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G.E. Moore – A Refutation of

1. The Skeptic’s Challenge: Recall the experiment of someone who is merely a experiencing life inside of a computer simulation. Imagine the brain thinks to itself, “I have hands.” This is FALSE. This person does NOT have hands. They’re merely a brain with no body! And the same goes for most of this brain’s beliefs. In the simulation, it may think to itself, “I go to W&M”, “I saw Professor Vance this morning”, “I am eating pizza”, and so on, and ALL of these beliefs would be false. In short, brains in vats have a knowledge problem—they THINK they know lots of things, but they don’t (after all, you can’t know something that is false!). They’re systematically deceived.

Now, we’ve said that no one can rule out with CERTAINTY the possibility that s/he is a brain in a vat. It’s at least POSSIBLE, however unlikely. Well, the skeptic thinks that the mere POSSIBILITY that you are a BIV undermines your ability to know things even if it turns out that you are living in world and are NOT a BIV.

Why? Consider a court case. You can’t be justified in convicting Sally for the murder if you haven’t ruled out Marie as a suspect. Right? The skeptic says something similar: You can’t be justified in believing that you’re in the REAL world (and have REAL hands, and eat REAL pizza, etc.) if you haven’t ruled out the possibility that you’re a BIV.

2. The Moorean Shift: G.E. Moore offers the following argument against skepticism:

Here is one hand. Here is another. Therefore, external world skepticism is false.

The End. Moore concludes that “nothing is easier than to prove the of external objects.” Uh… What? What just happened? Let’s take a closer look.

Recall that the argument for skepticism was as follows:

The Argument For Skepticism 1. If you cannot know that you are not merely a brain in a vat, then you do not know that you have hands. 2. You cannot 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 ).

The argument above has a certain form – it is called a “conditional argument”. And conditional arguments have TWO valid forms. Consider:

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Argument #1: 1. If someone is old enough to legally drink alcohol, then they are 21 or older. 2. Frank is old enough to legally drink alcohol. 3. Therefore, Frank is 21 or older.

Argument #2: 1. If someone is old enough to legally drink alcohol, then they are 21 or older. 2. Frank is NOT 21 or older (rather, he is only 12). 3. Therefore, Frank is NOT old enough to legally drink alcohol.

Notice that BOTH of these arguments are ones. In EACH of them, the conclusion MUST follow from the premises. They have the following forms:

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 sound. 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 cannot know that you are not merely a brain in a vat, then you do not know that you have hands. 2. You DO know that you have hands. 3. Therefore, you CAN (and now 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 cannot know that you are not merely a brain in a vat. OR 2. You DO know that you have hands.

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Moore argues that, whenever we are trying to decide between two conflicting premises, we should accept whichever is more plausible. But, it is FAR more plausible that I do have hands than it is that I do not know that I am not merely a brain in a vat. The former is a belief, while the latter is a philosophical thesis (the result of the following reasoning: You only perceive sense-data, and, in order to know that you aren’t a BIV, you’d have to be able to confirm that your sense-data accurately represent )— and surely common sense beliefs are always more plausible than philosophical theses. So, we ought to accept the second argument rather than the first. Huemer writes,

“a common sense belief could not be refuted by another, non-common-sense belief; the effect of a conflict between two such beliefs would be that the non- common-sense belief would be refuted instead.” (SVP, 35)

This strategy is a common one and is actually known as “The G.E. Moore Shift.”

3. Objection: Return to the court case example. You’re on the jury. You’re pretty sure Sally is the murderer. But, then, another juror asks you, “But, have you ruled out the possibility that MARIE did it!?” Would the following reply be rational?

“No. But, the possibility that Marie is the killer conflicts with my belief that Sally is the killer, which I’m quite confident in. So, I must decide between them. And my stronger confidence in the latter entails that the former is false.”

It would be absurd to reply in this way. You’re appealing to your “knowledge” that Sally did it in order to demonstrate that this verdict is conclusive, and that any evidence to the contrary is mistaken. But that’s circular reasoning.

…Isn’t G.E. Moore just doing the same thing?

Reply: Huemer points out that, first, we have to recognize that sometimes, some of the beliefs that we already have DO justify the rejection of other evidence to the contrary.

For instance, imagine that you are calculating the circumference of the Earth for your science class, and you get the result: 32 miles. You have used the formula that you copied down in class, and you’ve double-checked your work several . Everything seems fine. What would your reaction be? You’d likely reject your “proof” of this result on the grounds that the answer you’ve gotten is unreasonable. But, what makes it unreasonable? It conflicts with another claim that you are much more confident of: That the Earth is much larger than that!

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Or consider Zeno’s “proof” that is impossible. Here’s one of them:

Zeno’s Paradox: You want to get across a football field. Destination 1: To do so, you first have to go halfway across, to the 50-yard line. You now have 50 yards to go. Destination 2: To get across that, you first have to go halfway across, to the 25-yard line. You now have 25 yards to go. Destination 3: To get across that, you first have to go halfway across, to the 12.5 yard line (or between the 12 and 13, or whatever). You now have 12.5 yards to go. Destination 4: …. And so on, such that every you get to your new destination, you still have another halfway to go! But, then, there are an infinite number of these “new destinations” that you must get to before you can get to the other side of the field. And completing an infinite number of these is impossible. So, you never get to the other side of the field. In fact, no one ever gets ANY-where! Motion is impossible. Ta-da!

What is your response to this proof? Likely, you reject it. We COULD accept it. (Zeno did. He thought motion must be an illusion.) But, doing that would fly in the face of some of our most fundamental, common sense beliefs. So, we reject Zeno’s proof. SOMETHING must be wrong with it. At least one of his premises must be false.

This seems like an acceptable response. But, then, what is the difference between this response to Zeno (which was acceptable) and your response to your fellow juror (which was not)? Huemer notes three differences. Rejecting Zeno on the basis of a pre-existing belief has these three features, which the court case does not share:

(1) The evidence presented challenges a common sense belief; that is, it challenges a belief which (a) is universally accepted, (b) is taken for granted as true in ordinary life, and (c) would be ABSURD to reject—perhaps even a sign of insanity.

(The claim that motion is possible is a common sense belief. Meanwhile, that Sally is the killer is not.)

(2) Accepting the conclusion would be radically revisionary; that is, it would require the rejection or revision of a WIDE range of beliefs.

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(Rejecting the possibility of motion would require a revision of a large number of beliefs; e.g., that every time motion is perceived, it is merely an illusion. Rejecting the Sally’s guilt is a single, isolated belief.)

(3) The evidence presented is controversial.

(When presented with Zeno’s proofs, competent and reasonable experts will present reasons to reject them. When presented with the juror’s evidence of Marie’s guilt—presumably there is some!?—competent and reasonable people would not find them controversial, let’s assume.)

Well, if you think that this is an acceptable response to Zeno, then you ought to think Moore’s argument is an acceptable response to skepticism. For, the latter has these same three features!

(1) The skeptical hypothesis challenges a common sense belief. (2) Accepting skepticism would be radically revisionary. (3) The evidence which supports skepticism is controversial (e.g., the representationalist view of , the closure principle).

[Note: Not a Proof: Moore thinks skeptics are confused when they say that, in order to KNOW something, one needs to be able to PROVE it with 100% certainty. Moore claims that he KNOWS that “here is a hand” is true, even 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 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. He writes,

“How am I to prove now that ‘Here’s one hand, and here’s another’? I do not believe I can do it. In order to do it, I should need to prove for one thing, as Descartes pointed out, that I am not now dreaming. But how can I prove that I am not? I have, no doubt, conclusive reasons for asserting that I am not now dreaming … but that is a very different thing from being able to prove it. … I can know things which I cannot prove.”

Notice that, unlike Descartes, the emphasis here is NOT on certainty. We MIGHT insist that knowledge requires ABSOLUTE 100% CERTAINTY. But, that seems too strict. If we demanded absolute CERTAINTY for knowledge, then we would know very little. A weaker usage seems more in line with how we use the word ‘knowledge’ in everyday language. People CONSTANTLY take the sort of argument Moore has just provided as the only sort that is ever needed in order to establish some conclusion.

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For instance, imagine that you and your friend disagree about whether or not there is beer in the refrigerator. In order to settle the dispute, all that you need to do is open the refrigerator. “Here is one bottle of beer in the refrigerator,” you say, while holding up a bottle. “And here is another. Dispute settled.” What more could possibly be needed? It would be absurd of your friend to reply, “Yeah, but maybe we’re hallucinating, or an demon is deceiving us into thinking that you’re holding beer when you’re not. You can’t rule out the possibility that that’s beer. So, dispute NOT settled!”

Perhaps the court case example earlier was misleading. It does seem unjust to convict Sally if Marie hasn’t been ruled out yet—but that is assuming that Marie is a SUSPECT; i.e., there is some REASON to think that maybe Marie is guilty! Absent any such suspicion, there is no requirement to rule out the possibility that Marie is the culprit before convicting Sally (otherwise every jury would have to rule out ALL SEVEN BILLION human before it could ever justly convict anyone!). Similarly, the belief that you have hands would not be justified if you haven’t ruled out the possibility that you’re not a brain in a vat—ONLY in a scenario where we had some reason to think that we ARE brains in vats. Absent such a reason, there is no requirement to rule out this possibility before acquiring knowledge.

So: Do you know that you have hands? YES! Here is one. And here is another.]

[Some lingering worries: (1) Based on Moore’s reasoning, should we have rejected the Copernican Revolution? What do you think? (2) A BIV would be able to present EXACTLY the same evidence as Moore does: one hand, and then another. Is that not relevant?]

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