Theory vs Practice I

"Time is that wherein there is opportunity, and opportunity is that wherein there is no great time. Healing is a matter of time, but it is sometimes also a matter of opportunity. However, knowing this, one must attend to medical practice not primarily to plausible theories, but to experience combined with reason. For a theory is a composite memory of things apprehended with sense perception." (Hippocrates of Kos, "Precepts", cca. 4th century)

"Practical sciences proceed by building up; theoretical sciences by resolving into components." (St. Thomas Aquinas, "Sententia libri Ethicorum" [Commentary on the Nicomachean Ethics], 1271)

"Philosophers conceive of the passions which harass us as vices into which men fall by their own fault, and, therefore, generally deride, bewail, or blame them, or execrate them, if they wish to seem unusually pious. And so they think they are doing something wonderful, and reaching the pinnacle of learning, when they are clever enough to bestow manifold praise on such human nature, as is nowhere to be found, and to make verbal attacks on that which, in fact, exists. For they conceive of men, not as they are, but as they themselves would like them to be. Whence it has come to pass that, instead of ethics, they have generally written satire, and that they have never conceived a theory of politics, which could be turned to use, but such as might be taken for a chimera, or might have been formed in Utopia, or in that golden age of the poets when, to be sure, there was least need of it. Accordingly, as in all sciences, which have a useful application, so especially in that of politics, theory is supposed to be at variance with practice; and no men are esteemed less fit to direct public affairs than theorists or philosophers." (Baruch Spinoza, "Political Treatise", 1677)

"In geometry, as in most sciences, it is very rare that an isolated proposition is of immediate utility. But the theories most powerful in practice are formed of propositions which curiosity alone brought to light, and which long remained useless without its being able to divine in what way they should one day cease to be so. In this sense it may be said, that in real science, no theory, no research, is in effect useless." (Voltaire, "A Philosophical Dictionary", 1764)

"The world can doubtless never be well known by theory: practice is absolutely necessary; but surely it is of great use to a young man, before he sets out for that country, full of mazes, windings, and turnings, to have at least a general map of it, made by some experienced traveler." (Philip Stanhope, "Letters Written by the Earl of Chesterfield to His Son", 1827)

"Discrepancy between theory and practice, which in sound physical and mechanical science is a delusion, has a real existence in the minds of men; and that fallacy, through rejected by their judgments, continues to exert and influence over their acts." (William J M Rankine, "On the Harmony of Theory and Practice in Mechanics", 1856)

"Mechanical knowledge may [...] be distinguished into three kinds; purely scientific knowledge, purely practical knowledge, and that intermediate kind of knowledge which relates to the application of scientific principles to practical purposes, and which arises from understanding the harmony of theory and practice." (William J M Rankine, "On the Harmony of Theory and Practice in Mechanics", 1856)

"Some of the evils which are caused by the fallacy of an incompatibility between theory and practice having been described, it must now be admitted, that at the present time those evils show a decided tendency to decline." (William J M Rankine, "On the Harmony of Theory and Practice in Mechanics", 1856)

"Isolated facts and experiments have in themselves no value, however great their number may be. They only become valuable in a theoretical or practical point of view when they make us acquainted with the law of a series of uniformly recurring phenomena, or, it may be, only give a negative result showing an incompleteness in our knowledge of such a law, till then held to be perfect." (Hermann von Helmholtz, "The Aim and Progress of Physical Science", 1869)