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See also: Trilemma



The project management triangle is a trilemma (sense 1): it claims that a project can be completed cheaply and quickly, quickly and well, or well and cheaply, but not all three at once

The word is modelled on dilemma, with di- (prefix meaning ‘two, twice, double’) replaced by tri- (prefix meaning ‘three’).



trilemma (plural trilemmas)

  1. A circumstance in which a choice must be made between three options that seem equally undesirable or, put another way, in which a choice must be made among three desirable options, only two of which are possible at the same time.
    • 1853 March, “Article I. The Mode of Baptism.”, in The True Baptist, volume I, number 3, Jackson, Miss.: Published by the editor, OCLC 1013393781, page 76:
      With all these dilemmas and trilemmas crowding the mind, if one did not know better, one might be tempted to doubt whether any such versions were ever made at all.
    • 2004 March, Maurice Obstfeld; Jay C. Shambaugh; Alan M. Taylor, “The Trilemma in History: Tradeoffs among Exchange Rates, Monetary Policies, and Capital Mobility”, in Econometrics Laboratory, University of California, Berkeley[1], archived from the original on 12 August 2017, page 1:
      At the most general level, policymakers in open economies face a macroeconomic trilemma: 1. to stabilize the exchange rate; 2. to enjoy free international capital mobility; 3. to engage in a monetary policy oriented toward domestic goals. Because only two out of the three objectives can be mutually consistent, policymakers must decide which one to give up.
  2. (logic) An argument containing three alternatives, jointly exhaustive either under any condition(s) or under all condition(s) consistent with the universe of discourse of that argument, that each imply the same conclusion.
    • 1851, [James William Gilbart], Logic for the Million: A Familiar Exposition of the Art of Reasoning, London: Longman, Brown, Green & Longmans, OCLC 38815279, part IV (The Points of Reasoning), section V (Reasoning by Compound Syllogism), subsection III (The Trilemma), page 324:
      It has been remarked as a characteristic of the late Sir Robert Peel, that in introducing his measures to the House of Commons, he often used the trilemma. "Three courses are before us—to go backward, to stand still, to go forward. We cannot go backward; we cannot stand still; we must, then, go forward."
    • 1862 July 1, “Art. VII.—(1.) Kirche und Kirchen, Papstthum und Kirchenstaat. Historisch-politische Bertrachtungen von Joh. Jos. Ign. v. Döllinger. Zweiter unveränderter Abdruck. München: 1861. (2.) The Church and the Churches; or, The Papacy and The Temporal Power. An Historical and Political Review. By Dr. Döllinger. Translated by William Bernard MacCabe. London: 1862.”, in The British Quarterly Review, volume XXXVI, number LXXI, London: Jackson, Walford, & Hodder 18, St. Paul's Churchyard and Simpkin, Marshall and Co., Stationers' Hall Court; Edinburgh: W. Oliphant & Co.; Glasgow: J[ames] MacLehose; Dublin: J. Robertson, OCLC 5773149, page 156:
      And in anticipation of it, while he [Johann Joseph Ignaz von Döllinger] declares at one moment that it would be profane to limit Divine Providence to an alternative, he affirms in the next that there can be no harm whatever in shutting it up to a supposed exhaustive trilemma.

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