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Descartes’ Method of Doubt
Philosophy 100 Lecture 9
PUTTING IT TOGETHER. Descartes’ Idea
- The New Science. What science is about is describing the nature and interaction of the ultimate constituents of reality.
- The Thesis of Rationalism. We come into the world with, in some sense, knowledge of the most basic principles of physics—of the notion of a cause, of the understanding that matter must take up space, that one things cannot be in two different places at one, etc.
- The New Algebra. We have a way of describing the geometric properties of these ultimate constituents of reality.
- Mathematical Proof. By using the rules of logic, and axioms of physics (given to us innately by God), we can construct mathematical proofs about the nature of physical reality.
I. The Requirements of Certainty. What are the requirements for a system which is certain, which yields results or conclusions that are certain to be true? Two Conditions.
- Each of the initial premises must be indubitable (no one could doubt it) and incorrigible (not subject to correction). In other words, each premise must be such that were any person — any minimally rational and sane person — to consider that proposition, he or she would agree that the premise is true.
- Each step of the argument must follow indubitably from the previous premise(s). In Descartes’ terms, we can simply see by The Light of Reason, that each step must be true given the previous step(s). These two requirements are separate and distinct. (1) concerns the truth of the premises ; (2) concerns the form of the argument. Descartes project requires that both of conditions be fulfilled.
Back to Descartes’ Project… Descartes begins the First Meditation by looking for the first premises (or axioms) for his theory of knowledge. He is going to examine his present beliefs, not one by one, but type by type. His method is to select only those types of beliefs that he can declare to be true without any doubt. I. Doubt about “Unclear Perceptual Beliefs” There are many perceptions we have that we know are untrustworthy. E.g. If you’ve forgotten your glasses, or are trying to identify something in the far distance, or know yourself to be drunk, etc.such perceptions are clearly untrustworthy.
II. Doubt about each perceptual belief. Descartes asks: Is there any general reason to doubt each and every one of my standard perceptual beliefs (barring the one answer that I am insane)? That is, is it certain that, for example, that you are sitting in a large lecture theatre, in the Images Theatre, listening to a philosophy lecture on Descartes? Is there any room for doubt here at all — any reason to think that, maybe , it might not be true? Descartes’ Answer: It is possible that at this very instant, you are dreaming — e.g. you are actually at home in bed, tossing and turning, in the midst of a truly horrible nightmare , namely the nightmare that you are in an introductory class at Simon Fraser University, listening to a lecture on Rene Descartes’ Method of Doubt and you have not done the assigned readings !! THIS IS POSSIBLE. And if this is possible that right now you are dreaming, then it is possible that for each and every perceptual belief that you consider, the ones you are having right now , that each one is false as well.
Reply : Yes, but when you have the dream, strangely, you do not notice these inconsistencies — we all have dreams in which people change identities, look nothing like they should, or appear in places they could not possibly be. The Standard Counter-Objection. Alright, perhaps I can’t verify that my perceptions, right now, are not the product of a dream. But if I wait awhile, either I will wake up or I will not. Thus, after I have the sensation of waking up, I will know that what I was perceiving was a dream but what I am now perceiving is veridical (true). The Counter-Reply. Suppose we admit that you are sometimes awake and sometimes asleep, that we set aside the possibility that you are always dreaming. The question is this: how could you verify that you are awake NOW? How do you know that your present perceptions are veridical? —You may seem to wake up, but this too may be a dream. —If you are asleep, you will not notice any inconsistencies that are now present; so you can’t count on the fact that, now , there do not seem to be any inconsistencies.
Thus there is no way to tell whether you are asleep now. Thus there is no way to tell whether you are asleep now. BUT, BUT, BUT…Is Descartes saying that we could be dreaming all the time? Does this really make any sense to think that we could be dreaming all the time? Because if we were dreaming all the time, what would be the difference between waking and dreaming.
All Descartes needs to prove is that for each perceptual belief, as I consider it , that belief could be false. III. Doubt about the “commonalities” of my perceptions. Even if we are dreaming now, and the world does not exist exactly as we now represent it, don’t we still know some general truths about it? Don’t I still know what my own apartment looks like, where I live? Or if I can’t be certain of that, don’t I still know that there are objects, like cats and dogs and buildings and bridges? And don’t I still know that there are, in general, objects that exist through space and time, are extended, etc. Even if I were dreaming, wouldn’t 2 + 2 = 4? Could I possibly be deceived about these things?
Descartes’ Answer: The Evil Genius It is possible that, unbeknownst to you, there is an evil demon, who controls your sensory perceptions, all that you see, hear, feel, smell, etc. Not only do you not have a body, not only are you wrong about all of the events that seem to happen, but perhaps there is no external world at all or a world that has properties we can not even begin to imagine. A Modern Example: The Brain in the Vat. Suppose that, unbeknownst to you, your brain has been put into a nice vat of saline solution, its arteries are given a nice supply of artificial blood, and its sensory neurons are hooked up to electrical devices that stimulate the nerves in ways that will produce, in your brain, sensory perceptions of certain kind — whatever kind your abductors want you to have. On the output side, there are sensors that read the signals of your out-going nerves, signals that are translated into the kinds of effects you would have brought about if you still had a body — e.g. scratching your left ear. You are, in effect, you are the virtual pet of an alien species. Your entire world is merely virtual. If this were true, nothing you now believe about the external world need be true—the world could be entirely different from what you now believe.
So what, if anything, would be left? Is there anything you can say you know? Yes. There is. Insofar as I am thinking or think that I am sitting in a lecture theatre, then I know that that is what I am thinking. It seems to me that I am sitting in the lecture theatre. I may not be in a lecture theatre, I may not be sitting, but that doesn’t matter. Because no matter whether there is an evil genius or whether I am a brain in vat or whether I am dreaming at the moment, I know how things seem. This is how Descartes arrives at The Cogito: I think, therefore I am. Insofar as I am thinking, I exist. Insofar as I think that I am sitting in a lecture theatre, it is true that it seems to me as it I am sitting in a lecture theatre.
Question for Tutorial: Do you think it is possible for people to make a mistake about what they are thinking at the present—about the contents of their own thoughts? If you agree with Descartes’ argument so far, then what Descartes has proved is that there are very very few things that we know—very few facts for which we have indefeasible evidence.
