^L. A. Zadeh, "The concept of a linguistic variable and its application to approximate reasoning" Information Sciences, Volume 8, Issue 3, 1975, Pages 199-249
^Fuzzy Logic for Business and Industry Earl Cox, Charles River Media, pp188,214,302,306,352 1995 ISBN1-886801-01-0
^The Fuzzy Systems Handbook, Second Edition Earl Cox, Academic Press, 1999 ISBN0-12-194455-7 Ch 6 Fuzzy Reasoning, § 1 The Role of Linguistic Variables
^On the Modeling of Linguistic Information using Random Sets Hung T. Nguyen p. 242 in Readings in Fuzzy Sets for Intelligent Systems. Morgan Kaufmann 1993. Dubois, Prade, and Yager eds.
^Joseph GoguenFuzzy Sets And The Social Nature of Truth in Advances in Fuzzy Sets and Systems, North Holland, 1979. § 2.3 Linguistic Truth Values. ISBN0-444-85372-3