Internet Encyclopedia of Philosophy
“We invent by intuition, though we prove by logic.”
Eminent Indians (1947)
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Sarvepalli Radhakrishnan 84
Indian philosopher and statesman who was the first Vice Pre… 1888–1975Related quotes
“It is through science that we prove, but through intuition that we discover.”
                                        
                                        From his "Autobiographische Skizze" (18 April 1955), original German version  here http://philoscience.unibe.ch/documents/kursarchiv/WS99/Skizze.pdf. Translation from Subtle is the Lord: The Science and the Life of Albert Einstein by Abraham Pais (1982),  p. 131 http://books.google.com/books?id=U2mO4nUunuwC&lpg=PP1&pg=PA131#v=onepage&q&f=false. Pais notes that when he said "during that year", he was referring to some time between October 1895 and early fall 1896.
Variant: "Innovation is not the product of logical thought, even though the final product is tied to a logical structure."
Original German version: Während dieses Jahres in Aarau kam mir die Frage: Wenn man einer Lichtwelle mit Lichtgeschwindigkeit nachläuft, so würde man ein zeitunabhängiges Wellenfeld vor sich haben. So etwas scheint es aber doch nicht zu geben! Dies war das erste kindliche Gedanken-Experiment, das mit der speziellen Relativitätstheorie zu tun hat. Das Erfinden ist kein Werk des logischen Denkens, wenn auch das Endprodukt an die logische Gestalt gebunden ist. ("Autobiographische Skizze", p. 10) 
1950s 
Context: During that year in Aarau the question came to me: If one runs after a light wave with [a velocity equal to the] light velocity, then one would encounter a time-independent wavefield. However, something like that does not seem to exist! This was the first juvenile thought experiment which has to do with the special theory of relativity. Invention is not the product of logical thought, even though the final product is tied to a logical structure.
                                    
                                        
                                         Ahmadinejad on His Proposal for a Jewish State in Europe and on Iran's Nuclear Energy http://www.memritv.org/Transcript.asp?P1=987 Jan. 2006. 
2006
                                    
                                        
                                        Variant: Until writing was invented, we lived in acoustic space: boundless, directionless, horizonless, the dark of the mind, the world of emotion, primordial intuition, terror. Speech is a social chart of this bog. (p. 13) 
Source: 1960s, Counterblast (1969), p. 13
                                    
Gottlob Frege in: Dagobert David Runes (1962). Readings in epistemology, theory of knowledge and dialectics. p. 334
"The Methodology of Positive Economics" (1953)