Pages 22–23.
"The Scope and Method of Political Economy in the Light of the 'Marginal' Theory of Value and Distribution" (1914), §II
Context: Social reformers and legislators will never be economists, and they will always work on economic theory of one kind or another. They will quote and apply such dicta as they can assimilate, and such acknowledged principles as seem to serve their turn. Let us suppose there were a recognised body of economic doctrine the truth and relevancy of which perpetually revealed itself to all who looked below the surface, which taught men what to expect and how to analyse their experience; which insisted at every turn on the illuminating relation between our conduct in life and our conduct in business; which drove the analysis of our daily administration of our individual resources deeper, and thereby dissipated the mist that hangs about our economic relations, and concentrated attention upon the uniting and all-penetrating principles of our study. Economics might even then be no more than a feeble barrier against passion, and might afford but a feeble light to guide honest enthusiasm, but it would exert a steady and a cumulative pressure, making for the truth. While the experts worked on severer methods than ever, popularisers would be found to drive homely illustrations and analogies into the general consciousness; and the roughly understood dicta bandied about in the name of Political Economy would at any rate stand in some relation to truth and to experience, instead of being, as they too often are at present, a mere armoury of consecrated paradoxes that cannot be understood because they are not true, that every one uses as weapons while no one grasps them as principles.
“Economists can never be free of from difficulties unless they will distinguish between a theory and the application of a theory.”
Source: The Theory of Political Economy (1871), Chapter IV, Theory of Exchange, p. 108.
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William Stanley Jevons 69
English economist and logician 1835–1882Related quotes
"On the Harmony of Theory and Practice in Mechanics" (Jan. 3, 1856)
Source: John Maynard Keynes: 1883-1946: Economist, Philosopher, Statesman (2003), Ch. 27. Portraits of an Unusual Economist
“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
Methods of Mathematics Applied to Calculus, Probability, and Statistics (1985)
Context: When a theory is sufficiently general to cover many fields of application, it acquires some "truth" from each of them. Thus... a positive value for generalization in mathematics.
Source: The Moral Judgment of the Child (1932), Ch. 1 : The Rules of the Game
Context: From the point of view of the practice or application of rules four successive stages can be distinguished.
A first stage of a purely motor and individual character, during which the child handles the marbles at the dictation of his desires and motor habits. This leads to the formation of more or less ritualized schemas, but since play is still purely individual, one can only talk of motor rules and not of truly collective rules.
The second may be called egocentric for the following reasons. This stage begins at the moment when the child receives from outside the example of codified rules, that is to say, some time between the ages of two and five. But though the child imitates this example, he continues to play either by himself without bothering to find play-fellows, or with others, but without trying to win, and therefore without attempting to unify the different ways of playing. In other words, children of this stage, even when they are playing together, play each one "on his own " (everyone can win at once) and without regard for any codification of rules. This dual character, combining imitation of others with a purely individual use of the examples received, we have designated by the term Egocentrism.
A third stage appears between 7 and 8, which we shall call the stage of incipient cooperation. Each player now tries to win, and all, therefore, begin to concern themselves with the question of mutual control and of unification of the rules. But while a certain agreement may be reached in the course of one game, ideas about the rules in general are still rather vague. In other words, children of 7-8, who belong to the same class at school and are therefore constantly playing with each other, give, when they are questioned separately, disparate and often entirely contradictory accounts of the rules observed in playing marbles.
Finally, between the years of 11 and 12, appears a fourth stage, which is that of the codification of rules. Not only is every detail of procedure in the game fixed, but the actual code of rules to be observed is known to the whole society. There is remarkable concordance in the information given by children of 10-12 belonging to the same class at school, when they are questioned on the rules of the game and their possible variations.
1940s, "Autobiographical Notes" (1949)
Context: A theory is the more impressive the greater the simplicity of its premises is, the more different kinds of things it relates, and the more extended is its area of applicability. Therefore the deep impression which classical thermodynamics made upon me. It is the only physical theory of universal content concerning which I am convinced that, within the framework of the applicability of its basic concepts, it will never be overthrown (for the special attention of those who are skeptics on principle).
Source: A Brief History of Time (1988), Ch. 1
Context: Any physical theory is always provisional, in the sense that it is only a hypothesis: you can never prove it. No matter how many times the results of experiments agree with some theory, you can never be sure that the next time the result will not contradict the theory. On the other hand, you can disprove a theory by finding even a single observation that disagrees with the predictions of the theory. As philosopher of science Karl Popper has emphasized, a good theory is characterized by the fact that it makes a number of predictions that could in principle be disproved or falsified by observation. Each time new experiments are observed to agree with the predictions the theory survives, and our confidence in it is increased; but if ever a new observation is found to disagree, we have to abandon or modify the theory.