,440 --> 00:03:53,669 aware of the physical object, namely, 74 00:03:53,669 --> 00:03:57,649 in virtue of being directly aware of the sense-datum. 75 00:03:57,649 --> 00:04:00,949 So far, we have rehearsed the first half of the argument. 76 00:04:00,949 --> 00:04:05,480 The second half then generalizes from the particular case of non-veridical 77 00:04:05,480 --> 00:04:08,509 perception to all cases of perception. 78 00:04:08,509 --> 00:04:10,989 This generalizing step builds on the 79 00:04:10,989 --> 00:04:13,120 observation that sense data and physical 80 00:04:13,120 --> 00:04:17,270 objects are the most radically different kinds of things. 81 00:04:17,270 --> 00:04:21,390 For a start, the sense-datum is rather less stable than the coin. 82 00:04:21,390 --> 00:04:24,990 The color patch changes its shape the moment you move, 83 00:04:24,990 --> 00:04:27,050 while the coin retains its shape. 84 00:04:27,050 --> 00:04:32,700 The sense-datum also vanishes the moment you close your eyes, while the coin vanishes 85 00:04:32,700 --> 00:04:34,910 only the moment it gets melted down, 86 00:04:34,910 --> 00:04:38,120 or some other major physical mishap occurs to it. 87 00:04:38,120 --> 00:04:43,300 So the sense-datum and its properties depend upon you, the observer, 88 00:04:43,300 --> 00:04:48,590 in ways in which the physical object and its properties do not. 89 00:04:48,590 --> 00:04:51,480 Sense data are subjective, ever-changing, 90 00:04:51,480 --> 00:04:55,860 and fleeting, like the flickering of a candle or its dying smoke. 91 00:04:55,860 --> 00:04:57,980 Physical objects, by contrast, are 92 00:04:57,980 --> 00:05:01,900 objective and stable, like solid tables and hard coins. 93 00:05:01,900 --> 00:05:04,300 the intuitive key assumption now is 94 00:05:04,300 --> 00:05:07,980 that our awareness of such radically different things should 95 00:05:07,980 --> 00:05:11,140 constitute qualitatively different experiences. 96 00:05:11,140 --> 00:05:14,480 We should be able to tell from the subjective quality of our 97 00:05:14,480 --> 00:05:19,330 experience whether we are aware of a sense-datum or of a physical object. 98 00:05:19,330 --> 00:05:20,330 But compare. 99 00:05:20,330 --> 00:05:23,850 Have a look at this pencil, which is partially immersed in water. 100 00:05:23,850 --> 00:05:26,220 To most people, it seems bent. 101 00:05:26,220 --> 00:05:28,850 If you are like them, you are now directly 102 00:05:28,850 --> 00:05:33,060 aware of a sense-datum or color patch, which actually is bent. 103 00:05:33,060 --> 00:05:35,290 And now look at the pencil in the dry, 104 00:05:35,290 --> 00:05:38,510 when it looks as straight as it actually is. 105 00:05:38,510 --> 00:05:40,420 Can you tell any difference between the 106 00:05:40,420 --> 00:05:43,510 subjective quality of one experience and the other? 107 00:05:43,510 --> 00:05:48,510 Does one scene look, say, follier to you, or less clear, or more vivid? 108 00:05:48,510 --> 00:05:53,510 Philosophers who find they cannot grow aware of any such difference like to 109 00:05:53,510 --> 00:05:58,610 conclude that we must be aware of the same kind of thing in both cases. 110 00:05:58,610 --> 00:06:02,100 So, if we are directly aware of a subjective sense-datum 111 00:06:02,100 --> 00:06:04,340 in the case of non-veridical perception, 112 00:06:04,340 --> 00:06:07,060 such a sense-datum is what we are directly aware of 113 00:06:07,060 --> 00:06:09,950 also in the case of veridical perception. 114 00:06:09,950 --> 00:06:12,860 When we use our eyes, all we are ever 115 00:06:12,860 --> 00:06:15,610 directly aware of are subjective sense-data. 116 00:06:15,610 --> 00:06:19,530 By sight, we are never directly aware of physical objects. 117 00:06:19,530 --> 00:06:22,370 As we look around ourselves, we are cut 118 00:06:22,370 --> 00:06:24,460 off from the physical objects in our environment 119 00:06:24,460 --> 00:06:27,300 by a veil of subjective sense-data. 120 00:06:27,300 --> 00:06:30,130 Other variants of the argument establish 121 00:06:30,130 --> 00:06:35,690 analogous conclusions about the other senses: hearing, smell, taste, and touch. 122 00:06:35,690 --> 00:06:39,300 Some other arguments, including arguments from hallucination, 123 00:06:39,300 --> 00:06:42,430 lead from different premises to the same conclusions. 124 00:06:42,430 --> 00:06:46,020 These conclusions seem to clash with common sense. 125 00:06:46,020 --> 00:06:50,630 Surely, when we look at tables and chairs, we see these public, stable, 126 00:06:50,630 --> 00:06:53,140 physical objects without further ado. 127 00:06:53,140 --> 00:06:55,940 Surely, these objects are not blocked 128 00:06:55,940 --> 00:06:59,940 from view by subjective, ever-changing objects of awareness. 129 00:06:59,940 --> 00:07:03,800 Surely, we can just see tables and chairs, 130 00:07:03,800 --> 00:07:07,839 without having to infer their presence around us from 131 00:07:07,839 --> 00:07:12,010 subjective images, sense-data, or what have you. 132 00:07:12,010 --> 00:07:15,680 By leading to a conclusion that clashes with our common sense conception 133 00:07:15,680 --> 00:07:17,749 of perception, all these arguments 134 00:07:17,749 --> 00:07:22,089 confront us with what is often simply called the "problem of perception." 135 00:07:22,089 --> 00:07:24,780 We don't doubt that things sometimes 136 00:07:24,780 --> 00:07:27,780 appear elliptical, yellow, bitter, or rough 137 00:07:27,780 --> 00:07:32,010 when they actually are round, white, sweet, or smooth. 138 00:07:32,010 --> 00:07:33,930 The present argument suggests 139 00:07:33,930 --> 00:07:36,160 this implies that we cannot just see 140 00:07:36,160 --> 00:07:41,180 or hear, smell or taste, or feel the things around us 141 00:07:41,180 --> 00:07:45,660 This raises the problem: how is it possible for us to just see, or 142 00:07:45,660 --> 00:07:48,790 otherwise perceive, the things in our physical environment 143 00:07:48,790 --> 00:07:51,810 if these things often appear different than they are?