G.E. Moore A Refutation of Skepticism The Argument For Skepticism 1. If you do not know that you are not merely a brain in a vat, then you do not even know that you have hands. 2. You do not know that you are not merely a brain in a vat. 3. Therefore, you do not know that you have hands (nor, in fact, ANYTHING about the things in the world around you; the objects of your experiences). The argument above has a certain form it is called a conditional argument. And conditional arguments have TWO valid forms. Consider: Argument #1: 1. If someone is old enough to drive, then they are at least 16 years old. 2. Frank is old enough to drive. 3. Therefore, Frank is at least 16 years old. Argument #2: 1. If someone is old enough to drive, then they are at least 16 years old. 2. Frank is NOT at least 16 years old (rather, he is only 12). 3. Therefore, Frank is NOT old enough to drive. Notice that both of these arguments are good ones. The conclusion MUST follow from the premises. They have the following format: Argument #1 (modus ponens) Argument #2 (modus tollens) 1. If P, then Q 1. If P, then Q 2. P 2. Not Q 3. Therefore, Q 3. Therefore, not P Both arguments have exactly the SAME first premise. Only premise 2 differs. But, both arguments cannot be right. Only one of them can be. Philosopher G.E. Moore noticed this, and suggested that, while the argument for SKEPTICISM takes the form of Argument #1 (modus ponens), ANOTHER argument can be offered which takes the form of Argument #2 (modus tollens). Namely, this one: 1. If you do not know that you are not merely a brain in a vat, then you do not even know that you have hands. 2. You DO know that you have hands. 3. Therefore, you DO know that you are not merely a brain in a vat.
So, we have two competing arguments but only ONE of them can be right. But, the only difference in the premises of the two arguments is premise 2 (for, their first premise is exactly the same). So, we must decide between these two claims: 2. You do not know that you are not merely a brain in a vat. OR 2. You DO know that you have hands. Moore argues that, whenever we are trying to decide between two conflicting premises, we should go with the more plausible one. But, it is FAR more plausible that I do have hands than it is that I am merely a brain in a vat. So, we ought to accept the second argument rather than the first. This strategy is a common one and is actually known as The G.E. Moore Shift. Notice that, unlike Descartes, the emphasis here is not placed on CERTAINTY. If we demanded absolute CERTAINTY for knowledge, then we would know very little. And this seems to be more in line with how we use the word knowledge in everyday language. For instance, if someone asked, Do you know that there is a desk in front of you? you would respond, Yes, of course! But, then, if they came back and asked, Do you REALLY KNOW that there is a desk here? You might be dreaming. Or hallucinating. You might respond, Well, I can t KNOW FOR SURE that there is a desk here, but I have a pretty good idea that there is one. Here, knowledge is being used in two different ways. We MIGHT insist that knowledge requires ABSOLUTE 100% CERTAINTY. But, that seems too strict. Rather, it seems that knowledge refers to something like All evidence points in this direction, so my best estimate is that there IS a table here. Moore says that Skeptics are confused, thinking that, in order to KNOW something, one needs to be able to PROVE it. Moore claims that he KNOWS that here is a hand is true, though he can t PROVE it (because he can t prove that he is not dreaming, for instance). But, Moore notes, there are LOTS of things that we know without being able to prove them. For instance, I know that I spilled some coffee yesterday, that Hydrogen has one proton, and that I have two hands though I cannot prove any of these things. People CONSTANTLY take the sort of argument he has just provided as the only sort that is ever needed in order to establish some conclusion. For instance, imagine that you and your friend disagree about whether or not there is milk in the refrigerator. In order to settle the dispute, all that you need to do is open the refrigerator. Here is some milk in the refrigerator, you say, while pointing to the milk. Therefore, there is milk in the refrigerator. What more could possibly be needed?
Chalmers Against Skepticism Philosopher David Chalmers has a solution to the problem of external world skepticism. The short version: You can know that you have hands even if you ARE a brain in a vat! 1. The Matrix as Metaphysics: Imagine that you are living 1,000 years ago. You look at some water and form the belief, <This is water>. Do you KNOW this? Plausibly, yes. Now, centuries later, scientists will discover that this substance is composed of H2O. You didn t know that you were looking at some H2O, but does it matter? No. It just doesn t seem like ignorance about the underlying, fundamental structure or nature of something undermines this sort of knowledge. In fact, you might have even held MISTAKEN beliefs about the underlying structure for instance, you might have said that water is composed of tiny corpuscles that are perfectly round (that s what makes it so fluid!). But, being mistaken about this fact doesn t undermine your knowledge that <This is water>. Right? Well, Chalmers says something similar about the simulation scenarios. Imagine that you ARE a brain in a vat. You look at your digitally-rendered hands and form the belief, <I have hands>. It is very tempting to think that you lack knowledge in this case. Your belief is simply mistaken. You do not have hands. But, Chalmers argues that, even if you are a brain in a vat, you DO have hands. If you look down, and see and feel hands, then you have them! They might be composed of earth/air/fire/water, or atoms, or superstrings, or zeroes and ones. Ultimately, that doesn t matter. You don t need to know anything about their underlying fundamental structure in order to know that you have them just like you don t need to know anything about H2O in order to know that water exists. So, ultimately, the Matrix Hypothesis is not a skeptical hypothesis, but rather a metaphysical one about reality, its fundamental structure, and our relation to it. 2. Three Non-Skeptical Hypotheses: Chalmers notes that his proposal is really just the combination of three hypotheses, none of which are skeptical: The Creation Hypothesis: There exists some creator of our reality which is in some sense outside of this reality. This is not a skeptical hypothesis. It is much like the belief in God, and we would not say that theists are external-world skeptics. Alternatively, many physicists speculate that our entire universe is just one among many, or that ours is entirely inside of some black hole that exists in the next universe up.
The Computational Hypothesis: Reality, at its most fundamental level, is ultimately composed of bits (of information; i.e., zeroes and ones). This is not a skeptical hypothesis. There are many competing views about the fundamental structure of reality, and the leading view is equally bizarre. Physicists tell us that everything is ultimately composed of vibrating strings whatever those are; and that seemingly solid objects like tables and trees are really mostly empty space, not solid at all! If this is not a skeptical hypothesis, then neither is Chalmers hypothesis. The Mind-Body Hypothesis: Our minds are located outside of this reality that is, outside of this space-time continuum but interact with things in this space-time. Consider: If I am a brain in a vat, then my brain is elsewhere, unobservable, imperceivable, and not a part of this reality. And yet, it interacts with this reality by having conscious experiences. This is not a skeptical hypothesis either. Most of the people who have ever existed have held this view. For, it is much like the view that our mind is located in an immaterial soul. Much like God, souls are typically thought to be outside of space-time, yet interact with it. (more on this later in the course) Conclusion: If none of its components result in skepticism about the external world, then the combination doesn t either. So, even if we ARE brains in vats, we should not endorse skepticism about the external world! 3. Objections: Most readers will probably still have these lingering worries: (a) It seems like the following are all FALSE when uttered by a brain in a vat: I am outside in the sun I am in Tucson I have hair Reply: Chalmers believes that our terms refer to whatever it is that we re referring to when we point to them. If I look in a mirror and see hair, then my term hair refers to THAT stuff, whatever it is. If I visit Tucson, then my term Tucson refers to THAT place, whatever it is. It just turns out that someone living in a simulation has terms that refer to what we might call virtual hair or virtual Tucson and so on. Sure, if we are looking in from OUTSIDE a simulation at some beings who are INSIDE of one, they will seem mistaken. For then, OUR term hair would refer to physical hair rather than virtual hair. But, that is only because OUR terms would refer differently than theirs. Simply put: In a physical world, real hands are made of atoms (or strings, or whatever). In a simulation, real hands are made of bits.
(b) How about this one? I have friends Reply: It is possible that you have friends, even if you are in a simulation. If either (a) there are other envatted brains in the simulation along with you, or (b) your friends are purely computational, but nevertheless conscious artificial intelligences, then your friends are real. Now, we can t be SURE of this, but this is just the problem of other minds, which is a problem even for beings who are NOT in simulations. (c) But, to believe in the external world is to believe in physical objects, not virtual objects. Simulation is not reality! So, if I believe that there are real things, and I turn out to be in a simulation, then I am wrong about almost everything! Reply: Once again, Chalmers believes that you are NOT mistaken about most things. Hands and hair and tables and trees are all REAL in a simulation. Only, their fundamental structure is different than most people think. So, if you believe some abstract proposition like, <The fundamental structure of reality is superstrings>, you ll be wrong, but if you believe something ordinary like, <I have hands>, you ll still be right. Now, if you insist something like, By terms like hands, I am referring to physical objects that are definitely NOT composed of computational bits of information, and you are in a simulation, then I suppose it turns out that you are wrong about a lot of things. But, do we really have pre-suppositions about the fundamental nature of reality built into our ordinary terms for physical objects? If so, then, when Plato believed he was drinking water, he was wrong (because he had built a mistaken assumption about its fundamental nature into the term). But, that seems odd, right? 4. Conclusion: Chalmers puts it this way: I suggested before that it is not out of the question that we really are in a matrix. One might have thought that this is a worrying conclusion. But if I am right, it is not nearly as worrying as one might have thought. Even if we are in such a matrix, our world is no less real than we thought it was. It just has a surprising fundamental nature. (5) [For a great synopsis of the problem of external world skepticism, as well as some replies, you might watch these videos by philosopher Jennifer Nagel, The Problem of Skepticism, Three Responses to Skepticism (includes Moore s response @ 6:25), and New Responses to Skepticism (includes Chalmers response @ 6:34).]