Here is a hand

Here is a hand (or "aw come on") is the name of a philosophical argument created by George Edward Moore against Philosophical skepticism and in support of common sense. The argument has become famous among philosophers.

Introduction

Skeptical hypotheses, such as "you may be dreaming" or " the world is 5 minutes old", create a situation where it is not possible to know that anything in the world exists. They do so in the following form:

The Skeptical Argument

• If you don't know not H, you don't know not O (where O = anything)
• You don't know not H

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• You don't know not O (in other words, you can't be sure about O)

Moore's response is as follows:

• But I do know O
• If I don't know H, then I don't know O

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• I must know H

Moore does not attack the skeptical argument, instead, he boldly claims that it is wrong, because its conclusion is unintuitive.

Explanation

Moore famously put the point into dramatic relief with his 1939 essay "Proof of an External World", in which he gave a common sense argument against skepticism by raising his right hand and saying "Here is a hand," and then raising his left and saying "And here is another," then concluding that there are at least two external objects in the world, and therefore that he knows (by this argument) that an external world exists.

Moore's argument is not simply a flippant response to the skeptic. Moore gives in "Proof of an External World", three requirements for a good proof. (1) the premises must be different from the conclusion, (2) the premises must be demonstrated, and (3) the conclusion must follow from the premises. He claims that his proof of an external world meets those three criteria.

In his 1925 essay "A Defence of Common Sense" he argued against idealism and skepticism toward the external world on the grounds that they could not give reasons to accept their metaphysical premises that were more plausible than the reasons we have to accept the common sense claims about our knowledge of the world that skeptics and idealists must deny. In other words, he is more willing to believe that he has a hand than believe the premises of a strange argument in a University classroom. "I do not think it is rational to be as certain of any one of these ... propositions".

Not surprisingly, not everyone inclined to skeptical doubts found Moore's method of argument entirely convincing; Moore, however, defends his argument on the (surprisingly simple) grounds that skeptical arguments seem invariably to require an appeal to "philosophical intuitions" that we have considerably less reason to accept than we have for the common sense claims that they supposedly refute.

Logic

The skeptical argument takes the form of Modus Ponens: If A then B. A. Therefore B.

Moore's argument flips the Modus Ponens structure into a Modus Tollens: If A then B. Not B. Therefore not A.
"one man's modus ponens is another man's modus tollens" (Dretske 1995 ).

Effect

Appeals of this type are subsequently often called "Moorean facts". "A Moorean fact [is] one of those things that we know better than we know the premises of any philosophical argument to the contrary".

The "here is one hand" idea, in addition to fueling Moore's own work, also deeply influenced Wittgenstein, who spent his last weeks working out a new approach to Moore's argument in the remarks that were published posthumously as On Certainty.

Although perhaps not a supplement to Moore's argument, it has been mentioned in undergraduate philosophy classes that Moore famously mistook his own sense perception once in a lecture. Whereby he claimed "there is a window" pointing at a curtain in a gymnasium, but when a student pulled the curtain away it was merely a wall. Whether this is a philosophical urban legend or not, there is little doubt that optical illusions and hallucinations can cause unreliable sense perceptions.

Criticism

The argument is purported to be an answer against skepticism, but only if one accepts a single form of skepticism as the sum total of the school. While it provides some answer to Academic skepticism, it is not able to counter more strictly pyrrhonean skeptics who maintain equipollence rather than insisting that something definitely is not true or is not known. Additionally, the definition of "knowledge" is historically contested amongst philosophers. It may be that by claiming to "know" of the existence of two objects in the external world, Moore is actually begging the question or, worse, falling victim to an infinite regress.

See also

• Simulated reality

External links

• Kelly, Thomas. Moorean Facts and Belief Revision, or Can the Skeptic Win?. Princeton University. Forthcoming in John Hawthorne (ed.), Philosophical Perspectives, vol.19: Epistemology. [1]