“A theorem is a proposition which is a strict logical consequence of certain definitions and other propositions”
Anatol Rapoport. " Various meanings of “theory”." http://www.acsu.buffalo.edu/~fczagare/PSC%20504/Rapoport%20(1958).pdf American Political Science Review 52.04 (1958): 972-988.
1950s
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Anatol Rapoport 45
Russian-born American mathematical psychologist 1911–2007Related quotes

“There are numerous theorems in economics that rely upon mathematically fallacious propositions.”
Source: Debunking Economics - The Naked Emperor Of The Social Sciences (2001), Chapter 12, Don't Shoot Me, I'm Only The Piano, p. 259

A reply to Olbers' 1816 attempt to entice him to work on Fermat's Theorem. As quoted in The World of Mathematics (1956) Edited by J. R. Newman

Principles of Mathematics (1903), Ch. I: Definition of Pure Mathematics, p. 3
1900s

“I cannot get from the nature of the proposition to the individual logical operations!!!”
Journal entries (12 March 1915 and 15 March 1915) p. 41e
1910s, Notebooks 1914-1916
Context: I cannot get from the nature of the proposition to the individual logical operations!!!
That is, I cannot bring out how far the proposition is the picture of the situation. I am almost inclined to give up all my efforts.

“A tautology's truth is certain, a proposition's possible, a contradiction's impossible.”
Certain, possible, impossible: here we have the first indication of the scale that we need in the theory of probability.
4.464
Original German: Die Wahrheit der Tautologie ist gewiss, des Satzes möglich, der Kontradiktion unmöglich
Source: 1920s, Tractatus Logico-Philosophicus (1922)

Source: "Outlines of the Science of Energetics," (1855), p. 121; Second paragraph