1 00:00:10,470 --> 00:00:15,380 So you can see this is in many ways a very modern vision. 2 00:00:15,380 --> 00:00:24,660 There is no surprise that Hume, out of all the philosophers of this period, is the philosopher who tends to speak most to the modern predicament. 3 00:00:24,660 --> 00:00:34,890 We live in a world in which people do think that the right way to understand human beings is as part of the natural world. 4 00:00:34,890 --> 00:00:40,640 Looking back to the 17th and 18th centuries, it's vitally important when you read the philosophy, 5 00:00:40,640 --> 00:00:45,720 the philosophers of that period, not to forget the elephant in the room. 6 00:00:45,720 --> 00:00:55,780 God. Almost every philosophical discussion of the period is informed by religious concerns. 7 00:00:55,780 --> 00:01:00,070 They're often not overt. It's often not easy to see them. 8 00:01:00,070 --> 00:01:06,100 But behind it all lies these fundamental changes. 9 00:01:06,100 --> 00:01:15,040 An earthquake that's going on in the foundations of the view of man and the universe and. 10 00:01:15,040 --> 00:01:22,010 The threat of Athie ism, the threat of heterodoxy. 11 00:01:22,010 --> 00:01:27,740 That lies behind a lot of the concerns that the philosophers of the period have. 12 00:01:27,740 --> 00:01:31,820 So here's a very simplistic big picture. 13 00:01:31,820 --> 00:01:38,990 You go back to the mediaeval period, physics is governed by natural motions, natural motions that have been put into things by God. 14 00:01:38,990 --> 00:01:49,810 God has created stone so that they naturally tend towards the centre of the world planet, which naturally tend to want to move in circles. 15 00:01:49,810 --> 00:01:55,150 That's replaced in the early modern period by a picture of inert matter, mechanical causation. 16 00:01:55,150 --> 00:02:02,920 Things do what they do because of forces acting on them rather than anything like desire's acting within them. 17 00:02:02,920 --> 00:02:10,720 Morality in the mediaeval period is based on revealed truth and natural law. 18 00:02:10,720 --> 00:02:21,530 We can go to the Bible. We can apply our reason. To that to the lessons that we learnt from that. 19 00:02:21,530 --> 00:02:25,200 But in the early modern period, that consensus gets undermined. 20 00:02:25,200 --> 00:02:35,970 We now no longer whether know whether we should seek authority in the church traditions or in the in the individual's reaction to the Bible. 21 00:02:35,970 --> 00:02:43,810 So. Can we base morality on Revelation when people interpret the revelation in different ways? 22 00:02:43,810 --> 00:02:52,720 Can reason fill the void? Should we, like Hume, rely on moral sense or feeling? 23 00:02:52,720 --> 00:03:01,920 Likewise, in politics, in the mediaeval world, we have the divinely ordained king who should be obeyed for that reason. 24 00:03:01,920 --> 00:03:06,540 Confidence in that authority is undermined, not least through the religious wars. 25 00:03:06,540 --> 00:03:12,180 And so we get a crisis of authority in politics. How is that to be filled? 26 00:03:12,180 --> 00:03:15,810 An appeal to natural right reason. Contract. 27 00:03:15,810 --> 00:03:23,700 Hobbs wanted to say that the way to do it is all to get together and make a social contract, erect a sovereign and then obey the sovereign. 28 00:03:23,700 --> 00:03:27,330 In order to avoid civil war. 29 00:03:27,330 --> 00:03:38,100 So you can see that the picture I gave in the first lecture of the crisis that affected the whole intellectual world in the early modern period, 30 00:03:38,100 --> 00:03:43,830 we can see that those of problems that echo down to this day. 31 00:03:43,830 --> 00:03:50,280 And this is why so many of the problems that we discuss within this course remain of relevance, 32 00:03:50,280 --> 00:04:01,110 even though the scientific theories that we have now seem to be a long way away from those that were around in the early modern period for us, 33 00:04:01,110 --> 00:04:07,790 just like them. It seems that the world differs radically from how it appears. 34 00:04:07,790 --> 00:04:16,460 Our best theory of the world attributes primary qualities to bodies with secondary qualities explained through a representative theory of perception. 35 00:04:16,460 --> 00:04:24,680 As we've seen in the early modern period, the idea that matter is made of little corpuscles, very different from what we see. 36 00:04:24,680 --> 00:04:30,620 We may see something as a particular colour. We may see a tree as brown. 37 00:04:30,620 --> 00:04:40,250 But actually, what's really there, we think, is little corpuscles whose arrangement gives rise to the sensation of Brown in our eyes, 38 00:04:40,250 --> 00:04:44,600 the reality and what we see are very different. Okay. 39 00:04:44,600 --> 00:04:49,280 Our modern theory attributes different properties to the actual matter of the tree. 40 00:04:49,280 --> 00:04:53,960 But the same problem is there. And this invites scepticism. 41 00:04:53,960 --> 00:05:01,970 If we can't trust our natural faculties to yield truth directly, we can't trust them to show us how things really are. 42 00:05:01,970 --> 00:05:11,850 Then how can we know how they are? Again, if the actions of body are explained mechanically, how does mind? 43 00:05:11,850 --> 00:05:16,650 As science grows in the early modern period through a purely mechanistic science. 44 00:05:16,650 --> 00:05:20,430 Now we have more sophisticated stuff like quantum mechanics. OK. 45 00:05:20,430 --> 00:05:28,380 It's not purely deterministic in the way that those early theories were. But it yields a very similar problem. 46 00:05:28,380 --> 00:05:36,780 If we think of ourselves as part of the natural world as constituted by material bodies and brain and so forth, 47 00:05:36,780 --> 00:05:47,010 then how does the action of that physical matter tie in with our view of our minds? 48 00:05:47,010 --> 00:05:49,350 And in particular, free will. 49 00:05:49,350 --> 00:06:00,570 How can we be free if all of our actions are the actions of bodies which are themselves determined or at least condition by physical laws, 50 00:06:00,570 --> 00:06:10,740 can free will actually make it make any sense? And if one believes in immortality and divine reward and punishment, how can that make any sense? 51 00:06:10,740 --> 00:06:15,000 That's a particular problem because of personal identity. 52 00:06:15,000 --> 00:06:22,350 If we think of ourselves as constituted as part of nature by material bodies and brains and so forth, 53 00:06:22,350 --> 00:06:32,900 does personal identity over time become something that's applicable at all, particularly in the context of religion? 54 00:06:32,900 --> 00:06:43,520 Well. We shall see that these sorts of debates echo through those topics in general philosophy, 55 00:06:43,520 --> 00:06:49,970 and I hope that when we study those in a bit more detail, you will see how they tie together. 56 00:06:49,970 --> 00:06:58,290 All as part of this crisis, which is very much the legacy of the early modern period. 57 00:06:58,290 --> 00:07:10,470 Okay, I'm just going to end with a brief comment about what happened after the early modern period. 58 00:07:10,470 --> 00:07:18,770 Well, we saw Hume leaving us with a rather. Unsettling picture of human nature. 59 00:07:18,770 --> 00:07:23,090 Humans. Part of the animal world. Not nearly as clever as they thought. 60 00:07:23,090 --> 00:07:29,960 They were reliant on brute animal instinct to find out about the world. 61 00:07:29,960 --> 00:07:34,490 Quite incapable of knowing about things. By pure reason. 62 00:07:34,490 --> 00:07:42,670 Then along came Emmanuel Kant. Very famous philosopher. 63 00:07:42,670 --> 00:07:50,290 Kempt started from the premise that Hume has to be wrong. Why does Hume have to be wrong? 64 00:07:50,290 --> 00:07:58,460 Well, Camp thought that there are certain things that we do know about the world with absolute and complete certainty. 65 00:07:58,460 --> 00:08:11,300 Here is some of them. We know with certainty, according to Kent, that the world has to be governed by universal causation. 66 00:08:11,300 --> 00:08:20,570 We know, according to Kent, that the principles of Euclidian geometry are utterly and completely certain. 67 00:08:20,570 --> 00:08:28,310 For example, the square on the hypotenuse of a right angle triangle is equal to the sum of the squares of the other two sides. 68 00:08:28,310 --> 00:08:37,560 We can prove it. We can prove it by pure logic. That is a truth about the world that we know with absolute certainty. 69 00:08:37,560 --> 00:08:43,090 And what about Newtonian mechanics? For example, the law of conservation of momentum? 70 00:08:43,090 --> 00:08:47,200 That has such a natural, elegant simplicity to it. 71 00:08:47,200 --> 00:08:54,610 According to Kant, this, again, is a principle that we can know to be true a priori eye of the world. 72 00:08:54,610 --> 00:09:03,390 We can know simply by applying our pure reason that these things are all true of the world. 73 00:09:03,390 --> 00:09:13,620 It follows that Hume must be wrong because if Hume is right, then it isn't possible to apply our pure reason to know things about the world. 74 00:09:13,620 --> 00:09:21,030 Kent developed a very elaborate theory to explain how it was that Hume could be wrong, according to Kent. 75 00:09:21,030 --> 00:09:29,610 Our minds condition the way the world appears to us. And so we can know a priori by how the world will appear. 76 00:09:29,610 --> 00:09:34,230 The phenomenal world that is the world that we experience must, for example, 77 00:09:34,230 --> 00:09:42,740 satisfy the axioms of Euclidean geometry because our minds themselves constitute it in such a way. 78 00:09:42,740 --> 00:09:51,200 Very interesting theory. Unfortunately, its premises are completely wrong. 79 00:09:51,200 --> 00:09:56,490 So let's look at what happened after Kent. 80 00:09:56,490 --> 00:10:02,940 Darwin's on the Origin of Species, 1859. A stronger confirmation, as one could wish. 81 00:10:02,940 --> 00:10:12,790 That we are indeed part of nature, not above it. Einstein's Theory of General Relativity, 1915. 82 00:10:12,790 --> 00:10:24,440 Space, it seems, is gravitationally curved. Euclid's axioms probably aren't true of the actual world after all. 83 00:10:24,440 --> 00:10:26,960 At any rate, they're certainly not knowable a priori, 84 00:10:26,960 --> 00:10:34,730 I can turn all these others had assumed that geometry does give us pure insight into the way the world is. 85 00:10:34,730 --> 00:10:43,430 It seems that that is not the case. The logical deductions that we make from the axioms may be fine if the axioms are true of the world, 86 00:10:43,430 --> 00:10:48,260 but we've no way of knowing a priori that they are true of the world. 87 00:10:48,260 --> 00:10:53,800 And then we get quantum mechanics in 1925. Or thereabouts. 88 00:10:53,800 --> 00:10:56,830 It was quite some long development. 89 00:10:56,830 --> 00:11:07,000 Undermining the idea that the world is law governed in the way that Kant thought and severely undermining the idea that it is intelligible. 90 00:11:07,000 --> 00:11:17,020 And I'm just going to give you a brief illustration of this. So this is a computer model of the famous two slit experiment. 91 00:11:17,020 --> 00:11:26,400 Here you have a light source at the bottom. And here you have a screen with two slips in it, very small slits. 92 00:11:26,400 --> 00:11:38,670 The light travels through these slits. And then at the far end here we have a screen on which we see where the light has fallen. 93 00:11:38,670 --> 00:11:46,470 And in what intensity and what you can see here is that you get this interesting pattern. 94 00:11:46,470 --> 00:11:55,160 Why does that pattern occur? Well, it seems that light has a wave form. 95 00:11:55,160 --> 00:12:04,430 So if I do this, you can now see how you're getting an interference pattern. 96 00:12:04,430 --> 00:12:11,420 You've got waves going out from each of the slits and where they meet, they interfere with each other. 97 00:12:11,420 --> 00:12:18,890 Just like ripples on a pond. If you drop two stones into a pond and you get the ripples coming from each of them, 98 00:12:18,890 --> 00:12:23,480 wherever the ripples coincide, they're both high or they're both low. 99 00:12:23,480 --> 00:12:31,600 The combination of the two will be even higher or lower. But at other points, you'll get an upward ripple, combining with a downward ripple. 100 00:12:31,600 --> 00:12:36,260 And the two will cancel out. So you get an interference pattern. Light. 101 00:12:36,260 --> 00:12:46,890 It seems, is constituted by waves. All well and good, but. 102 00:12:46,890 --> 00:12:49,530 If that pattern was a result of interference, 103 00:12:49,530 --> 00:13:00,180 then presumably what we can do is get rid of the interference by firing single particles of light single photons at the screen. 104 00:13:00,180 --> 00:13:09,600 So what I've done now, I've put a detector on the left slit and a detector at the right slits, and I'm going to fire individual photons at the screen. 105 00:13:09,600 --> 00:13:21,210 Let's do that. So I want to show these on the screen. 106 00:13:21,210 --> 00:13:23,550 So here we are. I'm firing them. 107 00:13:23,550 --> 00:13:30,880 You can see that the photons are going randomly through the two detectors and then they're ending up randomly on the screen. 108 00:13:30,880 --> 00:13:46,470 Now, let's speed that up and see what happens. 109 00:13:46,470 --> 00:13:55,260 So what we now have is individual photons going to the screen, the ones that get through either go through the left slit or the right slit. 110 00:13:55,260 --> 00:14:06,850 Then they go on to hit the screen at the back. And you can see that the interference pattern has completely disappeared. 111 00:14:06,850 --> 00:14:14,600 Fine. All nice, straightforward, we understand pretty much what's going on. 112 00:14:14,600 --> 00:14:21,140 But let's try that again. Except this time I'll take the detector's away. 113 00:14:21,140 --> 00:14:40,010 So now I'm firing individual photons at the screen, as you see. Let's do it repeatedly. 114 00:14:40,010 --> 00:14:47,260 How weird. What on earth is going on? 115 00:14:47,260 --> 00:14:55,590 If we fire the individual photons and have detectors at the slips to find out which way each photon went. 116 00:14:55,590 --> 00:14:59,460 The interference pattern disappears. 117 00:14:59,460 --> 00:15:09,180 If we then take the detectors away, we're still firing individual photons one at a time, but we no longer know which slip they're going through. 118 00:15:09,180 --> 00:15:17,900 Somehow the photons still end up ending up on the screen in an interference pattern. 119 00:15:17,900 --> 00:15:23,800 How can that possibly be? How can there being two slits rather than one? 120 00:15:23,800 --> 00:15:26,320 Make a difference to where the photon goes? 121 00:15:26,320 --> 00:15:34,600 If when you put a detector there, you only ever find the detector going through one slip rather than the other. 122 00:15:34,600 --> 00:15:40,120 It's seriously weird. Seriously, seriously weird. 123 00:15:40,120 --> 00:15:45,170 Now you can do the mathematics to find out what's going on. 124 00:15:45,170 --> 00:15:54,710 You can show that if you put a detector on, either slit the wave, the wave probability function changes. 125 00:15:54,710 --> 00:16:00,960 But that's not explaining why it happens. It's just saying this is the way it does happen. 126 00:16:00,960 --> 00:16:11,420 And I think quantum mechanics is a beautiful example of how humans approach to science has turned out to be right rather than Kentz. 127 00:16:11,420 --> 00:16:17,540 It seemed when Newton came out with the beautiful mathematics of his prankish here. 128 00:16:17,540 --> 00:16:23,320 But we were getting real insight into the way the will the way the world works and why it works that way. 129 00:16:23,320 --> 00:16:33,880 It all seemed to be so logical. And yet, as modern science has gone on, we found that trying to understand why it works as it does. 130 00:16:33,880 --> 00:16:39,670 Is a dead end. We have to make do with codifying how it works. 131 00:16:39,670 --> 00:16:47,130 Not why does it? OK. 132 00:16:47,130 --> 00:17:02,610 Incidentally, if you want to find out more about the stuff I'd been talking about in these first two and a half lectures. 133 00:17:02,610 --> 00:17:08,190 You might be interested to look at the introduction to my edition of Hume's enquiry, 134 00:17:08,190 --> 00:17:12,830 in which I give quite a lots of more detail on on all of this stuff. 135 00:17:12,830 --> 00:17:18,933 I didn't know how that little a little subliminal bit got in.