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.
- 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.
- 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.
- 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.
- Great theories are expansive; failures mire us in dogmatism and tunnel vision.
- Stephen Jay Gould, Eight Little Piggies (1993), "More Light on Leaves".
- 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.
- 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.
- Friedrich Hayek (1948) Individualism and Economic Order
- 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.
- 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 (1843) Contribution to the Critique of Hegel's Philosophy of Right
- 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