George Edward Moore
George Edward Moore, also known as G.E. Moore, (November 4, 1873 - October 24, 1958) was a distinguished and hugely influential English philosopher who was educated and taught at Cambridge University. He was, with Bertrand Russell, Wittgenstein, and (before them) Frege, one of the fathers of the analytic philosophy tradition that now predominates in the English-speaking world. Moore was best known for his advocacy of common sense, his ethical non-naturalism, and his very clear, circumspect writing style. He was a methodical and careful philosopher. He is very much a "philosopher's philosopher"--influential among and greatly respected by other philosophers, but relatively unknown to nonphilosophers (unlike his friend and colleague Russell).
Moore's most famous essays are "The Refutation of Idealism", "A Defence of Common Sense", and "A Proof of the External World" each of which can be found in his collection of papers, Philosophical Papers. He argued against skepticism about the external world by, famously, raising his right hand and saying 'here is a hand', then raising his left hand and saying 'here is a hand', conluding that there are at least two material objects in the world and therefore, there is an external world.
Moore is also well-known for the so-called "open question argument," which is contained in his (also greatly influential) Principia Ethica. The Principia is one of the main inspirations of the movement against ethical naturalism (see ethical non-naturalism) and is partly responsible for the twentieth-century concern with meta-ethics.
He also first drew attention to what is now called "Moore's Paradox", the peculiar inconsistency involved in uttering a sentence like "It is raining but I don't believe that it is." This puzzle inspired a great deal of work by Ludwig Wittgenstein.