[rash-uh-nl-ahyz, rash-nl-ahyz]

verb (used with object), ra·tion·al·ized, ra·tion·al·iz·ing.

verb (used without object), ra·tion·al·ized, ra·tion·al·iz·ing.

to invent plausible explanations for acts, opinions, etc., that are actually based on other causes: He tried to prove that he was not at fault, but he was obviously rationalizing.
to employ reason; think in a rational or rationalistic manner.

Also especially British, ra·tion·al·ise.

Origin of rationalize

First recorded in 1810–20; rational + -ize
Related formsra·tion·al·i·za·tion, nounra·tion·al·iz·er, nounnon·ra·tion·al·i·za·tion, nounnon·ra·tion·al·ized, adjectiveo·ver·ra·tion·al·i·za·tion, nouno·ver·ra·tion·al·ize, verb, o·ver·ra·tion·al·ized, o·ver·ra·tion·al·iz·ing.sem·i·ra·tion·al·ized, adjectiveun·ra·tion·al·ized, adjectiveun·ra·tion·al·iz·ing, adjective

Usage note

Although rationalize retains its principal 19th-century senses “to make conformable to reason” and “to treat in a rational manner,” 20th-century psychology has given it the now more common meaning “to ascribe (one's acts, opinions, etc.) to causes that seem reasonable but actually are unrelated to the true, possibly unconscious causes.” Although the possibility of ambiguity exists, the context will usually make clear which sense is intended.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for rationalise

Historical Examples of rationalise

  • Her mother attempted to rationalise and formulate her daughter's position.

    A Likely Story

    William De Morgan

  • She was resolved to understand herself, to rationalise her overthrow.

    Mount Music

    E. Oe. Somerville and Martin Ross

  • The attempt to rationalise the narrative of Scripture was no new one.

  • Our traditions will buttress and rationalise the instinct to power until we see that it is mischievous.

  • The more popular method, therefore, at the present day is not to rationalise, but to try to outsceptic the sceptic.

British Dictionary definitions for rationalise




to justify (one's actions, esp discreditable actions, or beliefs) with plausible reasons, esp after the event
psychol to indulge, often unchallenged, in excuses for or explanations of (behaviour about which one feels uncomfortable or guilty)
to apply logic or reason to (something)
to eliminate unnecessary equipment, personnel, or processes from (a group of businesses, factory, etc), in order to make it more efficient
(tr) maths to eliminate one or more radicals without changing the value of (an expression) or the roots of (an equation)
Derived Formsrationalization or rationalisation, nounrationalizer or rationaliser, noun
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for rationalise

chiefly British English spelling of rationalize. For suffix, see -ize. Related: Rationalised; rationalising; rationalisation.


chiefly British English spelling of rationalize; see -ize. Related: Rationalised; rationalising; rationalisation.



1767, "explain in a rational way, make conformable to reason," from rational + -ize. In the psychological sense of "to give an explanation that conceals true motives" it dates from 1922. Related: Rationalized; rationalizing.

Online Etymology Dictionary, © 2010 Douglas Harper

rationalise in Medicine




To make rational.
To devise self-satisfying but false or inconsistent reasons for one's behavior, especially as an unconscious defense mechanism through which irrational acts or feelings are made to appear rational to oneself.
Related formsra′tion•al•i•zation (-lĭ-zāshən) n.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.