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Lesson 1.4: The Method of Doubt
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Descartes responds to radical uncertainty with an audacious plan: find one belief so secure that nothing—not even deception itself—can shake it.
Topics Discussed:- The historical and intellectual crises of early 17th-century Europe that shaped Descartes’ project
- The motivation behind Descartes’ method of doubt as a response to skepticism
- The regress problem and why it pressures philosophers toward foundationalism
- Descartes’ strategy of withholding belief from anything that can be doubted
- Arguments from sense deception, dreaming, and the evil demon
- Why even mathematics and logic become targets of radical doubt
- The search for indubitable foundations as the starting point for knowledge
- How Descartes’ internal, first-person approach marks a turning point in modern epistemology
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Transcript
Pragmatic Knowledge in the 17th Century
00:00:03
Speaker
We have in the past considered the Baconian approach to knowledge. So that is when we assume that the ancient take on knowledge, this idea that you need rock solid justifications that can stop any kind of skeptical argumentation.
00:00:27
Speaker
Francis Bacon says, yeah, forget all that noise. that We don't need to do that at all. The way that Bacon conceived of knowledge is much more pragmatic.
00:00:39
Speaker
What is knowledge? It's information that you can apply in practice. Information that can help you alleviate human suffering. So if you like that, well then, hey, maybe you're a Baconian.
00:00:57
Speaker
But you know what? There are other views around in the 1600s in Western Europe. Maybe take a look at some of those first before we really make up our mind here. So today we're going to look at or begin to look at the view of a man named Rene Descartes.
00:01:20
Speaker
And in fact, today we'll look at his negative project when he's kind of taking apart
Epistemic Crisis: Then and Now
00:01:26
Speaker
beliefs. So We'll do that. But before we get into that, I want to set this up a little bit with some historical context. I really am stressing historical context.
00:01:41
Speaker
And i think I have good reasons for it here. Listen up. and Tell me if you think this is a good idea. so If I don't remind you that we are in the middle of an epistemic crisis here in the 17th century, it looks like worrying about skepticism. It's just like a game that epistemological philosophers play when they're quote unquote doing philosophy.
00:02:13
Speaker
Because if you, you know, live in a time where you feel that knowledge is secure and, you know, we know what we know and it's not going to really change, then yeah, skepticism kind of looks like, you know, pastime.
00:02:33
Speaker
Arguing against skepticism looks like a pastime. So maybe that's true for you. Maybe you think that everything is hunky-dory right now, epistemically speaking.
00:02:46
Speaker
Let me, I guess I'll make a comment about that in a second. But in the 1600s, as I've stressed over and over again, that is not the case, right? They are moving away from the Aristotelian worldview.
00:03:02
Speaker
And that was, you know, the way that everyone thought for like 2000 years, And so it's going to be a little bit unnerving to say, okay, well, okay, now how how do we think about knowledge? So that was going on.
00:03:21
Speaker
And let me make my comment here. Some people think that we are currently, once again, going through an epistemic crisis.
00:03:33
Speaker
What is knowledge now, right? Let me give you some buzzwords, fake news, alternative facts. What really does make what we know justified?
00:03:47
Speaker
What justifies our knowledge claims? How come some people can say, Well, I believe this because of this. And you think that that is like a conspiracy theory.
00:03:58
Speaker
So how can we ground our conception of knowledge so that it can resolve the tensions that we, i think a lot of us feel right now. Some people think certain things are facts.
00:04:12
Speaker
And, ah you know, it seems to not be a fact. So maybe we are currently in an epistemic crisis of our own. And so you can kind of you know, sympathize with what was going on in the sixteen hundreds They weren't sure what counts as knowledge anymore. Everything is okay, epistemically speaking. If everything is okay, epistemically speaking, you don't really think about this.
00:04:42
Speaker
But when you can't agree on what the truth is, well, that's when, okay, so how do we know what we know? That's when these questions really start.
00:04:53
Speaker
Okay, well, that's one point that I wanted to make. Here's another one.
Societal Challenges and Shared Knowledge
00:05:00
Speaker
I think it'll, you know, it's adjacent, but in the past, societal advancements were often accompanied by backtracking.
00:05:10
Speaker
And why is this relevant? Well, you know, again, if things are going honky dory, you don't really worry about like, how do you know what you know?
00:05:22
Speaker
But if things are not going great, then yeah, you want to know how do we fix it? And the way you come to a conclusion as to how you fix it is that you have to have the same shared epistemic norms.
00:05:40
Speaker
So I'll explain all that in a second. Let me talk about something that doesn't seem relevant, but I had a very crappy car when I was in my late teens. A high degree of crapulence, we might say.
00:05:53
Speaker
And i actually got quite good at fixing cars because of how bad my car was. And so what I mean by this is the fact that, you know, you keep coming into recurring problems actually makes it so that you learn how to fix things.
00:06:12
Speaker
Well, in a society where you have a lot of problems arising, you have to figure out how to come up with practical solutions on the fly, right? know You have to be ready for that kind of thing. And that's exactly what was happening, you know, honestly, through most of human history, new problems arise and they're really, really bad. And people have to figure out how do we how do we figure out a solution?
00:06:40
Speaker
In figuring out solutions, often entails, actually I'm going to say almost always entails in the very least, beginning with agreeing on what the facts of the matter are.
00:06:55
Speaker
And so epistemology was very relevant in the 17th century. And I'm going to go ahead and say it it's still relevant today, right?
00:07:07
Speaker
It's the case that whenever things aren't socially speaking ah very friendly, when there's hostility between different camps and different people ah hold on to different ways of believing and different sets of facts, what we have there is an epistemic conflict.
00:07:31
Speaker
And that's why epistemology is very useful. so We had spoken that we are in the Tudor period and for the most part that was a period of stability in England at least.
00:07:47
Speaker
But we have mentioned various times that this was also a time period where there was a kind of conflict, lots of religious conflict and persecution.
00:07:58
Speaker
One person we haven't spoken about before is Giordano Bruno.
Academic Freedom and Rational Discourse
00:08:04
Speaker
Bruno believed that not only did he accept the heliocentric model of the solar system, he also believed that the stars...
00:08:17
Speaker
are themselves suns that probably have their own planets orbiting them. And so there's probably other humans in those other, or not necessarily humans, but other living creatures on those planets revolving around those suns.
00:08:38
Speaker
And so very interesting ideas from Giordano Bruno over 400 years ago. Well, the authorities, the religious authorities of the time did not take kindly to his views because, well, it didn't line up with the Bible. He was burned at the stake.
00:08:59
Speaker
So that is something that I think, I hope anyone listening to this would say, yeah, you shouldn't, you shouldn't kill people for having different hypotheses than yours.
00:09:13
Speaker
ah academic freedom is something that you know basically makes the university system work and if someone had different ideas the way to respond to them is through rational argumentation through evidence that kind of thing so that is not good things are not honky dory another thing that was going on elsewhere in Europe is that famine struck in Russia.
00:09:40
Speaker
Famine has been a persistent problem for humanity for like, you know, i don't know if humans have been around 200,000 years, like been problem.
00:09:54
Speaker
six hundred years it's been a problem um There is a whole idea called the great escape where we finally escape from famine and disease and all that. So Russian famine strikes. It is very, very bad.
00:10:08
Speaker
And so people need to know what could we have done to avoid this? How do we know what we know, right? How do we know which plan of action can um you know successfully avoid this situation in the future? We've already mentioned the 30 Years War many, many times. This is obviously an atrocious conflict and it had a lot to do with beliefs, right? So some people had a certain set of beliefs about what it meant to be a Christian and other people had a different set of beliefs.
00:10:46
Speaker
And that's at least one of the reasons why they fought it out and millions died. So there is yet another problem that arises because of beliefs. And well, this one isn't necessarily because of beliefs or not as directly, at least. But let me just call this...
00:11:11
Speaker
a threat multiplier. the The thing with the plague, the bubonic plague, is that it keeps coming. It's always, it's if anyone's familiar here with the COVID-19 pandemic, it's not that you know it hits once and then it goes away. You build immunity and it goes away. now it's not like that. it It comes in waves. And so you can see in the COVID-19 pandemic that
00:11:42
Speaker
hospitalizations go up and then they go down. and so that's kind of the deal, right? It goes up and down and, you know, you have to live with that for a decade, decades sometimes.
00:11:55
Speaker
So that was the exact same thing with the bubonic plague. It would come, it would go. and that just makes things... you know there's ah There's an underlying tension to your existence. right So not not good for epistemic matters.
00:12:13
Speaker
Well, all of this was going on and so you can see that beliefs matter. Inquiring as to how it is that we form our beliefs, that matters.
00:12:26
Speaker
And so several philosophers and intellectuals began to focus on something that they felt they might be able to affect, right? They were thinking, okay, we had so many problems here.
00:12:40
Speaker
At least some of them are arising because of this. Religious convictions. So that is one thing that they began to try to
Descartes and Religious Critique
00:12:51
Speaker
address. Now we're going to talk about two people in particular, Rene Descartes and John Locke.
00:12:59
Speaker
Locke we will talk about in the next lesson. But what they were noticing is that Religious fanatics, they reasoned just as well as the best logicians.
00:13:11
Speaker
If you take a symbolic logic course, you learn about modus ponens and modus tollens. Well, they were able to make those kinds of arguments, these religious fanatics, just like anyone else, right? Just like a ah well-bred logician. So,
00:13:27
Speaker
What is going on here? What is the problem? Why do they arrive at such harmful and cruel conclusions, such as it is justified to harm people that don't believe exactly what I believe?
00:13:43
Speaker
Well, Descartes and Locke, in their own ways, realized that the problem was that people began with religious assumptions that they understood to be a universal truth. In other words, their logic was just fine.
00:14:02
Speaker
It's simply the case that they had some dogmas in there, some unquestioned truths that were mucking up the whole reasoning. If you start from dubious starting points, right? If you have in there really false beliefs that you cannot question, well, from there you are able to justify all kinds of horrible things like the killing of heretics, the torture of witches, and of course, holy war.
00:14:39
Speaker
And so this is how we're going to begin to get into the topic of today's lesson. The year, my friends, is 1640.
00:14:51
Speaker
And the person in question is René Descartes. So Descartes has many hats and most people that we'll be covering wear many hats because Well, there was no professional philosophers yet, right? That took some time. But um in this case, Descartes was a philosopher, a mathematician, a scientist.
00:15:18
Speaker
He was also a mercenary of sorts. He was a paid soldier that fought in one of the religious conflicts that we've talked about. I think he was ah in the artillery, which means that he would measure the trajectory of cannonballs and kind of help people aim the cannonballs.
00:15:37
Speaker
In any case, He is famous for a couple of things. I'm going to mention his Cartesian coordinates. If you ever took a geometry class, you know that there is the X and Y graph, right? Those are Cartesian coordinates. It's a way to combine algebra and geometry.
00:15:57
Speaker
so that's actually Descartes, right? He was very famous in his day for his mathematical accomplishments. He is also um going to provide for us a different epistemic theory, a new epistemic theory.
00:16:13
Speaker
So let's get into that right now.
00:16:19
Speaker
Let me begin with this. It's kind of an overall, you know, um eagle eye view of the Cartesian project. So Descartes believed that our premises must be more certain than our conclusions.
00:16:33
Speaker
What that means is that we must move from propositions that we have more confidence in to those that we have less confidence in, at least initially before argumentation.
00:16:45
Speaker
What does all that mean? Essentially, unlike the religious fanatics that Descartes was critiquing in his own way, he thinks you should start with not very dubious, you know, religious dogmas, but instead with things that you know for sure.
00:17:03
Speaker
And based on those things that you know for sure, you can establish your other beliefs. And that's how you justify your claims. You start with what you know 100% certainty then go from there Okay, that sounds great, right? So a very unique idea, maybe?
00:17:26
Speaker
Not quite.
Foundationalism and Knowledge Justification
00:17:27
Speaker
It's actually the case that Aristotle made a very similar point 2,000 years prior to this in a work known as the Posterior Analytics.
00:17:38
Speaker
That's why typically I refer to this principle as the, you know, the dictum of Aristotle or Aristotle's dictum. And I definitely think that we should kind of, you know, give credit to both of these thinkers because Aristotle, know,
00:17:54
Speaker
is using this principle in his own way for his own goals. What Descartes is doing is something very important here because he's taking these principles from from Aristotle and using them in novel ways for his historical context.
00:18:14
Speaker
So among the many things that Descartes is doing here, He's going to argue against circular reasoning. So what is that? what There's an informal fallacy known as begging the question. What that basically means, if I can give you a semi-formal definition, is whatever it is that you're trying to argue for, you basically just assume that it's true. Now that's obviously gobbledygook. sounds crazy to even try to argue in that way.
00:18:45
Speaker
Well, let me give you an example so you can see that sometimes people accidentally slip into this. So let's just say that someone says, hey, I believe that God exists. Very cool. There's a conclusion, right? So you ask them, what how do you how do you know that?
00:19:01
Speaker
Well, because it says so in the Bible, which is true. Okay, cool. All right. So because it says on the Bible and the Bible is true, that's how you know that God exists.
00:19:12
Speaker
Oh, and how do you know that what's in the Bible is true? And then they respond, oh, well, that's because it came from God who exists.
00:19:22
Speaker
In other words, you're justifying your belief that God exists through the Bible and you're justifying your belief in the Bible through God. So that is hopelessly circular reasoning. I hope you can tell.
00:19:37
Speaker
And not only is it circular reasoning, but it seems to be fairly evident that it's impossible to refute that. If you already believe those two things,
00:19:50
Speaker
and that's how you defend them, you're just going to go around in circles. So not only is your defense of it circuitous, but it might be the case that you're kind of stuck in a loop. There's no way to disconfirm what you believe.
00:20:04
Speaker
That's a more psychological point that I'm making there, but I don't know, it is true. Anyway, the point that I'm trying to make here is that Descartes is not an Aristotelian, but he is using Aristotelian ideas to paradoxically help overturn the Aristotelian worldview.
00:20:25
Speaker
And I love this, right? This is something that we see, you know, um throughout the history of philosophy, not only Western philosophy, Aztec philosophy, Eastern philosophy, whatever.
00:20:38
Speaker
You hear what wise people have to say and you're allowed to disagree, you know, but you don't toss it all out. You kind of mine through it for the good ideas and you keep those and you keep using them.
00:20:54
Speaker
And based on those good ideas that still, you know, stand up to rational scrutiny, you build off of those and that's how progress comes. So I like it. That's ah that's a really good thing there.
00:21:09
Speaker
Anyway, all of this has been very abstract. Let's get a little more concrete. I like to give metaphors whenever possible for you know philosophical projects.
00:21:20
Speaker
And if I had to give a metaphor for Descartes project, it's basically that of a building. Now, I hope you come up with your own metaphor for this.
00:21:30
Speaker
It will be very useful in your understanding. But I like the building because when you make a building or a house or whatever, you have to lay the foundation first and upon that foundation you build the rest of your house or building or whatever so here descartes is basically saying look for those beliefs that you know with certainty that's your foundation and then you can stack up the rest of your beliefs now if some beliefs don't end up fitting in that structure you're making well
00:22:06
Speaker
I don't know, don't believe those. But always start with what you know for sure. Okay, well then, if that metaphor works for you, and I hope it does, what is your foundation?
00:22:21
Speaker
How do you know those beliefs that you know for sure? For this, Descartes uses what is typically known as the method of doubt,
00:22:32
Speaker
AKA hyperbolic doubt. I kind of like that phrase, hyperbolic doubt. And his goal was to disabuse himself of anything he didn't know with absolute certainty.
00:22:46
Speaker
Okay. It's time to get technical. We want to have some jargon for all of this. So far, we've just kind of been speaking of it somewhat loosely.
00:22:58
Speaker
So the project in general, the ah approach, is known as foundationalism. And this is a view that some beliefs are foundational.
00:23:09
Speaker
They don't need to be justified. They are, in a way, self-justifying or self-evident or self-authenticating if you like these phrases.
00:23:24
Speaker
Basically, you don't need to justify them further. They they sort of you know, are, i don't want to say obvious, self-evident does kind of mean obvious, right?
00:23:36
Speaker
But they can serve as stops to the regress, right? You don't have to keep justifying these. These beliefs are just kind of where the buck stops, right? They're they're self-evident. You don't have to go any further.
00:23:51
Speaker
And it is upon these foundational beliefs that you can build up the rest your beliefs. And so this is how Descartes justifies knowledge claims.
00:24:03
Speaker
And in effect, what Descartes is doing is he's taking this idea from, you know, Plato, the JTB theory of knowledge, which Plato may or may not have believed,
00:24:17
Speaker
And, you know, that is vulnerable to skeptical argumentation. So what he does is provide a new take on how to justify claims that isn't vulnerable to the regress argument.
00:24:36
Speaker
So here is the infinite regress argument that we have covered in the past. And Descartes is basically blocking this argument by blocking premise number three.
00:24:49
Speaker
Premise number three reads, in order to just finally believe something, you must believe it on the basis of an infinite amount of good reasons.
00:25:01
Speaker
Well, Descartes is saying, nope, that's not true. There are some beliefs that you don't have to further justify. And if you get down to those beliefs, then you stop the infinite regress.
00:25:16
Speaker
Let's just say that you have belief A and they say, oh, the skeptics are here and they're like, yeah, Well, how do you know belief A? And you say, well, B, C, and D. And they ask, well, do you know B, C, and D?
00:25:29
Speaker
And you say say E through G and H through whatever, right? And then eventually you get to belief Z. And they say, well, how do you justify Z? And you say, well, Z is a foundational belief. It is self-evident.
00:25:45
Speaker
That's it. You can't question it. And you can even you know tell the skeptic, try to question this belief. How can you possibly doubt this?
00:25:56
Speaker
And hopefully you stump them and boom, the infinite regress is gone. Okay, the method of doubt is, well, here's what it might look like in practice. It's not exactly what Descartes did, but basically you consider a belief, whatever you want, um and then try to doubt it.
00:26:20
Speaker
And if that belief allows for any possibility of doubt, discard, toss. You don't need it. It is not a foundational belief.
00:26:32
Speaker
Repeat. a lot and whatever is left over at the end of all that, boom, that you know with certainty. That's a foundational belief.
00:26:46
Speaker
Let's go over examples of what are totally not foundational beliefs, right? This is, as I mentioned earlier, the destructive phase of Descartes philosophy.
00:26:59
Speaker
He's basically getting rid of beliefs right now. So we have ah the belief that I know where I parked my car. How about that? ah That is my car right there. As you can tell, I drive very expensive sports cars.
00:27:13
Speaker
I'm kidding. I don't. ah So let's pretend this is my car. and let's pretend that I'm saying to myself, I know where I parked my car. Now, if you have ever been mistaken about where you parked your car, even once,
00:27:30
Speaker
You cannot, at least rationally, be 100% certain as to where you parked your car. You have to ah allow for at least a little bit of doubt. At most, you can have like, i don't 99.4% confidence or something, right?
00:27:46
Speaker
So that is, and that's, that's for me. I hardly ever forget where I parked my car. My mom basically 100% of the time forgets where she parked the car. So it might depend on different people.
00:28:01
Speaker
Here is the point. You can't be a hundred percent certain that you know this. Everyone i'm suspecting has made that mistake at least once.
00:28:12
Speaker
Or how about this one? Do you know where your ID is? Maybe you do, maybe you don't. If you have ever misplaced your ID or thought you had it when you didn't, then that's not a foundational belief.
00:28:28
Speaker
I know where my ID is. That cannot be a foundational belief. Right. I actually know someone who tried to go somewhere where you have to be 20 to one and over and just forgot their ID like numerous times they've forgotten their IDs and can't get into where they want to get into.
00:28:45
Speaker
Where is your debit card? I know one person, me who went to the store grabbed a bunch of stuff and, you know was ready to ring him up only to realize that he, me, didn't have any way to pay for things. You're lucky now. Now you can basically pay for things with your smartphone. But back in those days, you needed actual money or some kind of, you know, card or cash or something. So if you've ever forgotten your ID or your debit card or
00:29:18
Speaker
where you parked your car, these can't be foundational beliefs. I hope you're noticing that basically if it's possible for you to be wrong about it and you've been wrong in the past, you can't call these foundational beliefs. They're not something that you know with 100% certainty.
00:29:35
Speaker
These are not the kind of thing that could serve as a foundational belief and i'm not sure that i would want to you know to right so how do you base the rest of your beliefs i know where my idea is like that's a ridiculous foundational belief right so not only are they not foundational beliefs but you wouldn't even want them to be they're kind of you know uh Just kind of whatever knowledge claims, not terribly important knowledge claims, non foundational knowledge claims. One more, why not?
00:30:09
Speaker
Do you know how much money is in your account right now?
00:30:13
Speaker
I can tell you with a high degree of confidence that I have no idea how much money I have in there. And you're probably the same. ah Even if you just checked, I've been wrong after I just checked. So ah that is also not a foundational belief. Nonetheless,
00:30:32
Speaker
You're getting the point. Descartes here is getting rid of most beliefs. He's saying, yeah, you know, that's not a foundation of belief. That is not not that, not that. Yeah. So he's going to keep continuing to do this.
00:30:44
Speaker
And eventually he would discover foundational beliefs. And it is upon those foundational beliefs that he will eventually build the rest of his worldview. As I mentioned earlier, though,
00:31:01
Speaker
He did not ah do this exactly the way that we went over right now. He was a little bit more judicious than that. He didn't go one belief at a time and you know discard or whatever.
00:31:15
Speaker
It was in you know big jumps that he took. And he did this through some very famous arguments. So let's move into those arguments now.
00:32:06
Speaker
So now we're going to move into Descartes' actual arguments. But I think I'm going to give you a little bit of context here because it'll help you understand them. At least um by the end of the next lesson, the historical context that I'm going to give you right now will be very, very helpful.
00:32:25
Speaker
So I guess that just means that we have to get into story time, right? Cool. Well, here are, i mentioned before that Aristotle was, you know, ah the Aristotelian worldview, I should say, was collapsing and Descartes definitely wanted to help bring that along in the sense that he was defending the new science, right? He he liked the new science.
00:32:58
Speaker
So that's definitely part of his project. Another reason, of course, that we already mentioned is that he thought some people had religious convictions, right? that were disastrously you know flawed and and leading to harm and leading to anti-scientific concerns.
00:33:19
Speaker
So that's another reason why he did that. And here are some other potential reasons. Once you see all the reasons that motivated Descartes to embark on his project, then you can really see, oh,
00:33:34
Speaker
Okay, I see what he's doing. Okay.
Reason, Religion, and Persecution
00:33:37
Speaker
So another thing that Descartes was probably doing, to be honest, is trying to avoid arrest. And while he was at it, oh, why the heck not? He was going to reconcile reason and religion so that being religious,
00:33:56
Speaker
is highly compatible with investigating the natural world, doing what he was doing, right? Mathematics, science, physics, whatever. So these are some other reasons why Descartes i engaged in the undertaking that he engaged in And to help talk about all of this, let's talk about Galileo Galilei.
00:34:23
Speaker
So Galileo is, i mean, the the man needs like no introduction, right? He is uber famous. And um you know what he defended. He defended the heliocentric model of the solar system.
00:34:40
Speaker
The dialogue or the work that we should talk about is his dialogue concerning two chief world systems. That is a dialogue in which he tries to popularize this heliocentric model.
00:34:57
Speaker
But Galileo was a little bit, how should I say this? He was a little um forceful and maybe he lacked tact a little bit.
00:35:11
Speaker
um Obviously, it's a dialogue, right? So, and there's two main characters and one of them is eventually made to look like an idiot.
00:35:25
Speaker
And it is the side of the church that was defending the geocentric model. And so who that is You know, there's ways to go about things and maybe that was the right thing for him to do. Maybe not. I don't know. That's ah that's that's another discussion altogether. What would you do? I guess is a good question here.
00:35:46
Speaker
You know, you're right. You have the data to back you up. and the other side is just being very recalcitrant what would you do in any case uh so that was one thing that was uh as i mentioned earlier you know just kind of lacking tact there is other aspects of his work though that were very shocking to people I have here a quote from the historian of mathematics and mathematician, I should add, Morris Klein.
00:36:17
Speaker
ah So it's a kind of a long quote, but I like Morris Klein. So I'm going to give you this quote here. Whereas the Aristotelians had talked in terms of qualities such as earthiness, fluidity, rigidity, essences, natural places, natural and violent motion, potentiality, actuality, and purpose,
00:36:44
Speaker
Galileo not only introduced an entirely new set of concepts, but chose concepts which were measurable so that their measures could be related by formulas.
00:36:56
Speaker
me pause here. First of all, We did talk about the Aristotelian worldview and everything was about functions, right? The function of ah Earth is to go to the center and air goes up and whatever.
00:37:11
Speaker
So that gets replaced by Galileo by things that are measurable. I mean, so this is a rapid jump. There was no transition. There wasn't like, oh, well, you know, in between this way of thinking, maybe we can think about it like this. No, he's like, here's this old way of thinking and forget that. Here's a better way of thinking. It was quite aggressive, I guess, intellectually aggressive.
00:37:41
Speaker
Let me continue here with the quote. Some of its concepts, such as distance, time, speed, acceleration, force, mass, and weight, are of course familiar to us and so the choice does not surprise us.
00:37:57
Speaker
But to Galileo's contemporaries, these choices, and in particular their adoption as fundamental concepts, were startling.
00:38:09
Speaker
Yes, indeed, clearly this kind of an abrupt change of systems was disorienting for several of the thinkers of the time. There's kind of a speed limit on, you know, change sometimes, right? It's kind of too sudden for people. You almost kind of have wait generation for the changes to really take hold.
00:38:36
Speaker
In any case, Galileo was uber famous and so his work spread quickly and it was not very friendly at times. And well, you know, wouldn't you know it, the Inquisition, the If you don't know what the Inquisition is, it's the institution of the Roman Catholic Church that just goes ahead and concerns itself with right beliefs, right? You have to believe the correct things.
00:39:10
Speaker
And if you speak contrary to the official doctrine well then you're a blasphemer right so or a heretic even worse so the inquisition condemns galileo to house arrest that was actually not their first choice they wanted to kill him But because he is Galileo, ah people were like, you can't you can't kill Galileo. Sorry. And so they didn't kill him.
00:39:35
Speaker
But he did spend the rest of his life in house arrest. I bet you didn't know that about Mr. Galileo. So...
00:39:47
Speaker
That is terrible. And if you are Descartes seeing all this and you are trying to do the same kind of science and mathematics that Galileo is engaging in engaging in, well then that makes you a little nervous, right? Yeah, it would make me nervous.
00:40:06
Speaker
By the way, if you ever go to Italy, and I think it's in Florence, there is, um you know, a museum. I think it's ah Galileo's old house where you can actually see his middle finger pointed in the direction of the Vatican. I don't know if that's true.
00:40:25
Speaker
I hope it's true. I hope very much it's true. ah But yeah, so very interesting um here that, yeah, I don't know. Go check it out. Okay, so it is a case that Descartes was aware of all this that was going on. He was a a younger man at the time, but he was aware of it.
00:40:49
Speaker
So he wanted to find a way to do science without getting in trouble. Further, let me give you more of a quote here from Maurice Klein. Because he had a critical mind and because he lived at a time when the world outlook, which had dominated Europe for a thousand years was being vigorously challenged, Descartes could not be satisfied with the tenets so forcibly and dogmatically pronounced by his teachers and other leaders.
00:41:20
Speaker
So what Descartes was really realizing here is that it's a problem that people just kind of believe things, uh,
00:41:31
Speaker
not for the right philosophical foundations, not because they had philosophical foundations for them, but just because, you know, the institution, the authorities decided that that's what we have to believe. That's it.
00:41:46
Speaker
So he didn't like that. And we had already mentioned that before. And here's one more element here. Moreover, he felt like all the more justified in his doubts when he realized that he was in one of the most celebrated schools of Europe and that he was not an inferior student.
00:42:08
Speaker
at the end of his studies At the end of his course of study, he concluded that all his education had advanced him only to the point of discovering man's ignorance.
00:42:19
Speaker
So a lot of things contributing to Descartes going and and doing the project that he yeah he did, you know, he wanted to make science safe from religion, right? Reconcile the two.
00:42:34
Speaker
And he was noticing that if you don't do this, if you just dogmatically believe things, that leads to harm. And he was also noticing that he wasn't a dummy and that this was a project that needed to happen.
00:42:50
Speaker
right He felt that humanity was in a state of ignorance. They were still getting mad about, you know you don't believe exactly what I believe. There's got to be a better method and system and way to do things. And that's what he was trying to do.
00:43:09
Speaker
I guess I want to say one more thing here. I don't have a slide for this, but he was not just doing what Galileo was doing. He didn't just want to do science. There's something even further going on with Descartes.
00:43:27
Speaker
Because Galileo was challenging the external authorities of the time, right? For not getting him with the times and looking looking at data.
00:43:39
Speaker
And so that's Galileo's project. But Descartes was doing something else. He was attempting to find a method, a philosophical foundation that could never be silenced.
00:43:54
Speaker
Not by the Inquisition, not by any institution. Because he was trying to find a method by which he can defend reason and rationality and scientific inquiry in the individual's own mind, right?
00:44:15
Speaker
With things that you cannot doubt that you can discover for yourself. So Descartes definitely doing something different here. And all of that will make way more sense by the time that we see what Descartes was working on. So let's move in that direction now.
00:44:35
Speaker
These are Descartes' arguments. As I mentioned, he doesn't go belief by belief, figuring out whether it is a foundational belief or not. He does things in a much more judicious way.
00:44:48
Speaker
And let me begin with his very first argument from his, so he has meditations, plural. This is from the first meditation.
00:45:01
Speaker
It's usually known as the argument from the senses. And here is more or less what Descartes says. In the past, my senses have deceived me.
00:45:13
Speaker
Hence, no sensory information is fully reliable. Remember what I said earlier about your car? If you even once...
00:45:25
Speaker
forgot where you parked it, then the belief of you know where your car is, that cannot serve as a foundational belief. Well, what Descartes is saying here is that your senses have lied to you in the past.
00:45:42
Speaker
Maybe not lied, is that that's actually what he's saying, but lied is maybe too strong of a word, but you've been mistaken. from sensory information. And if you want to look at an example, you know, there's visual illusions, there's auditory hallucinations, whatever, right? Maybe you see someone that you think you know and you wave, but it's not them. And then you pretend that you weren't waving, you were just combing your hair or something, right? You have been wrong when it comes to sensory information in the past.
00:46:15
Speaker
And so what Descartes is saying is that means that sensory information, things that you learn from your eyes and ears and taste and whatever, that cannot be foundational knowledge. It's not the kind of thing that would serve well as a rock solid foundation for the rest of our beliefs.
00:46:38
Speaker
Okay. Typically, when i provide this argument for students, I get a response that's more or less lackluster. And, you know, if I'm going to paraphrase what my students have said in the past, that's too extreme.
00:46:55
Speaker
yeah Our senses are mostly reliable, so we can still trust our senses. Okay, you're not sold yet. Even Descartes wasn't sold yet, so he gives another argument.
00:47:10
Speaker
The argument from dreams.
00:47:16
Speaker
Descartes says something like, in the past, I've been deceived by my dreams. Moreover, there's no reliable way of checking if I'm dreaming.
00:47:28
Speaker
So I can't tell whether or not I'm dreaming right now. Hence again, no sensory information is fully reliable.
00:47:42
Speaker
okay what's going on here? Well, it's definitely the case that we, i think you, just like me, have been deceived by your dreams. I'll give you my own personal examples.
00:47:56
Speaker
I have dreamt all kinds of nonsense. Like it's honestly embarrassing. I can't believe I'm going to share what I'm about to share right now. I've dreamt that, um i don't know, that the sky is water, that i live on a floating island and I look down from it and it's the have dreamt that I'm in an episode of X-Files. I dreamt I was in an episode of I Love Lucy. i don't even like I Love Lucy. I don't know why I had that dream.
00:48:29
Speaker
One time I dreamt I had magneto's powers, meaning I can control metal. And so what I did is I opened up a body shop and people would come in with their, you know, dents in their car and I was just going to yeah zoom and fix it.
00:48:44
Speaker
And so that's what I dream. And during the dream, I'm totally like, oh yeah, I'm Magneto for sure. That's crazy.
00:48:55
Speaker
But that is indeed what I believed at the time. Moreover, there's no way to check that I'm dreaming or not. Now, some people have told me that there is a way to check.
00:49:09
Speaker
And they'll say things like, yeah, yeah, yeah. You just, you know, try to read. you can't read in a dream. But I can. i don't know if you just and don't read enough. I can definitely read in dreams. I can tell the time in dreams.
00:49:22
Speaker
Throw whatever you want at me. I feel like I've done it in a dream. And what that means is that even if your method works once in a while, it isn't foolproof. And again, what are we looking for here?
00:49:40
Speaker
Foolproof foundational beliefs. So yeah, you don't know with 100% certainty, Descartes would say, that you're not dreaming right now.
00:49:53
Speaker
Which leads me to the next point. You have weird dreams if you're dreaming right now. Anyway, so again, Descartes is trying to say, no sensory information is fully reliable.
00:50:11
Speaker
Now, the typical response to this argument is a little more serious. They're like, okay, I'm paying attention now. And people, well, students will even say to me, okay, okay, sensory information may be a little sus. Okay, I'll give you that.
00:50:31
Speaker
But our senses still serve a function, right? They can verify things we know from pure reason, things like mathematical laws. So,
00:50:43
Speaker
This is kind of a ah contrived example I'm going to give you, but you know about the commutative law, right? Of addition, multiplication, that kind of stuff. You know, for example, that two times five is the same as five times two.
00:50:56
Speaker
Cool. I hope you do. This is what you might call a mathematical law or something that you know from pure reason. You just kind of think about it and you say, yeah, that's true.
00:51:07
Speaker
And then what your senses do, like your eyes, is that they help you figure that out, right? They help you verify that. So now with your eyes, you can you know count apples on the screen and you can pair them in two rows of... ah five or five rows of two and it's the same amount of apples. So there you go. Your senses do serve a function here. So maybe this argument is interesting, but there's still to a lot of people something that the senses can do. They can verify what we know from pure reason.
00:51:48
Speaker
Now, I gave you this example because What not everyone knows is that um you can't actually do that in linear algebra. There's actually some versions of mathematics where it's not commutative. Multiplication multiplication is not commutative, actually.
00:52:11
Speaker
And so you can even doubt Descartes is going to say what you think you know from pure reason. So let me give you this argument now.
00:52:22
Speaker
Because Descartes is going big. He's saying, no, I think I can even doubt truths known from pure reason, right? Things like mathematical laws. All right, let's look at his very famous evil demon argument.
00:52:40
Speaker
Here's the first part of it.
The Evil Demon Hypothesis
00:52:43
Speaker
If it is possible that an evil demon developed an artifice to deceive me, then my sensory knowledge and even truths known from pure reason can be doubted.
00:52:58
Speaker
All right, let's just, you know, sit with this for a minute.
00:53:04
Speaker
In the past, whenever you wanted a really powerful entity, ah now we use computers, right? Now we we think, oh, we imagine a supercomputer.
00:53:15
Speaker
But in the past, the best that they can do is evil demons. That's why Descartes is using an evil demon. Although there is another reason, and I'll tell you about that in the next lesson. But imagine a super powerful demon, and imagine, I guess, that you believe in demons too.
00:53:32
Speaker
And they built a big contraption. That's what an artifice means. A big maze, let's just say, just for you. And in this maze, you think you're living you know the real reality, but all of it has been designed to deceive you.
00:53:56
Speaker
My analogy is to a movie that you've probably never watched. It's called The Truman Show. And what the what happens in the movie is that there is a gentleman named Truman, and he is the only person in this, you know, ah very complex reality TV show. He's the only actor, I guess I should say, in this reality TV show.
00:54:25
Speaker
And he lives in a whole community that's been designed just get him to do interesting things so that people can watch him at home. But he doesn't know that it's all make-believe. Everyone except him is an actor.
00:54:43
Speaker
So he you know his best friend is a paid actor. his you All his romances throughout his life were paid actresses, right? So none of it is actually true. Everything that he thought was true, was the case about his life is a lie or in some sense, not quite what he expected.
00:55:07
Speaker
That's kind of the situation with the evil demon. Except even worse, right? You live in some spell where you think that what you're seeing is reality, but maybe you don't have a body.
00:55:24
Speaker
Maybe you're do you do have a body, but it's not at all what you think it looks like. Maybe even math itself, you've been put under that spell so that two plus two, you know you say it equals four, but now it it it doesn't.
00:55:40
Speaker
I mean, stranger things have happened, right? As I mentioned earlier, The law of commutation ah doesn't work in some versions of mathematics. You can't say two times five is the same as five times two in some some other kinds of math. So maybe an evil demon is lying to you about everything.
00:56:05
Speaker
Literally everything. Well, if that's possible, then you can't trust your senses. You can't even trust what you think is mathematical law.
00:56:19
Speaker
The next question, of course, is, is that even possible? Descartes says, well, how do you know it's not possible? Again, he believed in angels and demons and all of the above, right? So for him, it is possible that an evil demon is currently deceiving you.
00:56:40
Speaker
And so you don't have 100% certainty in what you are seeing and what you believe about mathematics. Therefore, Sensory knowledge and even truths known from pure reason can be doubted.
00:56:59
Speaker
Did Descartes just get rid of basically every belief? Maybe. So this is my first pass at this argument, and I hope that persuaded you. That's sort of how Descartes argues for it.
00:57:18
Speaker
A lot of people, though, a lot of students aren't immediately sold on this. And don't worry, we'll do a second pass on this argument.
00:57:29
Speaker
But maybe I'll get a little help from a more contemporary philosopher. Maybe we need to pump our intuitions. So we need a little of a a little bit of technological sophistication.
00:57:43
Speaker
Let's consider this argument again. So this time, let's imagine that rather than an evil demon deceiving us, let's consider the possibility that we are currently in a simulation.