“…talent and genius operate outside the rules, and theory conflicts with practice.”

Some Notes on Caravaggio (1956)
Context: Caravaggio speaks to us out of a consciousness that is brooding and obsessive, and affects us in a way that is not simply artistic. By this I mean that he comes close to presenting us with a sensation of amorphous and desperate desire unredeemed by an authoritative vision. It can be felt in the apprehensive boredom of the unsuccessful pictures and in the oppressive intensity of the best. If this sensation were deep enough it might have destructive effects, since we all live within that margin of order which we succeed in imposing on life, i. e., on the unfulfilled longings of the heart, and his work might then be truly diabolic. His genius operates in that world of antithesis where the conflict between ideal and reality rages, and the moral victory, i. e., the ultimate affirmation of the goodness of life, is always so tenuously won that we feel the dread of chaos intensely- even when he is completely successful. If there could be such a contradictory phenomenon as the uninnocent artist he might be it. He indicates the sort of sensations we might expect from such a monster. But since he is wholly innocent beneath the apparent evidence of corruption he ends by moving us in a profound and religious way.

1905 - 1910, Notes of a Painter' (1908)

Attributed to Schumann in: The Atlantic Monthly, Vol. 112, 1913, p. 811

Report on Manufactures (1791)

Bartlett's Familiar Quotations, 10th ed. (1919), Journal

Attributed in Nassim Nicholas Taleb, Antifragile - Things that Gain From Disorder (2012), p. 213.
The earliest known appearance of this quote in print is Walter J. Savitch, Pascal: An Introduction to the Art and Science of Programming (1984), where it is attributed as a "remark overheard at a computer science conference". It circulated as an anonymous saying for more than ten years before attributions to Jan L. A. van de Snepscheut and Yogi Berra began to appear (and later still to various others).
Disputed, Misattributed

The earliest known appearance in print of this quote is Benjamin Brewster in the October 1881 - June 1882 issue of "The Yale Literary Magazine." Brewster asks, "What does his lucid explanation amount to but this, that in theory there is no difference between theory and practice, while in practice there is?" See page 202. https://books.google.com/books?id=iJ9MAAAAMAAJ&printsec=frontcover&vq=%22no+difference%22#v=onepage&q&f=false It has also been attributed by Doug Rosenberg and Matt Stephens (2007) Use Case Driven Object Modeling with UMLTheory and Practice p. xxvii as well as Walter J. Savitch, Pascal: An Introduction to the Art and Science of Programming (1984), where it is attributed as a "remark overheard at a computer science conference". It circulated as an anonymous saying for more than ten years before attributions to van de Snepscheut and Yogi Berra began to appear (and later still to various others).
Misattributed