A Critical Analysis of Moore’s ‘Proof of an External World’ by Zachary Ong

In ‘Proof of an External World’, Moore seeks to prove the existence of things ‘external to our minds’ (Moore 1959). As our senses have been proven to be at least occasionally fallible, there exists the sceptic’s position that we cannot know the existence of an external world with certainty; we cannot provide proof to show that the things external to our minds are not a hallucination incongruent to reality. Moore attempts to provide such a proof, and, in doing so, prove the existence of an external world. However, despite widespread views to the contrary, Moore does not engage the sceptic on their own terms, knowing that it is impossible to prove empirical observations with certainty. Instead, Moore challenges the sceptic’s empirically invulnerable defense by establishing an opposing common sense position which is similarly immune to disproof.

Moore’s (paraphrased) argument begins: ‘here is a hand,’ as he gestures with one, ‘and here is another,’ as he gestures with the other. Then concludes that if these two hands do exist, then external things exist, and, therefore, the external world exists. Moore then claims this is not just a proof, but a rigorous one. The standards of such a proof are that the premise is both known and believed, and that the conclusion both follows and is different from the premise. Here, the premise is that there is a hand, the existence of which Moore claims to know and believe, and the conclusion is that there exists an external world.

It is immediately evident that the premise is different from the conclusion, and if we allow that the existence of external things, e.g. the hands, proves the existence of an external world, then the proof is sound. The only concern is whether Moore truly knows that his hands exist, or only believes that they do.

For the purposes of this work, knowledge is assumed to be true justified belief. The sceptic that we cannot claim to know something without both believing it and it being true, thus any empirical observation cannot be proven with certainty. The sceptic will claim that our sensory or phenomenal experiences have been known to be at least occasionally fallible, e.g. water refracting light to bend once-straight objects, hallucinations, parallel railway tracks that appear to converge in the distance. Yet, Moore claims that when he says‘here is a hand,’ he believes it to be true; he knows it exists, despite being unable to provide irrefutable proof.

Analogous to Moore’s supposed knowledge of the existence of his hands is his other claim that he has ‘conclusive reasons for asserting that I am not now dreaming; I have conclusive evidence that I am awake: but that is a very different thing from being able to prove it.’ (Moore 1959) Moore is saying that while we cannot prove that we are not dreaming instead of being awake, we can know it. I can lucidly recall waking up and the things I did today, as opposed to the unstable and inconsistent narratives of my dreamscapes. However, it is impossible to prove that we are awake at this moment with complete certainty. Similarly, when I present my hand and say: ‘here is my hand,’ I know that it is there, evidenced the notable consistencies of phenomenal experience. I feel light air currents bristle over my hair, as I always do; I see it with my eyes, as I always do; I can feel the extension of my arm to which it is connected, as I always do. But, none of these are a satisfactory proof for the sceptic, who might say that I am being deceived by an evil demon, or experiencing an illusion.

However, I do not believe that Moore intended to engage the sceptic on their own terms in this essay. In Hume’s Philosophy he says ‘It seems to me that [the sceptical] position must, in a certain sense, be quite incapable of disproof. So much must be granted to any sceptic who feels inclined to hold it. I can only prove that I do [know external facts], by assuming that in some particular instance, I actually do know one. That is to say, the so-called proof must assume the very thing which it pretends to prove. … And the sceptic can, with perfect internal consistency, deny that he does know any [external facts].’ (Moore 1909) I believe Moore understands that is it impossible to disprove the sceptic’s position, and hence knows it is fruitless to attempt certain proof, instead he emphasises that his position similarly immune to disproof. ‘They would say: ‘If you cannot prove your premise that here is one hand and here is another, then you do not know it.’ But you yourself have admitted that, if you did not know it, then your proof was not conclusive.’ (Moore 1959) Under these equal conditions for both his and the sceptic’s position, I believe that Moore is implying that, in the absence of proof for or against the sceptical position, it is simply more prudent or convincing to rely on empirical intuition. Prudence in that empirical observations are more conducive to forming foundational knowledge for posterity than scepticism; if we can never know with certainty, then we can never know, and we can never progress knowledge. Being convincing is ultimately subjective, but when I lucidly see a cup on a table, I am more inclined to believe it is exists than it doesn’t.

If Moore does not need to prove the existence of his hand, then his argument is logically sound. First, let us consider the sceptic’smodus ponens:

If I cannot tell the difference between wakefulness and dreaming, then I cannot be sure that there is a hand in front of me.
I cannot tell the difference between wakefulness and dreaming.
Q.E.D.: I cannot be sure that there is a hand in front of me.

Then, Moore’s modus tollens:

If I cannot tell the difference between wakefulness and dreaming, then I cannot be sure that there is a hand in front of me.
I am sure that there is a hand in front of me.
Q.E.D.: I can tell the difference between wakefulness and dreaming, and, therefore, the external world in which I experience wakefulness is real.

I believe Moore is saying that while he cannot prove that ‘I am sure that there is a hand in front of me’, it is more convincing than ‘I cannot tell the difference between wakefulness and dreaming.’ While his argument is rigorous, it is not watertight; it is obvious that the sceptic will still doubt the existence of Moore’s hand. However, it seems that Moore was never interested in pleasing the sceptic with this argument, knowing that the he could not contest them on their empirically immune terms.

Ultimately, I think Moore did not set out to overturn scepticism, but to show that common sense and empiricism, while not infallible, are prudent tools for foundations of knowledge. He acknowledges that while his premises and any similarly empirical claim cannot ever be proved, they can still be known through common sense and empiricism.

Zachary Ong is a first year student studying a dual bachelor of economics and arts at UQ.


Bibliography

Moore, G. E. 1959, Philosophical Papers.

Moore, G. E. 1939, Proof of an External World.

Moore, G. E. 1909, Hume’s Philosophy.

Weatherall, On G. E. Moore’s “Proof of an External World”, Paper, viewed 13th April 2015, <http://www.academia.edu/738604/On_G._E._Moores_Proof_of_an_External_World_>

Coliva, Scepticism and knowledge: Moore’s proof of an external world, Paper, viewed 13th April 2015, <http://www.academia.edu/874689/Scepticism_and_knowledge_Moore_s_proof_of_an_external_world>

Notes on Moore’s Proof of an External World, viewed 13th April 2015, <http://critique-of-pure-reason.com/notes-on-moores-proof-of-an-external-world/>

Photo by Elena Saharova.

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