Here is one hand
Here is one 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 amung philosophers.
A skeptical hypothesis, like "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.
It does so in the following form:
- If you don't know not H, you don't know O (O = anything)
- You don't know not H
---
- You don't know not 0
Moore's response is as follows:
- but I do know O
- if I don't know H, then I don't know O
---
- I must know H
Moore does not attack the skeptical argument, instead, he boldly claims that it is wrong, because its conclusion is unintuitive.
Historical description
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.
He 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 one 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, however. Moore gives in "Proof of an External World", three requirements for a good proof. (1) the premises must be different than 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.
Not surprisingly, not everyone inclined to skeptical doubts found Moore's method of argument entirely convincing; Moore, however, defends his argument on the 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. (In addition to fueling Moore's own work, the "Here is one hand" argument 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.)