01
irrational
Not in accordance with reason or logic; inaccessible to, or contradicting, rational understanding.
example
Seine Angst vor Spinnen ist völlig irrational.
His fear of spiders is completely irrational.
irrational
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Meanings
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Usage tips
Word structure
The word consists of the prefix 'ir-' and the word 'rational'. The prefix 'ir-' is a variant of 'in-' and means 'not'. So 'irrational' literally means 'not rational' or 'unreasonable'.
EXAMPLE
Es ist irrational, ohne Jacke bei Kälte nach draußen zu gehen.
It is irrational to go outside in the cold without a jacket.
Context clues
You can easily recognize the meaning from the context. If people are talking about feelings, behavior, or decisions, the general meaning 'unreasonable' is meant. In the context of mathematics, numbers, or formulas, the specific mathematical meaning is meant.
EXAMPLE
Ihre plötzliche Wut war völlig irrational.
Her sudden anger was completely irrational.
Typical collocations
In the general meaning, 'irrational' is often connected with human reactions and thoughts. Common combinations are 'eine irrationale Angst' (an irrational fear), 'irrationales Verhalten' (irrational behavior), or 'eine irrationale Entscheidung' (an irrational decision).
EXAMPLE
Er hat eine irrationale Angst vor geschlossenen Räumen.
He has an irrational fear of enclosed spaces.
Mathematical use
In mathematics, this adjective is used almost exclusively in the fixed expression 'irrationale Zahl' (irrational number). It describes numbers that cannot be represented as a fraction.
EXAMPLE
Im Unterricht haben wir über rationale und irrationale Zahlen gesprochen.
In class, we talked about rational and irrational numbers.
Compare with
irrational vs vernünftig
reasonable / decent
'vernünftig' and 'irrational' are opposites when it comes to thinking and decisions. 'vernünftig' describes something that is sensible, well considered, and done for good reasons. 'irrational' describes something that does not fit with reason or logic, often because strong emotions or fears determine the decision. Learners may confuse the words because both have to do with reason. The direction is important: 'vernünftig' fits with reason, while 'irrational' contradicts it.
irrational
Nach dem Gespräch merkt er, dass seine Angst vor dem Anruf irrational ist.
After the conversation, he realizes that his fear of the phone call is irrational.
vernünftig
Der Lehrer schlägt vor, das Training morgen vernünftig zu planen.
The teacher suggests planning tomorrow's training sensibly.
In real life
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