Source: Break-Out from the Crystal Palace (1974), p. 168
“Economics is a science of thinking in terms of models joined to the art of choosing models which are relevant to the contemporary world. It is compelled to be this, because, unlike the typical natural science, the material to which it is applied is, in too many respects, not homogeneous through time. The object of a model is to segregate the semi-permanent or relatively constant factors from those which are transitory or fluctuating so as to develop a logical way of thinking about the latter, and of understanding the time sequences to which they give rise in particular cases.
Good economists are scarce because the gift for using "vigilant observation" to choose good models, although it does not require a highly specialised intellectual technique, appears to be a very rare one.”
Letter to Roy Harrod (4 July 1938), in The Collected Writings of John Maynard Keynes, Vol. XIV (1971), p. 297
Help us to complete the source, original and additional information
John Maynard Keynes 122
British economist 1883–1946Related quotes
Source: What Is This Thing Called Science? (Third Edition; 1999), Chapter 3, Experiment, p. 27.
Source: Europe and the People Without History, 1982, Chapter 1, Introduction, p. 6.

Discourse no. 12; vol. 2, p. 104.
Discourses on Art

Source: Object-Oriented Software Engineering: A Use Case Driven Approach (1992), p. 42; cited in: Sten Carlsson and Benneth Christiansson. (1999) " The Concept of Object and its Relation to Human Thinking: Some Misunderstandings Concerning the Connection between Object-Orientation and Human Thinking http://www.vits.org/publikationer/dokument/289.pdf." Informatica, Lith. Acad. Sci. 10.2. p. 147-160.

Source: Linear programming and extensions (1963), p. 2
Source: Systems Engineering Tools, (1965), p. 108; As cited in: Alberto Ortiz (1992, p. 13)
Source: MDA Distilled. Principles of Model-Driven Architecture, 2003, p. 36.