What does irrationalise mean?
Irrationalise means to make something irrational: to deprive it of sound reasoning, logical consistency, or balanced judgement. The verb can also describe a person behaving irrationally, although this use is less common. A speaker might accuse a campaign of irrationalising public opinion by presenting an issue in inflammatory terms, while a board might reject a proposal that would irrationalise the allocation of resources. The word is more precise than simply saying “to make worse”, because it specifically identifies the abandonment or distortion of reason. British English generally uses the -ise spelling, whereas American English uses irrationalize. In both varieties, the term carries a strongly critical connotation and implies that rational thought has been undermined rather than merely complicated. Its relatively formal register makes it suitable for analytical or critical writing, though it is more commonly encountered in journalism, academic discussion, and political debate than in everyday conversation.
verbTo make something irrational or contrary to reason. It can also mean to behave irrationally.
- To make irrational, unreasonable, or contrary to logic.
- To act in an irrational way.
"Fear of the unfamiliar can irrationalise even the most sensible decision."
"The committee refused to let one vocal member irrationalise the entire discussion."
"As the deadline approached, he began to irrationalise his plans and abandon them one by one."
Irrationalise means pushing logic off the rails—though British spelling keeps the emphasis rather literally on the rails.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does irrationalise come from?
The word combines the Latin prefix in- meaning “not” with rational, from Latin rationalis, meaning “of or according to reason.” The verb was formed in the 19th century on the model of rationalize and its opposite, irrationalize. Its cognates include rational, ration, and ratio, all of which ultimately derive from the Latin ratio, meaning “reason” or “proportion.”
Related word forms
How irrationalise is actually used
The -ise spelling is standard in British English, while -ize is used in American English. The word is relatively formal and often describes a process by which logic, judgement, or public discourse is made less reasonable.
Easily confused with irrationalise
To rationalize is to make something appear reasonable or logically defensible, whereas to irrationalize is to make it less reasonable.