Descartes' Meditations is one of the most important works in modern philosophy (i.e., 17th Century philosophy). It is the point of departure for many philosophical issues and debates up to and including the present. The overall aim of his project is to determine what we can know beyond any possible doubt; that is, what constitutes genuine knowledge. Once we figure out what beliefs are beyond any possible doubt, it is suggested, we can use reason to deduce the rest of what is knowable.
Meditation I is the "destructive" phase of Descartes project. He's going to try to destroy his own confidence in as many of his beliefs as he can. In other words, Descartes is going to show why he can doubt, and therefore reject, just about any of his beliefs. (Spoiler alert: except that he has thoughts and therefore exists).
Philosophical Importance and Context:
One last point before we look at his specific arguments and methods: the context of this whole exercise is important to the philosophical debate between rationalists and empiricists over the source of scientific knowledge. Rationalists believe that true knowledge comes from within; that is, the only beliefs that we can really know are true are those that we access through introspection. Empiricists, on the other hand, argue that if we want to know anything, we have to look at the world: the source of all knowledge comes from empirical observation and experience.
This roots of this debate actually reach back to Plato vs Aristotle and it still rage on today in various incarnations; nevertheless, we're going to pick things up beginning with Descartes.
Although I'll do my best to avoid jargon, there are 2 technical terms that are impossible to avoid in the study of epistemology and most philosophy, so we might as well get them out of the way right now:
A priori: This means "before experience." It refers to the category of beliefs we can have without having to go out into the world to verify their truth. For example, you don't need to go running around with a measuring stick to know that the shortest distance between any two points is a straight line.
Similarly, if you know that the interior angles of a triangle = 180 degrees, then, given either only 2 interior angles or an interior angle and the length of the adjacent side, you can infer the other 2 angles. You don't have to go measure each triangle to verify. We can know the angles will be right before we measure.
Definitional truths also fall into this category, like "all bachelors are unmarried men." We can know this before empirical experience. All we need is an understanding of the two concepts "bachelors" and "unmarried men." You don't need to go around interviewing bachelors to find out if they are also unmarried.
A posteriori: This means "after experience." A posteriori knowledge refers to beliefs that we can only know as true once we have gone out into the world and verified them. For example, "apples are red" or "Miley Cyrus danced with giant teddy bears." Before we can know whether these beliefs about the world are true or not, we'll need some sort of empirical evidence.
Part 1: Explanation of Method. Method of Doubt
In the first part of the 1st Meditation, Descartes takes a moment to explain what he's about to do. He says something along the lines of:
Have you ever had the experience where you realize that something you thought was true as a child turned out to be false? Or maybe it was only a few years ago that you thought Santa was real...
The point being, few of us ever stick with the exact same set of beliefs for the entire duration of our lives. Sometimes our experiences teach us that a previously held belief was false. So, why should we suppose that at this particular point in our lives, all of our beliefs are true? I mean, seriously, given all the different conflicting beliefs in the world about the 1000s of different possible topics, what are the chances that YOU, at this particular moment in time, just happen to have stumbled upon all of the true ones and EVERYBODY ELSE, except you, has some false beliefs? Take a moment to do the calculation if you like...
So, here's the problem. Supposing that some of my current beliefs are false, how am I to distinguish them from the true ones if I know that some that I previously believe to be true turned out to be false (Curse you Santa!). How do we tell in advance which beliefs are true and which are false?
His solution to this problem is to treat any belief that has even the remotest possibility of being false, as false. That is, he will not only reject beliefs that can be shown to be false, but also beliefs that could be false--even though maybe he can't show them to be false.
The net result will be that whatever beliefs cannot possibly be false will necessarily be true. Once he establishes all the necessarily true beliefs (the ones that withstood all doubt), he can deduce the rest of his knowledge. In other words, since many beliefs rest on a foundation of prior more fundamental beliefs, if we can establish a firm foundation, then we can construct a strong edifice of knowledge.
Let's formalize the method:
Suppose we want to know if something (P) is true.
(P1) The only way I can know for sure that P is true is if I cannot possibly doubt its truth.
(P2) But I can doubt P is true.
(C) Therefore, I do not know that P.
('P', in philosophy, usually stands for "some proposition" kind of like how 'x' is used in math to represent "some number")
Now, lets go back and look a little bit more at that previous idea--the edifice of knowledge built on a firm foundation. Descartes' idea of the "structure" of knowledge is what's known as foundationalism. Foundationalism is the theory that all beliefs (or knowledge) ultimately depend on other more basic beliefs, which in turn depend on more basic beliefs, and so on until you get to the beliefs that are foundation of all your beliefs. In short, the structure of knowledge is heirachical.
Because of the "shape" of knowledge in Descartes' foundationalism, you can deduce or infer higher level beliefs from the more basic beliefs...kind of like doing geometry or arithmetic. (This is no coincidence since Descartes was primarily a mathematician and geometer. If I know from the rules of arithmetic that 1+1=2, then I can infer that 2+1=3 and so on. I can infer from my basic knowledge of the rules new knowledge that I didn't have previously.
So, why were we talking about foundationalism anyway? Oh right...because instead of Descartes' piecemeal going through every single one of his beliefs and subjecting them each to doubt (is this really a chair I'm sitting on? Is it really black? Did Miley Cyrus really just do that?) he can shorten the process by only looking at the foundational beliefs. If the foundational beliefs are subject to doubt then everything else that's built on them will also come a tumblin' down.
The Argument from the Unreliability of the Senses:
Sometimes when I see a tower from a distance, it looks rectangular, but when I ride my horse up close to it, the tower is in fact round! Or sometimes when I'm walking my dogs at night, I think I see another dog in the distance, but in fact it's just a garbage can.
Given that my senses can fool me, why should I put any stock in my sensorily acquired beliefs? As a famous man once said
But, Descartes realizes that if he were to fully commit to this argument, his position would be no different from that of a raving madman--it's a bit too crazy. Sure, we can all agree that sometimes under certain conditions our senses fool us about the external world, but it's a bit of a stretch to move from that to the idea that we can't trust anything our senses tell us.
Lets quickly formalize the argument:
(P1): Sometimes my senses fool me.
(P2): I can't distinguish between when they are fooling me and when they aren't.
(C1): Given (P1) and (P2), I can't confidently say that my sensorily acquired beliefs are true.
Counter argument: Simply because my senses sometimes deceive me about the external world, it doesn't necessarily follow that I should reject all sensorily derived beliefs. Maybe the one's that are most obvious, like "I have a body" or "the chair I'm sitting on is solid," are more probably true than untrue.
So, where are a priori beliefs in all this? So far, the argument from the unreliability of the senses leaves them untouched. The ability for our senses to fool us about the external world has no effect on the truth of "all bachelors are unmarried men" or "the shortest distance between 2 points is a straight line." I don't need the outside world to know that these assertions are true--all I need is an understanding of the relevant concepts.
The Dream Argument (Argument vs Empirically-Acquired Beliefs)
Sometimes when I'm dreaming I imagine I'm flying but I'm actually lying in my bed. Or maybe I dream that my arm is cut off or that I'm late for class, but that's not what's actually happening. Surely, we can all agree that we've been fooled by dreams that seemed real at the time we were dreaming.
This raises a problem: How do can we distinguish between when we're dreaming and when we're awake? How do I know whether I'm a butterfly dreaming he's a human or a human dreaming he's a butterfly? Because I can sometimes fail to make this distinction, it follows that I can't be sure that my beliefs about the external world are entirely free from any doubt.
Lets formalize the argument:
(P1) When we are dreaming, we cannot always distinguish whether we are dreaming or whether we are awake.
(P2) It follows from P1 that there will be times when we think we are awake and form beliefs about the world but in fact we aren't awake, and so those beliefs are actually false.
(C) Therefore, it is possible to doubt the truth of our beliefs about the external world.
Descartes brings up a possible counter argument: Lets suppose I am dreaming and in my dream I have purple octopus arms and the head of a dragon. Surely, this does not match up to the world as it is. However, all the perceptions of the basic constituent parts of my dream, like the color purple, the shapes, the textures, size, quantity, temporal duration and so on, all had to have come from somewhere. As he says:
[...] it surely must be admitted that the things seen during slumber are, as it were, like painted images, which could only have been produced in the likeness of true things, and that therefore at least these general things--eyes, head, hands, and the whole body--are not imaginary things, but are true and exist.
In short, you cannot imagine things ex nihilo (out of nothing); the original building blocks of your ideas have to originate from somewhere besides the inside of your head.
What follows from this? Here Descartes argues that because we are able to mix and match general and universal qualities in any manner of ways in our dreams and imagination (and sometimes we can't tell when we're dreaming) we must doubt truths that are about composite ideas. That is, ideas about things other than the fundamental properties of our thoughts. Some examples of things about which we can doubt are physics, astronomy, medicine (because they are about composite things).
So, what types of beliefs does the dream argument leave untouched? The answer is beliefs about disciplines that trade in a priori beliefs; that is beliefs about things we don't have to go out in the world to verify for truth. Arithmetic, geometry, for example, don't require for us to go out into the world to verify the truth of their assertions.
For example, when I divide 100 by 25 and give the answer of 4, I don't need to go out and physically manipulate things into piles to verify this truth. So long as I correctly follow the rules of arithmetic, I'll have the right answer. Not only will I have the right answer, but I'll have the right answer whether I'm dreaming or not. That is, regardless of whether I'm dreaming, so long as I follow the rules of arithmetic, I'll have the correct answer.
The same applies for geometric proofs. A square will have 4 sides whether I'm dreaming or not. If it doesn't, then it's no longer a square--it's something else. The same also applies to the bachelor example...and all a priori knowledge.
In the next section there's a little digression where Descartes talks about the possibility that his creator, if he so chose, would be able to be deceive him even about algebraic and geometric facts (i.e., a priori beliefs). Then he remarks that the combination of the 2 arguments and the possibility the God could deceive him are not quite enough to break him of his habit of trusting his sensorily-derived and a priori beliefs. He finds himself slipping back into the habit of assenting to them because it's "much more consistent with reason to believe them than to deny them." The same applies to God as a willful deceiver.
To prevent himself from slipping back into his old ways and to help him stick to his project of trying to reject any belief that it is possible to doubt, he's going to need a stronger method.
Enter the demon argument...(cue ominous music)
The Demon Argument (Or the Matrix)
Here we are to imagine a powerful evil genius who has dedicated himself to deceiving us. Everything you experience has been constructed by the evil genius. Here's the modern equivalent of the argument
The idea is this: All of your thoughts are being fed to you by an evil genius or a computer program--take your pick. Supposing this scenario, what can we know, that is, what beliefs can we have that we can be 100% sure are true?
If you've read the 2nd meditation, then you know...