理屈・理窟|りくつrikutsu[0]heiban (flat)

1. nountheory; reason; logic
   彼かれはその理屈りくつがわからないほどばかではない。↗

   He is too wise not to see the reason.
2. noun(unreasonable) argument; strained logic; excuse; pretext

• SynonymセオリーNeutralLoanword for theory or an established way of doing things, as in 「セオリー通り」; leans toward standard practice and carries no nuance of strained logic.
• Synonym理論りろんWrittenWritten word for a systematic, organized theory. 「理屈」 is spoken, everyday reasoning and often carries a quibbling, argumentative shade.
• Synonym道理どうりNeutralSound, legitimate reason, as in 「道理に合わない」; points to correct principles and has no negative shade, unlike the strained-logic side of 「理屈」.
• Synonym一理いちりWrittenWritten word for a measure of reason or some truth, as in 「一理ある」; used when you grant that a claim is partly right.
• Synonym論理ろんりWrittenWritten word for logic; neutral and objective, while 「理屈」 often colors an argument as self-serving justification.
• SynonymロジックNeutralLoanword for logic; at home in business and IT settings.
• Synonym筋合すじあいWrittenWritten word for one's grounds or standing, as in 「文句を言われる筋合いはない」; mostly in negative sentences.
• Related理由りゆうNeutralA reason or cause, as in 「遅刻の理由」; centers on why something happened, not on reasoning or argument.
• Related訳わけCasualColloquial word for cause or sense, as in 「訳が分からない」; covers many senses beyond reason.
• Related根拠こんきょNeutralBasis or grounds, as in 「根拠がない」; stresses evidential support rather than the argument itself.
• Related事由じゆうFormalFormal word for the cause or particulars of a matter, as in 「離婚事由」; typical of legal documents.
• Related説せつNeutralA theory, doctrine or account; stresses a viewpoint or claim rather than reasoning itself.
• Related由よしWrittenWritten, archaic word for reason, or for 'I hear that…', as in 「〜の由」; mainly epistolary.
• RelatedいわれWrittenWritten word for origin, history or grounds, as in 「謂れのない非難」「地名の謂れ」.
• Related所以ゆえんWrittenWritten word for the reason why something is so, as in 「人の人たる所以」.
• Related原由げんゆWrittenWritten word for cause or origin; rare in modern usage.
• Antonym無理むりNeutralAntonym of the sound-reasoning sense of 「理屈」: unreasonableness or forcing something; it does not contrast with the strained-logic sense.
• Antonym非論理WrittenWritten antonym: illogicality, opposed to 「理屈」 as reasoned argument.

Use 「理屈」 for reasoning that holds up — or for quibbling, strained arguments, as in 「理屈を言う」「屁理屈」. For sound principles say 「道理」, for systematic theory 「理論」, for a plain reason 「理由」. 「論理」 and 「ロジック」 cover logic, 「根拠」 grounds, 「事由」 formal causes, 「訳」 casual talk. 「無理」 is the opposite of the sound-reasoning sense; 「非論理」 opposes reasoned argument.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

1. 筋すじの通かよった論理ろんり。道理どうり。
2. 無理むりにこじつけた論理ろんり。論理ろんりだけに偏かたより、現実げんじつに合あわない口実こうじつ・説明せつめい。屁理屈へりくつ。