“Why did Mozart compose music?”
Response when asked why he chose to do medical research rather than be a practicing physician, as quoted in The Polio Man : The Story of Dr. Jonas Salk (1961) by John Rowland, p. 23
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Jonas Salk 47
Inventor of polio vaccine 1914–1995Related quotes
Source: The Frontiers of Meaning: Three Informal Lectures on Music (1994), Ch. 2 : How to Become Immortal

Answering why he wrote an independent scripting language for Gambas. Quoted from FOSDEM interview, " http://www.madeasy.de/7/benoit.htm http://www.madeasy.de/7/benoit.htm" Mad Easy (2005-02-14)

Mozart brauchte kein Programm für seine Musik. Er musizierte und sang mit der göttlichen Leichtigkeit eines Kindes.
Michael: a German fate in diary notes (1926)

Quotes from Stefan Zweigs's posthumous memoire, The World of Yesterday. Zweig worked with Strauss closely on the opera The Silent Woman in the period 1931-1934 and got to know him well.
Other sources

“The composer makes plans, music laughs.”
Quoted in Give My Regards to Eighth Street: Collected Writings of Morton Feldman, ISBN 1878972316.

telegraph.co.uk http://www.telegraph.co.uk/culture/music/classicalmusic/9467708/Pianist-Valentina-Lisitsa-interview-with-the-YouTube-star.html