“For the theory-practice iteration to work, the scientist must be, as it were, mentally ambidextrous; fascinated equally on the one hand by possible meanings, theories, and tentative models to be induced from data and the practical reality of the real world, and on the other with the factual implications deducible from tentative theories, models and hypotheses.”
Source: Science and Statistics (1976), p. 792
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George E. P. Box 14
British statistician 1919–2013Related quotes
“One test of good theory is that it have practical implications.”
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.

1970s-1980s, "Rationality of Self and Others in an Economic System", 1986

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.

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

"Is the Economic Crisis a Crisis for Economics?", Slate (Nov. 13, 1998)

Internet Encyclopedia of Philosophy
Context: Conceptual expressions are tentative and provisional... [because] the intellectual account... are constructed theories of experience. [And he cautions us to] distinguish between the immediate experience or intuition which might conceivably be infallible and the interpretation which is mixed up with it.