„In theory there is no difference between theory and practice; in practice there is.“

—  Yogi Berra

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

Last update May 22, 2020. History
Yogi Berra photo
Yogi Berra57
American baseball player, manager, coach 1925 - 2015

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„In theory, there is no difference between theory and practice. But, in practice, there is.“

—  Jan L. A. van de Snepscheut Dutch computer scientist 1953 - 1994

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

Paul Krugman photo
Roland Barthes photo

„The theory of the Text can coincide only with a practice of writing.“

—  Roland Barthes French philosopher, critic and literary theorist 1915 - 1980

Conclusion
From Work to Text (1971)
Context: The discourse on the Text should itself be nothing other than text, research, textual activity, since the Text is that social space which leaves no language safe, outside, nor any subject of the enunciation in position as judge, master, analyst, confessor, decoder. The theory of the Text can coincide only with a practice of writing.

„One test of good theory is that it have practical implications.“

—  Charles Perrow American sociologist 1925 - 2019

Source: 1970s, Organizational Analysis: A Sociological View, 1970, p. vii
Context: It is surprising how much discipline is imposed upon theory by requiring that it ‘make a difference’ and provide guidance or useful illumination. I learned long ago from students in professional schools that questions of ‘so what’ or ‘what relevance does this have’ do not signify impatience with theory per se, much less anti-intellectualism, but only impatience with the obvious, general, remote, and vague statements that often parade as social science theory. One test of good theory is that it have practical implications.

Stéphane Dion photo

„Canada is a country that works better in practice than in theory.“

—  Stéphane Dion Canadian politician 1955

As quoted in "One nation or many?" https://web-beta.archive.org/web/20170522044424/http://www.economist.com/node/8173164 (16 November 2006), The Economist

„Because practice is subjective, theory which is always the theory of an object, can't access to the reality of this practice, what it is in itself, but only represent it, in such a way that this representation lets out of itself the real being of practice, the effectivity of the doing. Theory does nothing.“

—  Michel Henry French writer 1922 - 2002

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.

Anthony Trollope photo
Fausto Cercignani photo

„If you refuse to take account of theory, then you have forgotten that practice is often an offspring of theory.“

—  Fausto Cercignani Italian scholar, essayist and poet 1941

Examples of self-translation (c. 2004), Quotes - Zitate - Citations - Citazioni

Mao Zedong photo
John William Dunne photo

„There is as yet no unified theory of retrieval systems, and a good deal of retrieval practice is still an empirical art, unsullied by theory.“

—  Brian Campbell Vickery British information theorist 1918 - 2009

Preface (1961) p. vi; Partly cited by Stephen E. Robertson (2011) " On retrieval system theory http://www.iskouk.org/conf2011/papers/robertson.pdf".
On Retrieval System Theory (1961)

Linus Torvalds photo

„Theory and practice sometimes clash. And when that happens, theory loses. Every single time.“

—  Linus Torvalds Finnish-American software engineer and hacker 1969

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

„Only yesterday the practical things of today were decried as impractical, and the theories which will be practical tomorrow will always be branded as valueless games by the practical man of today.“

—  William Feller Croatian-American mathematician 1906 - 1970

Introduction, The Nature of Probability Theory, p. 6.
An Introduction To Probability Theory And Its Applications (Third Edition)

Mao Zedong photo
George E. P. Box photo
James Van Allen photo

„All this is very good in theory, but in practice, you take a piece of iron, wind a wire around it, then plug the wire in. The core gets hot, the wires smoke, and the fuse blows. So you see, there are practical limitations to theory.“

—  James Van Allen American nuclear physicist 1914 - 2006

Comments to an undergraduate physics class about transformers, Reach Into Space http://www.time.com/time/magazine/article/0,9171,892531,00.html, Time, 1959-05-04.

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Napoleon I of France photo
Jeremy Hardy photo

„Capitalism is a great idea in theory, but in practice it just doesn't work.“

—  Jeremy Hardy British comedian 1961 - 2019

The News Quiz, BBC Radio 4, November 2008

Alexander Suvorov photo

„No battle can be won in the study, and theory without practice is dead.“

—  Alexander Suvorov Russian military commander 1730 - 1800

Quoted in K. Ossipov, "Suvorov", 1945.

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