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In conclusion, a word about your tired expression that there is a difference between theory and praxis. ... Thereby you want to say that praxis should be an unencumbered as possible by theory. Coming from you, this wish is quite intelligible. What you mean by praxis is private profit; what I mean by theory is justice. ~ Karl Barth

Theory is a contemplative and rational type of abstract or generalizing thinking, or the results of such thinking. Depending on the context, the results might for example include generalized explanations of how nature works, or even how divine or metaphysical matters are thought to work.


Quotes are arranged in chronological order

Antiquity through eighteenth century[edit]

  • All men suppose what is called Wisdom to deal with the first causes and the principles of things; so that, as has been said before, the man of experience is thought to be wiser than the possessors of any sense-perception whatever, the artist wiser than the men of experience, the masterworker than the mechanic, and the theoretical kinds of knowledge to be more of the nature of Wisdom than the productive.
    • Aristotle, Metaphysics, 982a1, Complete Works, vol. 2, p. 1553
  • Practical life is not necessarily directed toward other people, as some think; and it is not the case that practical thoughts are only those which result from action for the sake of what ensues. On the contrary, much more practical are those mental activities and reflections which have their goal in themselves and take place for their own sake.
  • Never call yourself a philosopher, nor talk a great deal among the unlearned about theorems, but act conformably to them.
  • A light was kindled amongst the investigators of nature when Galilei let balls of a definite weight roll down the inclined plane. For they saw that they only understand what is produced according to a predetermined plan or hypothesis... for otherwise planless observations made according to no ideas could never be brought into the form of a law which reason demands and seeks. ...Thus physics was brought into the position of a certain science after groping about blindly for so many hundred years.

19th century[edit]

in chronological order
  • Theories usually result from the precipitate reasoning of an impatient mind which would like to be rid of phenomena and replace them with images, concepts, indeed often with mere words.
  • All competent thinkers agree with Bacon that there can be no real knowledge except that which rests upon observed facts. This fundamental maxim is evidently indisputable if it is applied, as it ought to be, to the mature state of our intelligence. But, if we consider the origin of our knowledge, it is no less certain that the primitive human mind could not, and indeed ought not to, have thought in that way. For if, on the one hand, every Positive theory must necessarily be founded upon observations, it is, on the other hand, no less true that, in order to observe, our mind has need of some theory or other. If in contemplating phenomena we did not immediately connect them with principles, not only would it be impossible for us to combine these isolated observations, and therefore to derive profit from them, but we should even be entirely incapable of remembering facts, which would for the most remain unnoted by us.
    Thus there were two difficulties be overcome: the human mind had to observe in order to form real theories, and yet had to form theories of some sort before it could apply itself to a connected series of observations. The primitive human mind, therefore, found itself involved in a vicious circle, from which it would never have had any means of escaping, if a natural way of the difficulty had not fortunately found by the spontaneous development of Theological conceptions. ...chimerical hopes ..exaggerated ideas of man's importance in the universe to which the Theological Philosophy the commencement, ...afforded an indispensable stimulus without the aid which we cannot, indeed, conceive how the primitive human mind would have been induced to undertake any arduous labours.
    • Auguste Comte, Cours de Philosophie Positive (1830-1842); The Positive Philosophy of Auguste Comte (1853) Tr. Harriet Martineau; The Fundamental Principles of the Positive Philosophy: Being the First Two Chapters of the Cours de Philosophie Positive of Auguste Comte (1905) pp. 23-25.
  • It is clear that the arm of criticism cannot replace the criticism of arms. Material force can only be overthrown by material force, but theory itself becomes a material force when it has seized the masses. Theory is capable of seizing the masses when it demonstrates ad hominem, and it demonstrates ad hominem as soon as it becomes radical. To be radical is to grasp things by the root. But for man the root is man himself. What proves beyond doubt the radicalism of German theory, and thus its practical energy, is that it begins from the resolute positive abolition of religion. The criticism of religion ends with the doctrine that man is the supreme being for man. It ends, therefore, with the categorical imperative to overthrow all those conditions in which man is an abased, enslaved, abandoned, contemptible being—conditions which can hardly be better described than in the exclamation of a Frenchman on the occasion of a proposed tax upon dogs: 'Wretched dogs! They want to treat you like men!'
    • Karl Marx, Contribution to the Critique of Hegel's Philosophy of Right (1843)
  • About thirty years ago there was much talk that geologists ought only to observe and not theorise; and I well remember some one saying that at this rate a man might as well go into a gravel-pit and count the pebbles and describe the colours. How odd it is that anyone should not see that all observation must be for or against some view if it is to be of any service!
    • Charles Darwin, Letter to Henry Fawcett (Sept. 18, 1861) in Life of Henry Fawcett (1885) pp. 100-101, and in More Letters of Charles Darwin: a Record of his Work in a Series of hitherto Unpublished Letters (1903) Vol. 1, p. 195, ed., Sir Francis Darwin, Albert Charles Seward.
  • Philosophical theories or ideas, as points of view, instruments of criticism, may help us to gather up what might otherwise pass unregarded by us. “Philosophy is the microscope of thought.” The theory or idea or system which requires of us the sacrifice of any part of this experience, in consideration of some interest into which we cannot enter, or some abstract theory we have not identified with ourselves, or what is only conventional, has no real claim upon us.
  • Their ideas seemed to him fruitful when he was reading or was himself seeking arguments to refute other theories, especially those of the materialists; but as soon as he began to read or sought for himself a solution of problems, the same thing always happened. As long as he followed the fixed definition of obscure words such as spirit, will, freedom, essence, purposely letting himself go into the snare of words the philosophers set for him, he seemed to comprehend something. But he had only to forget the artificial train of reasoning, and to turn from life itself to what had satisfied him while thinking in accordance with the fixed definitions, and all this artificial edifice fell to pieces at once like a house of cards, and it became clear that the edifice had been built up out of those transposed words, apart from anything in life.
    • Leo Tolstoy, Anna Karenina (1873-1877), Tr. C. Garnett (New York: 2003), Part 8, Chapter 9, p. 728
  • And don't all the theories of philosophy do the same, trying by the path of thought, which is strange and not natural to man, to bring him to a knowledge of what he has known long ago, and knows so certainly that he could not live at all without it? Isn't it distinctly to be seen in the development of each philosopher's theory, that he knows what is the chief significance of life beforehand, just as positively as the peasant Fyodor, and not a bit more clearly than he, and is simply trying by a dubious intellectual path to come back to what everyone knows?
    • Leo Tolstoy, Anna Karenina (1873-1877), Tr. C. Garnett (New York: 2003), Part 8, Chapter 13, p. 737
  • It is a condition which confronts us — not a theory.
    • Grover Cleveland, third annual message to Congress (December 6, 1887); reported in George F. Parker, ed., The Writings and Speeches of Grover Cleveland (1892), p. 86. Cleveland was referring to the tariff.
  • During all those years of experimentation and research, I never once made a discovery. All my work was deductive, and the results I achieved were those of invention, pure and simple. I would construct a theory and work on its lines until I found it was untenable. Then it would be discarded at once and another theory evolved. This was the only possible way for me to work out the problem. … I speak without exaggeration when I say that I have constructed 3,000 different theories in connection with the electric light, each one of them reasonable and apparently likely to be true. Yet only in two cases did my experiments prove the truth of my theory. My chief difficulty was in constructing the carbon filament. . . . Every quarter of the globe was ransacked by my agents, and all sorts of the queerest materials used, until finally the shred of bamboo, now utilized by us, was settled upon.
    • Thomas Edison on his years of research in developing the electric light bulb, as quoted in "Talks with Edison" by George Parsons Arthropod in Harper magazine, Vol. 80 (February 1890), p. 425.
  • [T]he studies preliminary to the construction of a great theory should be at least as deliberate and thorough as those that are preliminary to the building of a dwelling-house.
    • Charles Sanders Pierce, "The Architecture of Theories" in The Monist (January 1891) Vol. I, No. 2, p. 161ff.
  • [W]ith regard to light, that it consists of vibrations was almost proved by the phenomena of diffraction, while those of polarisation showed the excursions of the particles to be perpendicular to the line of propogation; but the phenomena of dispersion, etc., require additional hypotheses which may be very complicated. Thus, the further progress of molecular speculation appears quite uncertain. If hypotheses are to be tried haphazard, or simply because they will suit certain phenomena, it will occupy the mathematical physicists of the world say half a century on the average to bring each theory to the test, and since the number of possible theories may go up into the trillion, only one of which can be true, we have little prospect of making further solid additions to the subject in our time.
    • Charles Sanders Pierce, "The Architecture of Theories" in The Monist (January 1891) Vol. I, No. 2, p. 161ff.

20th century, first part[edit]

  • We sometimes speak of stubborn facts. Nonsense! A fact is a mere babe when compared with a stubborn theory.
  • In conclusion, a word about your tired expression that there is a difference between theory and praxis. ... Thereby you want to say that praxis should be an unencumbered as possible by theory. Coming from you, this wish is quite intelligible. What you mean by praxis is private profit; what I mean by theory is justice.
    • Karl Barth, "Jesus Christ and the Movement for Social Justice" (1911), in Karl Barth and Radical Politics (Westminster Press: 1976), p. 45
  • There is no great harm in the theorist who makes up a new theory to fit a new event. But the theorist who starts with a false theory and then sees everything as making it come true is the most dangerous enemy of human reason.
  • Things and events explain themselves, and the business of thought is to brush aside the verbal and conceptual impediments which prevent them from doing so. Start with the notion that it is you who explain the Object, and not the Object that explains itself, and you are bound to end in explaining it away. It ceases to exist, its place being taken by a parcel of concepts, a string of symbols, a form of words, and you find yourself contemplating, not the thing, but your theory of the thing.
  • I firmly believe people have hitherto been a great deal too much taken up about doctrine and far too little about practice. The word doctrine, as used in the Bible, means teaching of duty, not theory. I preached a sermon about this. We are far too anxious to be definite and to have finished, well-polished, sharp-edged systems — forgetting that the more perfect a theory about the infinite, the surer it is to be wrong, the more impossible it is to be right.
    • George MacDonald, in a letter to his father, quoted in George MacDonald and His Wife (1924) by Greville MacDonald
  • Conservatives feel instinctively that it is new ideas more than anything else that cause change. But, from its point of view rightly, conservatism fears new ideas because it has no distinctive principles of its own to oppose them; and, by its distrust of theory and its lack of imagination concerning anything except that which experience has already proved, it deprives itself of the weapons needed in the struggle of ideas. Unlike liberalism, with its fundamental belief in the long-range power of ideas, conservatism is bound by the stock of ideas inherited at a given time. And since it does not really believe in the power of argument, its last resort is generally a claim to superior wisdom, based on some self-arrogated superior quality.

20th century, second part[edit]

  • The final test of a theory is its capacity to solve the problems which originated it.
    • George Dantzig (1963) Linear Programming and Extensions, Princeton University Press, p. vii.
  • There may thus well exist better "scientific" evidence for a false theory, which will be accepted because it is more "scientific", than for a valid explanation, which is rejected because there is no sufficient quantitative evidence for it.
  • No single theory ever agrees with all the facts in its domain.
  • How can we possibly test, or improve upon the truth of a theory if it is built in such a manner then any conceivable event can be described, and explained, in terms of its principles? The only way of investigating such all-embracing principles would be to compare them with a different set of equally all embracing principles- but this procedure has been excluded from the very beginning.
  • Experience arises together with theoretical assumptions not before them, and an experience without theory is just as incomprehensible as is (allegedly) a theory without experience.
  • Not only are facts and theories in constant disharmony, they are never as neatly separated as everyone makes them out to be.
  • Facts and theories are different things, not rungs in a hierarchy of increasing certainty. Facts are the world's data. Theories are structures of ideas that explain and interpret facts. Facts do not go away while scientists debate rival theories for explaining them.
    • Stephen Jay Gould "Evolution as Fact and Theory", pp. 254–55, originally appeared in Discover Magazine, May 1981.
  • Great theories are expansive; failures mire us in dogmatism and tunnel vision.
  • During the period that began with classical Greece and ended with late pagan antiquity, philosophy was more than merely a theoretical discipline. Even when Aristotle identified philosophy with "theory," his purpose is to argue ... that a life of theoretical activity, the life of philosophy, was the best life that human beings could lead.

21th century[edit]

  • In theory, there is no difference between theory and practice. But, in practice, there is.
    • Attributed to Jan L. A. van de Snepscheut in: Doug Rosenberg and Matt Stephens (2007) Use Case Driven Object Modeling with UMLTheory and Practice p. xxvii; Quote is also cited without attribution in Doug Rosenberg and Kendall Scott (2001) Applying Use Case Driven Object Modeling With UML, p. 1
  • The ultimate goal of science is to understand the natural world in terms of scientific theories, which are concepts that join together well-supported and related hypotheses. In ordinary speech, the word theory refers to a speculative idea. In contrast, a scientific theory is supported by a broad range of observations, experiments, and data often from a variety of disciplines.
    • Sylvia S. Mader, Biology (10th ed., 2010), Ch. 1. A View of Life
  • If you refuse to take account of theory, then you have forgotten that practice is often an offspring of theory.
    • Fausto Cercignani in: Brian Morris, Simply Transcribed. Quotations from Writings by Fausto Cercignani, 2014, quote 54.

See also[edit]

External links[edit]

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