Here is a hand
Encyclopedia
Here is a hand is the name of a philosophical argument
created by George Edward Moore
against philosophical skepticism
and in support of common sense
:
and Proof of an External World. He posed skeptical hypotheses, such as "you may be dreaming
" or "the world is 5 minutes old", creating a situation where it is not possible to know that anything in the world exists. These hypotheses take the following form:
The skeptical argument
Where S is a subject, sp is a skeptical possibility, such as the brain in a vat
hypothesis, and q is a knowledge claim about the world:
Moore's response
Moore does not attack the skeptical premise; instead, he reverses the argument from being in the form of modus ponens
to modus tollens
. This logical maneuver is often called a G. E. Moore shift or a Moorean shift.
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, those inclined to skeptical doubts often found Moore's method of argument not 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.
:
Moore's argument flips the modus ponens structure into a modus tollens
:
This illustrates Fred Dretske
's aphorism that "[o]ne man's modus ponens is another man's modus tollens"
The "here is one hand" idea, in addition to fueling Moore's own work, deeply influenced Ludwig Wittgenstein
, whose last writings were devoted to a new approach to Moore's argument. These remarks were published posthumously as On Certainty
.
Argument
In philosophy and logic, an argument is an attempt to persuade someone of something, or give evidence or reasons for accepting a particular conclusion.Argument may also refer to:-Mathematics and computer science:...
created by George Edward Moore
George Edward Moore
George Edward Moore OM, was an English philosopher. He was, with Bertrand Russell, Ludwig Wittgenstein, and Gottlob Frege, one of the founders of the analytic tradition in philosophy...
against philosophical skepticism
Philosophical skepticism
Philosophical skepticism is both a philosophical school of thought and a method that crosses disciplines and cultures. Many skeptics critically examine the meaning systems of their times, and this examination often results in a position of ambiguity or doubt...
and in support of common sense
Common sense
Common sense is defined by Merriam-Webster as, "sound and prudent judgment based on a simple perception of the situation or facts." Thus, "common sense" equates to the knowledge and experience which most people already have, or which the person using the term believes that they do or should have...
:
- This is a hand.
- Here is another hand.
- There are at least two external objects in the world.
- Therefore an external world exists.
Introduction
G. E. Moore (1873—1958) wrote A Defence of Common SenseA Defence of Common Sense
A Defence of Common Sense is an influential 1925 essay by philosopher G. E. Moore. In it, he attempts to refute skepticism by arguing that at least some of our beliefs about the world are absolutely certain...
and Proof of an External World. He posed skeptical hypotheses, such as "you may be dreaming
Dream argument
The dream argument is the postulation that the act of dreaming provides preliminary evidence that the senses we trust to distinguish reality from illusion should not be fully trusted, and therefore any state that is dependent on our senses should at the very least be carefully examined and...
" or "the world is 5 minutes old", creating a situation where it is not possible to know that anything in the world exists. These hypotheses take the following form:
The skeptical argument
Where S is a subject, sp is a skeptical possibility, such as the brain in a vat
Brain in a vat
In philosophy, the brain in a vat is an element used in a variety of thought experiments intended to draw out certain features of our ideas of knowledge, reality, truth, mind, and meaning...
hypothesis, and q is a knowledge claim about the world:
- If S doesn't know that not-sp, then S doesn't know that q
- S doesn't know that not-sp
- Therefore, S doesn't know that q
Moore's response
- If S doesn't know that not-sp, then S doesn't know that q
- S knows that q
- Therefore, S knows that not-sp
Moore does not attack the skeptical premise; instead, he reverses the argument from being in the form of modus ponens
Modus ponens
In classical logic, modus ponendo ponens or implication elimination is a valid, simple argument form. It is related to another valid form of argument, modus tollens. Both Modus Ponens and Modus Tollens can be mistakenly used when proving arguments...
to modus tollens
Modus tollens
In classical logic, modus tollens has the following argument form:- Formal notation :...
. This logical maneuver is often called a G. E. Moore shift or a Moorean shift.
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". Here, Moore is taking his knowledge claim (q) to be that he has two hands, and without rejecting the skeptic's premise, proves that we can know the skeptical possibility (sp) to be not true.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
A Defence of Common Sense
A Defence of Common Sense is an influential 1925 essay by philosopher G. E. Moore. In it, he attempts to refute skepticism by arguing that at least some of our beliefs about the world are absolutely certain...
he argued against idealism and skepticism
Skepticism
Skepticism has many definitions, but generally refers to any questioning attitude towards knowledge, facts, or opinions/beliefs stated as facts, or doubt regarding claims that are taken for granted elsewhere...
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, those inclined to skeptical doubts often found Moore's method of argument not 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.
Logical form
The skeptical argument takes the form of modus ponensModus ponens
In classical logic, modus ponendo ponens or implication elimination is a valid, simple argument form. It is related to another valid form of argument, modus tollens. Both Modus Ponens and Modus Tollens can be mistakenly used when proving arguments...
:
- If A then B.
- A.
- Therefore B.
Moore's argument flips the modus ponens structure into a modus tollens
Modus tollens
In classical logic, modus tollens has the following argument form:- Formal notation :...
:
- If A then B.
- Not B.
- Therefore not A.
This illustrates Fred Dretske
Fred Dretske
Frederick Irwin Dretske is a philosopher noted for his contributions to epistemology and the philosophy of mind. His more recent work centers on conscious experience and self-knowledge. Additionally, he was awarded the Jean Nicod Prize in 1994...
's aphorism that "[o]ne man's modus ponens is another man's modus tollens"
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, deeply influenced Ludwig Wittgenstein
Ludwig Wittgenstein
Ludwig Josef Johann Wittgenstein was an Austrian philosopher who worked primarily in logic, the philosophy of mathematics, the philosophy of mind, and the philosophy of language. He was professor in philosophy at the University of Cambridge from 1939 until 1947...
, whose last writings were devoted to a new approach to Moore's argument. These remarks were published posthumously as On Certainty
On Certainty
On Certainty is a philosophical book composed from the notes written by Ludwig Wittgenstein just prior to his death. Some of the notes were left at the home of G. E. M...
.
See also
- Samuel JohnsonSamuel JohnsonSamuel Johnson , often referred to as Dr. Johnson, was an English author who made lasting contributions to English literature as a poet, essayist, moralist, literary critic, biographer, editor and lexicographer...
, to whom is attributed the act of hitting a rock with his foot as a "refutation" of immaterialism
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.