"How far is anyone justified, be he an authority or a layman, in expressing or trying to express in terms of music (in sounds, if you like) the value of anything, material, moral, intellectual, or spiritual, which is usually expressed in terms other than music? How far afield can music go and keep honest as well as reasonable or artistic? Is it a matter limited only by the composer’s power or expressing what lies in his subjective or objective consciousness? Or is it limited by any limitations of the composer?"If you have not read it, I highly recommend reading Charles Ives’ Essays Before a Sonata. It's in the public domain, and there’s a PDF of the 1920 Knickerbocker Press edition in the Petrucci Library.
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