訳|わけwake[1]atamadaka (head-high)

1. nounreason; cause; grounds
   そういうわけで私はこんなに早はやく帰かえって来きたのです。↗

   That's why I came back so soon.
2. nounmeaning; sense
3. noun(good) sense; reason
4. nouncircumstances; case
5. noun(romantic) relationship; love affair

• Synonym理由りゆうNeutralThe neutral word for the reason behind something, leaning formal and objective, as in 「理由を説明する」; 「訳」 is more colloquial and also covers sense and meaning.
• Synonym根拠こんきょWrittenThe written-style word for the basis or evidence supporting a claim, as in 「根「根拠のない噂」; it stresses proof rather than the reason itself.
• Synonym事由じゆうWrittenA written term of legal and official documents for the particulars of a matter, as in 「退職事由」; not used in everyday speech.
• Synonym事情じじょうNeutralA neutral word for the whole story and situation around a matter, as in 「家庭の事情」; the emphasis is on circumstances rather than the reason itself.
• Synonym道理どうりNeutralThe neutral word for a reason that squares with fairness and common sense, as in 「道理で〜わけだ」, meaning no wonder.
• Synonym一理いちりWrittenA written word for a measure of truth, a point that holds to some extent, as in 「一理ある」; used when you partly agree.
• Synonym筋合すじあいWrittenA written word for the grounds that make something only right or due; often in the negative, as in 「言われる筋合いはない」.
• Synonym所為しょいWrittenAs 「しょい」, a written and rare word for one's deeds; in colloquial blame the reading is 「せい」, as in 「君のせいだ」.
• SynonymいわれWrittenA written word for the origin or story behind a thing, as in 「地名の謂れ」; also in 「謂れのない非難」 for groundless criticism.
• Synonym所以ゆえんWrittenWritten language for why something is as it is, as in 「人の人たる所以」; literary, not for conversation.
• Synonym訳柄わけがらWrittenA written word for the reason and circumstances of a matter; very rare — say 「訳」 or 「事情」 in daily speech.
• Synonym原由げんゆWrittenA written word for the cause or origin of a matter; very rare — say 「原因」 in daily speech.
• Synonym成因せいいんWrittenA written word for the cause behind how something forms; mostly in scientific contexts, as in 「地形の成因」.
• SynonymかどWrittenA formal noun for the matter that serves as grounds, mostly in suspicion or charges, as in 「窃盗の廉で」.
• Related由来ゆらいWrittenA written word for where a thing comes from — its origin, as in 「名前の由来」; the focus is on source, not on why something happened.
• Related理屈りくつNeutralA neutral word for reasoning or logic, often with a nuance of strained logic or excuse, as in 「理屈をこねる」.
• RelatedわけあいCasualA colloquial word for the reason and circumstances, but with an old-fashioned ring; little used today.

For a reason or cause in everyday speech, 「訳」 is the default. Use 「理由」 when stating a reason formally, 「根拠」 for the evidence behind a claim, 「由来」 or 「謂れ」 for origins, 「事情」 for circumstances, and 「道理」 or 「理屈」 for logic and sense. 「事由」 belongs to legal and official writing. The rest are rare or specialized: 「訳柄」 and 「原由」 are written and uncommon, 「訳合」 is old-fashioned, 「成因」 is scientific, 「廉」 appears in charges, 「所以」 is literary, 「一理」 grants partial truth, and 「筋合」 usually appears in negatives.

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

1. （わけ、訣わけの代用だいよう）理由りゆう。