Meaning & use
irrational
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Meanings
adjectivecomparable
Not based on clear thinking or good reasons, often because of strong feeling.
Grammar: Used before a noun or after a linking verb: an irrational fear, he was irrational.
Patterns
- an irrational fear
- it is irrational to do something
Her fear of small dogs was irrational, but it felt real.
It is irrational to panic over one bad grade.
He made an irrational decision when he was angry.
adjectivenot comparablemathematics
Describing a number that cannot be written as a fraction of two whole numbers.
Grammar: Used in mathematics: pi is an irrational number.
Patterns
- an irrational number
The square root of two is an irrational number.
Pi is irrational, so its decimals never repeat.
Students learn that irrational numbers cannot be written as simple fractions.
Word forms
| comparative | more irrational |
|---|---|
| superlative | most irrational |
Common combinations
- irrational fear
- He has an irrational fear of elevators.
- irrational behavior
- Stress can lead to irrational behavior.
- completely irrational
- Her anger was completely irrational.
- irrational number
- An irrational number has a never-ending decimal.
- irrational decision
- Buying that old car was an irrational decision.
Synonyms and how they differ
- illogical
- Illogical points to a flaw in the reasoning itself, while irrational suggests that feeling is behind the thinking.
- unreasonable
- Unreasonable criticizes demands or behavior as unfair, whereas irrational criticizes lack of sound thought.
- absurd
- Absurd is stronger, suggesting something is ridiculous, while irrational can describe an understandable emotion.
- groundless
- Groundless applies only to claims or fears without basis, a narrower use than irrational.
Opposites
Word family
- irrationality noun
- the quality of being illogical
- irrationally adverb
- in a way not based on reason
- rational adjective
- based on reason and clear thinking
- rationality noun
- the quality of being reasonable
- rationalize verb
- to explain behavior with reasonable-sounding excuses
Commonly confused: irrational or irrelevant?
irrational vs irrelevant
Irrelevant means not connected to the topic, whereas irrational means not based on reason.
Practice
Which describes an irrational fear?
Choose one answer.
An irrational fear has no sound basis, as with a harmless spider. The other fears have clear, reasonable causes.
Make it your own
Write a sentence using “irrational”, then check it and compare it with the examples above.