What does irrationality mean?
Irrationality is the quality of being unreasonable, illogical, or guided by emotion rather than careful thought. The word is used for conduct and decisions that disregard evidence, sound judgment, or logical consequences, as well as for more specific instances of such behavior. It is usually a formal and somewhat critical term, though writers may use it neutrally when discussing the broader human tendency to act irrationally. In discussions of psychology, philosophy, economics, and everyday relationships, irrationality often contrasts with rationality and reason. The word is particularly useful when describing not merely an incorrect opinion, but a pattern of thought or action that appears disconnected from coherent reasoning. Its use can range from academic analysis to commentary on ordinary disputes and impulsive decisions.
nounThe quality or state of being irrational, especially of behavior or thinking that is not based on reason, logic, or sound judgment. It can also refer to an instance of such unreasonable conduct.
- The quality of thinking or behaving without adequate reason, logic, or sound judgment.
- An instance of unreasonable or illogically motivated thought or conduct.
"The debate exposed the irrationality of allowing emotion to determine every decision."
"The irrationality of the rumor was obvious once the original source was checked."
"She tried to understand her colleague's irrationality without allowing it to affect the project."
The plural is uncommon; the singular is normally used for the general condition or quality.
"The novel explores the irrationalities that shape public life."
Irrationality is the human tendency to let emotion, habit, or impulse override reason—even when the evidence is clear.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does irrationality come from?
The word was formed in the early 19th century from irrational plus the suffix -ity, meaning the condition or quality of being irrational. Irrational itself comes from Latin irrationalis, meaning “not rational” or “without reason,” built from in-, a prefix expressing negation, and ratio, “reason” or “reasoning.” The related English word rational has the same Latin foundation, while rationality and irrationally reflect the same contrast between reason and its absence.
How irrationality is actually used
Usually formal and potentially critical. It often describes conduct, decisions, beliefs, or arguments that depart from reason or sound judgment; in some contexts, it may sound strongly disapproving.