“The advantages of models are, on one hand, that they force us to present a "complete" theory by which I mean a theory taking into account all relevant phenomena and relations and, on the other hand, the confrontation with observation, that is, reality.”

Source: Science and Statistics (1976), p. 792

Source: General System Theory (1968), 2. The Meaning of General Systems Theory, p. 34

Source: Business Cycles, 1913, p. 19-20; as cited in: Mary S. Morgan. The History of Econometric Ideas. p. 46

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 Tao of Physics (1975), Ch. 10, The Unity of All Things, p. 132.

Source: 1940s-1950s, Administrative Behavior, 1947, p. 43.

Third Annual Message to Congress (6 December 1887), discussing tariffs. Compare "Free trade is not a principle, it is an expedient", Benjamin Disraeli, On Import Duties, April 25, 1843.
Context: Both of the great political parties now represented in the Government have by repeated and authoritative declarations condemned the condition of our laws which permit the collection from the people of unnecessary revenue, and have in the most solemn manner promised its correction; and neither as citizens nor partisans are our countrymen in a mood to condone the deliberate violation of these pledges.
Our progress toward a wise conclusion will not be improved by dwelling upon the theories of protection and free trade. This savors too much of bandying epithets. It is a condition which confronts us — not a theory. Relief from this condition may involve a slight reduction of the advantages which we award our home productions, but the entire withdrawal of such advantages should not be contemplated. The question of free trade is absolutely irrelevant, and the persistent claim made in certain quarters that all the efforts to relieve the people from unjust and unnecessary taxation are schemes of so-called free traders is mischievous and far removed from any consideration for the public good.

Aphorism 39.
Philosophy of the Inductive Sciences (1840)

Paul Samuelson, Tjalling Koopmans, and Richard Stone. "Report of the evaluative committee for Econometrica." Econometrica- journal of the Econometric Society. (1954): 141-146.