事由|じゆうjiyuu[0]heiban (flat)

1. nounreason; cause; whys and wherefores; particulars

• Synonym理由りゆうNeutralThe everyday, most common word for a reason or cause; covers a far wider range of uses, while 「事由」 leans legal-official, denoting the concrete facts behind a result.
• Synonym訳わけNeutralColloquial word for a reason or cause; it also means 'meaning', and, unlike 「事由」, is not tied to legal or official documents.
• Synonym所以ゆえんWrittenWritten, literary word for the reason something is so; more elegant and old-fashioned than 「事由」, which leans legal-official.
• Related理屈りくつNeutralLogic or reasoning, often strained — as in 「屁理屈」 (a lame excuse); unlike 「事由」, it concerns argument rather than the facts constituting a cause.
• Related根拠こんきょNeutralBasis or grounds — the support something rests on; it stresses proof or evidence, unlike 「事由」, which names the concrete facts behind a result in legal-official use.
• Related事情じじょうNeutralCircumstances — the situation or conditions behind something; stresses where things stand, unlike 「事由」, which in legal-official use names the facts causing a result.
• Related道理どうりNeutralReason as what is logical or right; stresses whether something makes sense, unlike 「事由」, which names concrete causal facts in legal-official use.
• RelatedいわれNeutralThe origin or history behind something; it stresses where a thing comes from, unlike 「事由」, which in legal-official use names the facts causing a result.
• Related原由げんゆWrittenA written, less common word for the cause or origin of something; it lacks the legal-official flavor of 「事由」.

「事由」 is for the concrete facts that bring about a result, with a legal or official-document flavor, as in 「解雇事由」 and 「やむを得ない事由」. In everyday speech say 「理由」 or 「訳」; for grounds or evidence use 「根拠」, and 「所以」 in written prose.

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

1. 事ことの理由りゆう。
2. 直接ちょくせつの原因げんいんや理由りゆうと成なっている事実じじつ。