As to what concerns the knotty question in general of how far instrumental music may go in the representation of thoughts and events, many are here too anxious in their attitude. We are certainly wrong if we believe that composers set out pen and paper to realize the miserable intention of expressing, describing, or painting this or that. Yet let us not place too low a value on fortuitous external influences and impressions. Unconsciously alongside the musical fantasy an idea is often continuously active, alongside the car the eye, and this, the organ always active, then holds fast amidst the sounds and tones to certain contours that can condense and develop themselves into distinct forms with the advancing music. Now the more the thoughts or images produced with the tones carry within them elements related to music, the more poetic or plastic in expression the composition will be, — and the more fantastic or sharper the conception of the musician is, the more his work will exalt or arrest us. . . . Indeed even smaller, more particular images can lend so charming and definite a character to music that one is astonished at how it is able to express such traits. Thus a composer once told me that while he was writing, the image of a butterfly swimming along on a leaf in a brook intruded itself upon him; this had given the little piece the delicacy and naiveté that somehow only the image may possess in reality.

In this fine genre painting Franz Schubert in particular was a master, and I cannot forbear adducing from my experience how once during a Schubert March the friend with whom I was playing answered my question about whether he did not see very specific figures before him: “Indeed! I found myself in Seville, but over a hundred years ago, amidst Dons and Doñas walking up and down, wearing dresses with trains, pointed shoes, pointed swords,” and so on. Strangely enough we were one in our visions even to the city.

Gesammelte Schriften, vol. 1, pp.84-85.
Cited in: Lippman, Edward (1999) The Philosophy & Aesthetics of Music. Lincoln: University of Nebraska Press, p. 163.