irrational
ih-RASH-uh-nuhl
/ɪˈræʃ.ən.əl/
Not logical, reasonable, or consistent with rational economic principles.
In behavioral economics, implies systematic and predictable departures from expected utility theory rather than random madness.
The story behind the word. Derived from the Latin 'ratio', meaning calculation or reason. Ancient Roman mathematicians used 'irrationalis' to describe numbers like the square root of 2 that could not be computed as simple fractions. Behavioral economists later picked up the term to describe choices that defy standard economic math.
Word relationships
- illogical: Illogical means violating rules of formal logic; irrational implies action contrary to reason or self-interest.
- unreasonable: Unreasonable stresses unwillingness to compromise, while irrational emphasizes cognitive inconsistency.
- rational: Rational means strictly conforming to sound reasoning, logic, and self-interest maximization.
- logical: Logical means following rigorous step-by-step deductive consistency.
Commonly confused with
- unreasonable: Unreasonable describes social demands that exceed fair limits, whereas irrational describes thought processes that fail economic logic.
Word family
- irrationality (noun): The quality of lacking logical or consistent economic reasoning.
- irrationally (adverb): In an illogical or self-defeating manner.
Collocations
- irrational exuberance
- irrational behavior
- predictably irrational
- irrational decision
Idioms & expressions
- out of one's mind
- defying logic
Example sentences
- "The stock bubble was driven by irrational exuberance among speculative retail traders." Financial market analysis (Alan Greenspan, Federal Reserve Speech (1996))
- "Consumers exhibit irrational choices when they value avoiding losses far more than achieving equal gains." Behavioral economics publication
Memory hook
IRRATIONAL combines IR (not) + RATIONAL (logical). Not calculated logically. Irrational = Defying logical calculation.
When not to use
Avoid using as a casual insult for someone with whom you simply disagree politcally.
Fun facts
- Dan Ariely named his bestselling book 'Predictably Irrational' because human errors aren't random—we repeat the exact same mental mistakes over and over.
Explore more words
Rationality, surreal, rationalize, anomaly, compulsive, eccentric
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