Do You Know That You Have Hands?

The natural response to the question Do you know that you have hands? is Of course. Our knowledge that we have hands seems to be one of our most basic and certain items of knowledge, and so concluding that we don t know such a thing would mean concluding (against all our intuitions) that we know almost nothing. This is exactly what the sceptic does, however. By outlining a sceptical situation in which everything external to us is not as it appears to be, he throws into doubt all our knowledge of such external things. Many philosophers have sought to defend our knowledge of the external world against the sceptic s challenge, but almost all of these suffer from significant weaknesses. In this essay, I will argue that the contextualist response [ET1] is most effective, allowing you to maintain that at least in some sense you know that you have hands.

Sceptical arguments can take many forms but, as Crispin Wright puts it, they typically proceed via presentation of some large, purportedly untestable possibility which is somehow supposed to undermine a whole region of what we had fancied to be knowledge. [1] They can do this because, as Robert Nozick points out, we know mediately Our thinking or believing that some fact p holds is connected somehow to the fact that p, but is not itself identical with that fact. [2] The sceptic establishes his conclusion by pointing out that the intermediate stages may produce our belief that p, without p holding at the other end. So, to take one example, the sceptic might suggest that you are not a human being on planet earth but a brain in a vat being electrochemically stimulated on Alpha Centauri to believe that you are a human being on planet earth[3]. In this sceptical situation, all your beliefs about the external world are false, including your belief that you have hands.

As mentioned above, philosophers have made many attempts to combat these sceptical hypotheses. One of the most famous of recent times is that made by G.E. Moore in Proof of an External World . Moore s argument proceeds as follows:

1. Here is one hand.

2. And here is another.

C. Therefore, two human hands exist. [4]

Moore s conclusion plainly follows from his premises, but the sceptic will not be satisfied by the argument as it stands, for Moore appears to be begging the question with his first and second premises. That Moore can know these premises is exactly the kind of assumption that the sceptical hypothesis calls into question and so Moore seems to be assuming what needs to be proved.

Moore concedes that he cannot prove his first two premises in the way that the sceptic requires him to. He maintains, however, that his inability to do so does not count against his knowledge of the two premises. On the contrary, he writes, I can know things which I cannot prove and among things which I certainly did know, even if (as I think) I could not prove them, were the premises of my two proofs. [5] This comment suggests an interpretation of Moore s proof in which the sceptical argument is regarded as a kind of reductio ad absurdum on itself. The sceptical argument takes the form of a modus ponens, and proceeds as follows:

1. You do not know that you are not a brain in a vat.

2. If you do not know that you are not a brain in a vat, you do not know that you have hands.

C. You do not know that you have hands.

The first premise is very plausible because, ex hypothesi, there is no way of distinguishing between the situation in which you are a brain in a vat and the situation in which you are a human being on earth (because your experiences are exactly the same in both situations). The second premise is very plausible because if you were a brain in a vat, you would not have hands. The conclusion follows from the premises.

On the above interpretation of Moore s argument, the implausibility of the sceptic s conclusion outweighs the plausibility of his premises. Although both the sceptic s premises are very plausible, they lead to an overwhelmingly implausible conclusion and so, Moore seems to be saying, we should run the argument in reverse. That is, we should take the contrary of the sceptic s conclusion as a premise and argue to the contrary of the sceptic s premise, as so:

1. You know that you have hands.

2. If you know that you have hands, you know that you are not a brain in a vat.

C. You know that you are not a brain in a vat.

Moore writes in Certainty that the sceptic s method of reasoning cuts both ways and that the one argument is just as good as the other. [6] David Lewis summarises this response nicely, writing that our knowledge that we have hands is a Moorean fact It is one of those things that we know better than we know the premises of any philosophical argument to the contrary. [7] So, Moore maintains, you can know that you have hands, simply because your knowing such a thing is more plausible than the sceptical argument to the contrary. For this reason, he contends, your knowledge that you have hands does not require proof.

The sceptic, though, is unlikely to accept Moore s argument. He can point out, as both Barry Stroud and Crispin Wright do, that Moore seems to mischaracterise the sceptical argument. Moore fails to recognise that the reasonableness of his inference from Here is one hand and here is another to Two human hands exist depends on the prior reasonableness of his conclusion, You know that you are not a brain in a vat. Knowledge of the first does not begin to provide support for the second unless it is antecedently reasonable to accept the third. [8] So it is illegitimate of Moore to flip the sceptical argument on its head. He cannot run the argument in reverse as if it were a straightforward inference from first premise to second premise to conclusion.

Stroud illustrates this idea through his example of the detective and the apprentice. Suppose a murder has been committed in a country mansion, and a short list of suspects has been presented to the detective s apprentice. Stroud writes that the apprentice has eliminated all suspects from the list except for the butler, and so says to the detective that the butler is the murderer. The detective points out, however, that it is not certain that the list includes all potential suspects, and so responds to the apprentice, Since you don t know that the list is complete, it follows that you don t know that the butler did it. [9] After all, the murderer could be someone who is not on the list. In this case, the apprentice would be wrong to respond that the detective s form of reasoning cuts both ways. He could not say, I can just as well argue: since I do know that the butler did it, it follows that I do know that the list is complete. [10] Rather, the apprentice must give other reasons for his belief that the list is complete. In the same way, Stroud suggests, Moore must give other reasons for his belief that the brain-in-a-vat possibility does not obtain.

This is something that Moore cannot do. He writes in Proof of an External World that he has conclusive evidence and conclusive reasons for believing that he is not a brain in a vat, but concedes that he could not tell you what all [his] evidence is. [11] He seems to be appealing to our intuitive belief that we are not brains in vats, but this intuitive belief cannot serve as evidence for itself. After all, it is perfectly possible that we hold that same intuitive belief in the brain-in-a-vat situation it might be that the scientists in charge electrochemically stimulate you to believe that you are not a brain in a vat. Moore s response to the sceptic is unsuccessful, then. In order to justifiably conclude that you can know you have hands without being able to prove it, Moore would have to give satisfactory independent reasons for believing the brain-in-a-vat possibility does not obtain, and this is something he fails to do.

The failure of Moore s response to rescue our knowledge that we have hands might lead us to accept that the sceptic is successful in his challenge. That is, the sceptical argument proves that you cannot strictly know that you have hands. By adopting a contextualist response, however, we can minimise the amount of disruption the sceptic does to our ordinary beliefs and practices. Contextualists believe that our claim to knowledge is dependent on the context in which our knowledge is being examined[ET2] . So, for instance, Norman Malcolm makes a distinction between strong and weak [12] knowledge in order to explain the intuitive strength of the sceptic s argument. The sceptic s argument shows that you don t have knowledge in the strong or philosophical sense of the word, but, he argues, your claim to ordinary knowledge is unaffected. Similarly, Lewis writes of knowledge, S knows proposition P if and only if S s evidence eliminates every possibility in which not-P Psst! except for those possibilities that we are properly ignoring. [13] By possibilities that we are properly ignoring, Lewis means hypothetical situations that cannot be classed as relevant alternatives. In the context of ordinary conversation, the possibility that you are a brain in a vat does not count as a relevant alternative to your knowledge that you have hands. By introducing such a possibility, the sceptic causes what was previously an irrelevant alternative to become relevant, by what Lewis calls the rule of attention, [14] and so shifts the context into one in which you do not qualify as a knower. So the contextualist can maintain that, though the sceptic proves you don t know you have hands in the strong sense, your claim to ordinary knowledge of this proposition is unaffected. In most contexts, you can rightly claim to know that you have hands.

Two criticisms commonly levelled against the contextualist are as follows. The first is that distinguishing between types of knowledge solely to thwart the sceptic is unacceptably ad hoc. In response to this objection, the contextualist can point out that it is not just in response to scepticism that context comes into play many of our ordinary attributions of knowledge appear to be context-dependent. If a stranger told you he knew the next train pulling into the station stopped in Birmingham, you might accept his knowledge, but if you had an important meeting you had to get to in Birmingham, you would probably want to confirm that fact with the conductor.

The second criticism directed against the contextualist is that they concede too much to the sceptic, since they accept that, at least in some sense, you do not know that you have hands. However, how significant a concession this is deemed to be depends on how important one regards strong knowledge to be. In any case, no response to the sceptic thus far has established incontestably that you can know you have hands. Indeed, it is difficult to even conceive of what such a response would be like. At this point at least, the contextualist response to the sceptic is the best one at our disposal[ET3] .

In conclusion, then, we should side with the contextualist in judging that you cannot know that you have hands in any strong, philosophical sense the sceptical argument establishes that it is always possible that you are incorrect in supposing such a thing. However, this argument does not weigh against your claim to know that you have hands in ordinary, conversational contexts. You can know, at least in some weak sense[ET4] , that you have hands.

[1] Facts and Certainty , Crispin Wright, in Proceedings of the British Academy 71, 1985

[2] Knowledge and Scepticism , Robert Nozick, in Philosophical Explanations, 1981

[3] Ibid.

[4] Proof of an External World , G.E. Moore, Philosophical Papers, 1959

[5] Ibid.

[6] Certainty , G.E. Moore, in G.E. Moore: Selected Writings, edited by Thomas Baldwin, 1993

[7] Elusive Knowledge , David Lewis, in Australasian Journal of Philosophy 74, 1996

[8] Facts and Certainty , Crispin Wright, in Proceedings of the British Academy 71, 1985

[9] G.E. Moore and Scepticism: Internal and External'#146, Barry Stroud, in The Significance of Philosophical Scepticism, 1984

[10] Ibid.

[11] Proof of an External World , G.E. Moore, Philosophical Papers, 1959

[12] Knowledge and Belief , Norman Malcolm, in Mind 61, 1952

[13] Elusive Knowledge , David Lewis, in Australasian Journal of Philosophy 74, 1996

[14] Elusive Knowledge , David Lewis, in Australasian Journal of Philosophy 74, 1996