At the other extreme is a set of parts that are completely unrelated: that is, a change in each part depends only on that part alone. The variation in the set is the physical sum of the variations of the parts. Such behavior is called independent or physical summativity.
Source: Definition of System, 1956, p. 23
“[Lewin formally defines a Gestalt as:] a system whose parts are dynamically connected in such a way that a change of one part results in a change of all other parts.”
Source: 1930s, Principles of topological psychology, 1936, p. 218, as cited in: Granville Stanley Hall, Edward Bradford Titchener, Karl M. Dallenbach (1937) The American journal of psychology. Vol. 50, p. 374.
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Kurt Lewin 48
German-American psychologist 1890–1947Related quotes
Cited in: Harold Chestnut (1967) Systems Engineering Methods. p. 121
A methodology for systems engineering, 1962
Source: Something More, A Consideration of the Vast, Undeveloped Resources of Life (1920), p. 37

Cited in: Haluk Demirkan, James C. Spohrer, Vikas Krishna (2011) The Science of Service Systems. p. 274.
1970s, Towards a System of Systems Concepts, 1971

“Language is a system whose parts can and must all be considered in their synchronic solidarity.”
La langue est un systéme dont toutes les parties peuvent et doivent être considérés dans leur solidarité synchronique.
Source: Cours de linguistique générale (1916), p. 87 (1916, p. 124; Part 1, Ch. 3, sec. 3.)