“In short, the success of macroeconomic activism, in both theory and practice, has made it possible for free market microeconomics to survive--again both in theory and in practice.”

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

Source: The Last Vampire

Source: Fifty years of information progress (1994), p. 7: Introduction.

On Practice (1937)

Source: Science and Statistics (1976), p. 792

Michel Henry, Marx I. une philosophie de la réalité, éd. Gallimard, coll. « Nrf », 1976, p. 353
Books on Economy and Politics, Marx. A Philosophy of Human Being (1976)
Original: (fr) Parce que la pratique est subjective, la théorie qui est toujours la théorie d’un objet, ne peut atteindre la réalité de cette pratique, ce qu’elle est en elle-même, sa subjectivité précisément, mais seulement se la représenter, de telle manière que cette représentation laisse hors d’elle l’être réel de la pratique, l’effectivité du faire. La théorie ne fait rien.

Message to Linux kernel mailing list, 2009-03-25, Torvalds, Linus, 2009-03-25 http://lkml.org/lkml/2009/3/25/632,
2000s, 2009

Review of Arthur Koestler’s The Act of Creation, in the New Statesman, 19 June 1964
1960s