What do hands do? For one English philosopher, George Edward Moore, hands are a living proof of the external world.

Moore: Proof of an External World

Before any formal proof, lies the tedious task of clarifying the concept in question. This occupies a major part of the Moore’s paper, Proof of an External World.

Moore started building a definition of the external world by referring to Immanuel Kant’s Critique of Pure Reason. Kant started by referring to the external word as ‘things outside of us’. Recognising then, that objects can be external in the ’empirical’ or ‘transcendental’ sense, Kant refined the definition to ‘things which are to be met with in space’ for empirically external world.

Thing outside of us: Transcendental vs Empirical

Another notation that Kant used interchangeably for the empirically external world is ‘presented in space’. Moore, after a meticulous examination, concluded that the two are different, that ‘things which are to be met with in space’ may not be ‘presented in space’, and vice versa.

A number of examples were given. After-images and bodily pains, for example, do seem to be ‘presented in space’ yet are nowhere to be ‘met with in space’.

On the other hand, there is no requirement that ‘things which are to be met with in space’ must be in fact ‘met with in space’. Therefore, there are also things ‘which are to be met with in space’ yet are not ‘presented in space’. These are, as Kant described, objects of possible experience, and are not objects of actual experience.

Moore further noted, by contrasting the concept of ‘to be met with in space’ with ‘external to our minds’, that certain things that are ‘presented in space’, such as after-images and bodily pains, require oneself having a subjective experience, whereas other things that are ‘presented in space’ do not require such.

Empirically external things: Things to be met with in space vs Presented in space whether subjectively or objectively experienced

While further refining of this definition of the external world is possible, recognising that defining the external world as ‘things which are met with in space’ is sufficient for his purpose of proving the external world, Moore moved on to say:

“By holding up my two hands, and saying, as I make a certain gesture with the right hand, ‘Here is one hand’, and adding, as I make a certain gesture with the left, ‘and here is another’. And if, by doing this, I have proved ipso facto the existence of external things, you will all see that I can also do it now in numbers of other ways: there is no need to multiply examples.” – G. E. Moore, Proof of an External World.

Crispin Wright: Transmission Faulure

Like most philosophical discussions, Moore’s assertion was not without doubts. Crispin Wright, in his (Anti-)Sceptics Simple and Subtle: G. E. Moore and John McDowell, exposed a flaw in Moore’s logic.

Wright started by constructing Moore’s argument:

(1) Here is a hand
(2) There is a material world
(since any hand is a material object existing in space)

Wright claimed that Moore presupposed that external world exists before starting the argument. Otherwise, his perceptual, namely visual, experience, could not have provided him a warrant for inferring from Moore (1): Here are two hands, to Moore (3): There is an external world, for there are many scenarios, in which one can see hands, without it leading explicitly to the conclusion that the hand, and therefore, the external world exists as ‘things which are met with in space’.

Imagine one is dreaming, or is in an illusional state because of spending too much time reading philosophical paper, and is making the same argument as Moore did. Hand is to be seen, yet in this dream or illusional universe, there are no ‘things which are to be met with in space’, nor an external world.

Hence, to go from there being hands to there being external world, or as Wright said, to transmit the warrant from the former to the later, Moore would need, in Wright’s words, an antecedent warrant, for the belief that the external word exists. Without such antecedent warrant, Wright suggested that Moore proof exhibited ‘transmission failure’.

That is to say, Moore needed a warrant for the belief that the external world exists, in order to transmit a warrant from there being hands, to there being external world. This evidently is a vicious feedback loop, or formally, circularity.

Transmission failure in Moore's argument

Moore intended his argument to be a response to scepticism which doubts the external world. Under Wright’s diagnoses, it seems that Moore, ironically, proved that inference cannot transmit warrant, from perceptually warranted beliefs, about any material ob­ject, to the belief in the existence of the external world.

James Pryor: Dialectic Ineffectiveness

Entered James Pryor, with his What’s Wrong with Moore’s Argument. While Pryor noted that philosophers have reasons to challenge whether Moore has perceptual justification to believe he has hands or, like Wright pointed out, whether this warrant to believe that he has hands transmits to the conclusion that there is an external world, Pryor put forth a different view.

Pryor meticulously investigated into the structure of justification, the different kinds of epistemic dependence between premise and conclusion, and the process of reasoning and doubt, justified or otherwise.

Pryor then, disagreeing with Wright, suggested that Moore’s perceptual justification to believe he has hands has prima facie justification, as a result of Moore having the phenomenology of seeming to ascertain his perceptual experience, and hence does not require antecedent justification for the belief of an external world.

There is however one aspect where Pryor found Moore’s argument falls short, that Moore’s argument lacks dialectic effectiveness against scepticism, which doubts the external world. Be there no falsity in the justificatory structure or the reasoning in Moore’s argument, assuming that our perceptual experience justifies perceptual belief is not something a sceptic would agree to begin with.

Dialectic ineffectiveness in Moore's argument

And, in a larger sense, Pryor noted that Moore’s argument fell short on its responsibilities, as a philosophical response to scepticism, by failing to diagnose, criticise and expose the flaws in the skeptic’s reasoning.

Annalisa Coliva: Warrant Assumed

Annalisa Coliva has yet a different view than Wright or Pryor.

Before proposing her view, Coliva, in her Proof of an external world: transmission failure, begging the question or dialectical ineffectiveness? Moore, Wright and Pryor, examined Moore’s argument as well as the views of Wright and Pryor, and by carefully comparing the two, Coliva brought to light, some subtleties that were hiding in-between the lines.

Idealism or Skepticism?

First thing Coliva did was to correct a misperception which was held by both Wright and Pryor among many, that Moore’s argument was directed at scepticism, which doubts the external world.

Coliva reconstructed Moore’s argument according Moore’s original writing:


(1) Here’s one hand; then he hides it.
Then, following the same procedure, he says:

(2) Here’s another; then he hides it.
Finally, without showing his hands again, he concludes:

(3) There are two human hands at present.

Since the conclusion concerns the existence of objects which can be encountered in space, despite the fact that they are not currently perceived, and that, therefore, exist independently of our minds, Moore claims that (3) entails:

(4) The external world exists.

Coliva believed, which Moore a few years after his argument also claimed, that Moore’s argument was directed instead at idealism, which believes things exists in and only in perception. The essence of which is well captured in the Irish philosopher George Berkeley’s famous quote:

‘esse is percipi (to be is to be perceived)’ – George Berkeley

Nonetheless, Moore’s argument still does not prevail even after shifting the crosshair from scepticism to idealism, as Coliva then pointed out, for there is no proof that Moore’s hands continue to exist when they are hidden and not perceived by anyone.

Therefore Coliva suggested that there was a hidden premise between Moore* (3) and Moore* (4):

(*) The hands presented in (1) and (2) continue to exist when they are not perceived.

This is the premise that idealist is committed to reject. Once revealed, it demonstrates the question-begging nature of Moore’s argument, that while the argument being logically correct, it tacitly assumes, as a premise, the negation either of the opponent’s thesis, or of something to which the opponent is committed. This renders the argument dialectically ineffective.

Logical Proof or Epistemic Proof?

Coliva then moved on to look at two different notions of a proof:

Logical Proof Epistemic Proof
Premises Logically Lead to Conclusion Required Required
Known or Justified Premises Not Required Required
Enlarge Knowledge Not Required Required

Since Moore claimed that he knew the premises to be true, he was im­plicitly committed to the epistemic reading of his argument, which as a result led to his argument being read as anti-sceptical by both Wright and Pryor among many.

From there, Coliva, by analysing Moore’s argument as an epistemic proof, rejected Pryor’s claim that ‘transmission failure’ was the same as ‘question-begging’ for there is one subtle difference:

Question-Begging Transmission Failure
Premises Contain Negation of Opponent’s Thesis Yes Yes
Dialectically Ineffective Yes Yes
Warrant for Premises Depend on Antecedent Warrant for Conclusion No Yes

This difference between a question-begging argument and an argument with transmission failure, that the warrant for the premises depend on there being an antecedent warrant for the conclusion, is what makes the former a good argument, and the latter a bad argument, as an epistemic proof.

Sceptic or Agnostic?

Coliva then marched on to imagine a sceptic’s position. Disagreeing with Pryor, Coliva believed the best possible sceptic would not hold false that there being an external world, rather, the sceptic will be agnostic about it.

As a result, there being Moore’s hands will not be rejected by an agnostic as false premise nor will it be accepted as true. An agnostic will instead view the premise of there being Moore’s hands as unwarrantable.

Sceptic Agnostic
There being External World Reject It Agnostic about It
There being Moore’s Hands False Premise Unwarrantable Premise

Against an agnostic, Coliva noted, Pryor’s reading of Moore’s argument will be begging the question, since Pryor assumed that Moore had prima facie justification for the premise of there being hands, as a result of him having the phenomenology of seeming to ascertain his perceptual experience, which an agnostic questions.

Against a sceptic, an idealist or an agnostic, Moore’s argument is not dialectically effective.

An Intermediate View

After analysing both Wright’s and Pryor’s views in details, Coliva suggested the dispute between the two, perhaps, lies in whether our ordinary belief-forming procedures need to be warranted in order to transmit warrant to the resulting belief.

Wright said yes and Pryor said no. Coliva instead proposed a third and intermediate view.

Wright Coliva Pryor
Perceptual Experience Warrants Empirical Belief Requires Antecedent Warrant Warrant Assumed Unless There Exists Defeating Evidence Yes Unless There Exists Defeating Evidence

Reassessing Moore’s argument with this intermediate view, that the belief in an external world is assumed to be warranted, Coliva admitted that Moore’s argument will still fail due to transmission failure. Inference cannot transmit a warrant from there being hands to there being external world, given the belief in an external world is assumed to be warranted.

Wright is, Coliva concluded, right in his diagnosis of the failure of Moore’s proof after all.

An End Note

Even if scepticism is right, that there is no external world, that I am deceived by an evil demon, or that I am a brain in a vat, so long as I do not know if there is or there will be any world other than this, this life, unreal may it be, is still my only life.

I only have one shot, what more reason do I need to make the most out of it?