“One seeking to understand the recurrent ebb and flow of economic activity characteristic of the present day finds these numerous explanations both suggestive and perplexing. All are plausible, but which is valid? None necessarily excludes all the others, but which is the most important? Each may account for certain phenomena; does any one account for all the phenomena? Or can these rival explanations be combined in such a fashion as to make a consistent theory which is wholly adequate?
There is slight hope of getting answers to these questions by a logical process of proving and criticizing the theories. For whatever merits of ingenuity and consistency they may possess, these theories have slight value except as they give keener insight into the phenomena of business cycles. It is by study of the facts which they purport to interpret that the theories must be tested. But the perspective of the investigation would be distorted if we set out to test each theory in turn by collecting evidence to confirm or to refute it. For the point of interest is not the validity of any writer's views, but clear comprehension of the facts. To observe, analyze, and systematize the phenomena of prosperity, crisis, and depression is the chief task. And there is better prospect of rendering service if we attack this task directly, than if we take the round about way of considering the phenomena with reference to the theories.
This plan of attacking the facts directly by no means precludes free use of the results achieved by others. On the contrary, their conclusions suggest certain facts to be looked for, certain analyses to be made, certain arrangements to be tried. Indeed, the whole investigation would be crude and superficial if we did not seek help from all quarters. But the help wanted is help in making a fresh examination into the facts.”

Chpt.2, p. 21
Principles of Geology (1832), Vol. 1
Context: But Strabo rejects this theory as insufficient to account for all the phenomena, and he proposes one of his own, the profoundness of which modern geologists are only beginning to appreciate. 'It is not,' he says, 'because the lands covered by seas were originally at different altitudes, that the waters have risen, or subsided, or receded from some parts and inundated others. But the reason is, that the same land is sometimes raised up and sometimes depressed, and the sea also is simultaneously raised and depressed, so that it either overflows or returns into its own place again. We must therefore ascribe the cause to the ground, either to that ground which is under the sea, or to that which becomes flooded by it, but rather to that which lies beneath the sea, for this is more moveable, and, on account of its humidity, can be altered with great celerity. It is proper,' he observes in continuation, 'to derive our explanations from things which are obvious, and in some measure of daily occurrence, such as deluges, earthquakes, volcanic eruptions, and sudden swellings of the land beneath the sea;' for the last raise up the sea also, and when the same lands subside again, they occasion the sea to be let down. And it is not merely the small, but the large islands also, and not merely the islands, but the continents, which can be lifted up together with the sea; and both large and small tracts may subside, for habitations and cities, like Bure, Bizona, and many others, have been engulfed by earthquakes.

Source: The Fabric of Reality (1997), Ch. 13; commentary on the ideas of Thomas Kuhn, as presented in the book The Structure of Scientific Revolutions

[John Clarke Slater, Nathaniel Herman Frank, Electromagnetism, Courier Dover Publications, 1969, 0486622630, 11]

Source: Speech http://hansard.millbanksystems.com/commons/1871/jul/28/parliament-order-of-business in the House of Commons (28 July 1871).

Source: War and peace (2005), p. 3

Aphorism 39.
Philosophy of the Inductive Sciences (1840)

Philosophy in the Twentieth Century (1982) p. 133.

"The Use of Models: Experience," 1969

Source: Nationalism and Culture (1937), Ch. 1 "The Insufficiency of Economic Materialism"
Context: No thinking man in this day can fail to recognise that one cannot properly evaluate an historical period without considering economic conditions. But much more one-sided is the view which maintains that all history is merely the result of economic conditions, under whose influence all other life phenomena have received form and imprint.
There are thousands of events in history which cannot be explained by purely economic reasons, or by them alone. It is quite possible to bring everything within the terms of a definite scheme, but the result is usually not worth the effort. There is scarcely an historical event to whose shaping economic causes have not contributed, but economic forces are not the only motive powers which have set everything else in motion. All social phenomena are the result of a series of various causes, in most cases so inwardly related that it is quite impossible clearly to separate one from the other. We are always dealing with the interplay of various causes which, as a rule, can be clearly recognised but cannot be calculated according to scientific methods.