Rene Descartes - What Can Be Doubted and What Cannot (Discourse, pt. 4) - Philosophy Core Concepts

Hi, this is Dr. Gregory Sadler. I'm a professor of philosophy and the president and founder of an educational consulting company called Reason.io, where we put philosophy into practice. I've studied and taught philosophy for over 20 years, and I find that many people run into difficulties reading classic philosophical texts. Sometimes it's the way things are said or how the text is structured, but the concepts themselves are not always that complicated, and that's where I come in. To help students and lifelong learners, I've been producing longer lecture videos and posting them to YouTube. Many viewers say they find them useful. What you're currently watching is part of a new series of shorter videos, each of them focused on one core concept from an important philosophical text. I hope you find it useful as well. Perhaps the idea that René Descartes is best known for is what you see here. I think, therefore I am, expressed in French, je pense, donc je suis, and expressed in his Latin cogito ergo sum. How does he get to that? Well, he goes through a process of methodological doubt, which is summarized in the beginning of part four of his discourse on method. Whether we look at this work or we look at the longer meditations, we see that there's a kind of progression that Descartes is going to follow. He thinks that it's very important that we clear away our previous sets of beliefs, and that's what methodological doubt is designed to do. He doesn't use the term methodological here, but that is something that it's come to be called. What does he do? He says, I'm going to reject everything that is dubitable, everything that I can possibly doubt. He says, I'm not going to do this with morals, that we've already talked about that in the provisional morality, but he says, I wanted to concentrate on the pursuit of truth, so I decided to reject as completely false everything in which I could detect the least doubt. So he's not going to go by probability. He's not going to say, well, generally for the most part, things have turned out this way, so I can rely upon it. He's saying for once in my life, I am going to engage in this rigorous scorched earth policy of getting rid of everything, anything that can't stand up to complete scrutiny, anything where there could be an exception, anything where I could potentially be wrong. As it turns out, that's going to cover quite a lot. He begins by talking about our senses, sight, hearing, taste. These do sometimes deceive us. Whether it be in sight, you know, he likes the example of looking at a square tower and it looking round in the distance, or, you know, they always love the example of putting a stick in water and seeing it appear to be bent, even though it's not really bent. You might think of the illusion that's taking place right now as you are watching me in a previous moment, one that's now long past me talking to you about Rene Descartes, right? That's involving sight and hearing, and the same thing happens with our senses of taste or touch. As a matter of fact, we live in a time in which because of technology, we have found more and more ways to deceive ourselves about this. You know, think about food that's not actually wholesome, that we can make taste in certain ways, right? So what is the upshot of this? He says, all right, anything that I've received through the senses, I'm going to assume that nothing is the way that the senses represent things to be. Now that's more than just saying, I'm going to assume things to be the opposite. So I'm going to assume this thing that I'm tasting to be salty, to be sweet instead. He's saying, I don't even know if I'm tasting something. I don't know what taste is. I'm not going to make assumptions that any of that has to do with anything real whatsoever. I'm going to suspend a scent or suspend belief when it comes to everything that comes through the senses. That's going to cover a lot as we're going to see. What else? Can we go further with doubt? Descartes, and this is where it becomes very, very radical because skeptics had already, you know, suggested in many times that the senses are deceiving, but maybe we could have something just in our mind or in communication or argumentation that would get us beyond that. So he says, there are some who make mistakes in reasoning, even about the simplest elements of geometry. Geometry begins from axioms and then it proceeds outward through this essentially mathematical reasoning or if you like, logical reasoning, and everybody should be able to grasp it. And yet we see people making not just dumb mistakes through carelessness, but we see people who genuinely don't get it sometimes. He also talks about people committing logical fallacies, not people just trying to deceive others, you know, by using logical fallacies, they fall into those fallacies themselves, making ad hominem attacks, you know, the fallacies that have to do with parts and holes like composition and division. We could go on and on and on, right? And he says, I'm not claiming that I'm perfect in this respect. I have made mistakes myself. So what does that mean then? We have to reject all previous reasoning and what we think to be proofs, including not just the things that have to do with, you know, the world of sense, like physics or, uh, you know, maybe even like, you know, very practical applications in terms of mechanics or cooking or something like that. We have to also reject logic and geometry and mathematics, at least for the moment. He'll bring those back in very quickly enough, but can we call that into question? Now you notice that's a much deeper level of doubt than just saying, well, sometimes the senses deceive us. So I don't know what I'm getting through the senses. He brings up a third thing, and this might seem redundant to some of you, but it actually does serve a very important purpose in closing off possibilities. He points out that we can have the same thoughts in our mind when we're awake as when we are dreaming. He says they can come to us while asleep without any of them being true. So he said, I resolved to pretend everything that had ever entered my mind was no more true than the illusions of my dreams. And you can say, well, that's probably, you know, covered under our senses deceiving us or making mistakes in reasoning. Right? I mean, those are things that entered into our head, but what if we had something that entered into our head and it didn't come through the senses, but it was, you know, things that we could say are sensual, they look like it. What if somebody implanted something in our mind, whether it be through technology or magic or, you know, some sort of supernatural divine illumination, this would eliminate that as well. Now we see that Descartes has really stripped away so much that we could rely upon. One of the things that he doesn't talk about here that we might also want to bring into consideration is anything that somebody else has told us, whether we learned it in a book or we took a class or we talked about it with them, or it actually was something that we worked out together in conversation because our senses could be deceived about what the person actually said. Or if we were following out lines of reasoning, maybe they were actually on track and we got it wrong somehow, you know, how do we know that every time that we add two and two it's not actually five and we're just getting four and we happen to be the only person who screwed up about that, but everybody treats us differently. We could come up with all sorts of interesting ideas about that. Descartes doesn't do that here because he's done that in other places. But notice that this hyperbolic or methodological doubt, it has rejected an awful lot, not only of our experiences, but even of our thoughts. Does that mean that we can doubt everything? Here's where we arrive at what Descartes is going to refer to as his Archimedean point, the beginning point that he can use in philosophy. Archimedes had said, just give me a fixed point and a lever long enough and I can move the entire world. Descartes is saying that about the world of thought. So he says immediately afterwards, I noted that while I was trying to think of all things being false in this way, there was one thing I couldn't think of as false. I, I exist. Why? Well, there has to be somebody, something there that's actually doing the doubting. Even if I'm deceived, Augustine had said this, Descartes says this as well, even if I'm deceived, I still exist in order to be deceived. So he says, it was necessarily the case that I, who was thinking these thoughts had to be something and observing this truth. I am thinking, or I think, therefore I exist in French, je pense, donc je suis in Latin in the meditations, cogito ergo sum. This is often called the Cartesian cogito. That is something that methodological doubt cannot erode or efface. That is one of the limits of methodological doubt. That is something that cannot be doubted. Why not? I mean, you can say, but I'm doubting it right now. Oh, are you? You're doubting it. You exist, don't you? Now there, there, there have been some interesting objections to this, but all of them are really subject to that sort of retort who's doing the doubting what's doing the doubting who's talking right in that conversation. What does this give Descartes? He says, I could pretend that I had no body and that there was no world. Those are things of the senses, right? So we don't have to say that everything comes back in because of cogito ergo sum, but we can say I had no body. Maybe there's no world, no place for me to be in, but I cannot pretend that I do not exist. Why? He says it's so secure, so certain it cannot be shaken by any of the most extravagant suppositions of the skeptics. It is clear and distinct. You can say to use Descartes criteria. So he says, um, I concluded therefore that I was a substance or, uh, a thing whose whole essence or nature resides only in thinking and which in order to exist has no need of place and is not dependent on any material thing. Now that is more than just the statement. I think therefore I exist, but it's coming out of it and Descartes likewise thinks that ultimately my being and your being a thinking substance is not something that can be genuinely doubted. We can certainly say the sentence. I doubt that that's the case or other people say different things, but if you follow Descartes line of reasoning, then it really is something that can't be doubted. There is an issue that I'll bring up in conclusion. Should we say that perhaps we could make mistakes in reasoning about this? Descartes thinks that we don't. Descartes thinks that we cannot, and therefore we can't actually doubt that. I think therefore I exist, nor can we doubt that we are substances that are thinking and whose essence and nature consists in thinking. So that shows us where the limits do in fact lie.