irrationality
C1formal
Definition
Meaning
The quality or state of not being based on or governed by reason or logical thinking.
Behavior, actions, beliefs, or decisions that defy logical explanation, often driven by emotion, impulse, prejudice, or mental disturbance. In mathematics, the property of a number (like π or √2) that cannot be expressed as a ratio of two integers.
Linguistics
Semantic Notes
Often used to critique decisions, beliefs, or systems. Carries a negative evaluation when applied to human behavior, implying a failure of rationality. The mathematical sense is purely technical and neutral.
Dialectal Variation
British vs American Usage
Differences
No significant difference in meaning or usage. Spelling is consistent.
Connotations
Identical connotations in both varieties.
Frequency
Slightly more frequent in UK academic/philosophical writing, but the difference is marginal.
Vocabulary
Collocations
Grammar
Valency Patterns
the irrationality of [noun phrase][verb] irrationalityirrationality [preposition] [noun phrase]Vocabulary
Synonyms
Strong
Neutral
Weak
Vocabulary
Antonyms
Usage
Context Usage
Business
Critiquing market bubbles or poor strategic decisions: 'The irrationality of the recent buying frenzy was clear to analysts.'
Academic
In psychology, philosophy, economics: 'The study explores the cognitive roots of decision-making irrationality.'
Everyday
Describing frustrating behavior: 'I can't understand the irrationality of his fear of pigeons.'
Technical
Mathematics: 'Euler proved the irrationality of *e*.'
Examples
By Part of Speech
adverb
British English
- He reacted quite irrationally to the minor criticism.
- The market sometimes behaves irrationally.
American English
- He reacted irrationally to the minor criticism.
- The market sometimes behaves irrationally.
adjective
British English
- His irrational behaviour worried his colleagues.
- It seemed an irrational fear to have.
American English
- Her irrational behavior worried her coworkers.
- It seemed an irrational fear to have.
Examples
By CEFR Level
- His fear of water is a kind of irrationality.
- There is no irrationality in her plan.
- The politician's speech was full of emotion and irrationality.
- Psychologists study the causes of human irrationality.
- The sheer irrationality of the policy left experts baffled.
- His argument exposed a fundamental irrationality at the heart of their economic model.
Learning
Memory Aids
Mnemonic
Think: 'IRRATIONAL-ity' — If your RATIO (logic) is all (AL) gone, you're left with IRRATIONALITY.
Conceptual Metaphor
IRRATIONALITY IS A FORCE (e.g., 'swept away by irrationality'), IRRATIONALITY IS DARKNESS/LACK OF CLARITY (e.g., 'descended into irrationality').
Watch out
Common Pitfalls
Translation Traps (for Russian speakers)
- Avoid calquing as "иррациональность" in all contexts; for 'silly behavior' use "глупость" or "неразумность". The mathematical term is correctly "иррациональность".
Common Mistakes
- Misspelling as 'irrationaly' or 'irrationalety'. Using it as a countable noun (e.g., 'an irrationality') is rare and often awkward.
Practice
Quiz
In which context is 'irrationality' used in a purely technical, neutral sense?
FAQ
Frequently Asked Questions
When applied to human thought or behavior, yes, it is negatively charged as it implies a deficit. In mathematics, it is a neutral technical term.
It is almost exclusively uncountable. Using it in the plural ('irrationalities') is very rare and stylistically marked, typically found in philosophical prose.
'Irrationality' specifically refers to a lack of logical reasoning, which can be temporary or situational. 'Stupidity' is a broader, more offensive term implying a general lack of intelligence.
There is no direct verb. Related concepts are expressed with phrases like 'act irrationally' or 'behave without reason'. The adjective is 'irrational' and the adverb is 'irrationally'.
Collections
Part of a collection
Abstract Thinking
B2 · 49 words · Words for ideas, reasoning and intellectual concepts.
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