Translation guide
The English word 'reason' can be expressed in Japanese through several words and patterns, depending on whether you mean a cause, a motive, a logical basis, or an excuse. The most common and versatile word is 理由 (riyuu), but other options like 原因 (gen'in) for cause, わけ (wake) for natural conclusion, and せい (sei) for blame are also important. This guide helps learners choose the right expression for each situation.
Expressing a reason, basis, or grounds for something in a neutral or formal context.
The most common and versatile word for 'reason'. It can be used in both formal and informal settings, and covers a wide range of meanings from cause to excuse.
遅刻の理由を説明してください。
Please explain the reason for your lateness.
彼が辞めた理由は何ですか？
What is the reason he quit?
Often used to express a reason that is a natural conclusion or logical outcome. It can also be used to deny a reason or to ask for an explanation. More conversational than 理由.
そういうわけで、私は行けません。
For that reason, I can't go.
Refers to circumstances or reasons behind a situation, often implying some complexity or personal circumstances. Used in formal contexts.
Expressing the cause of an event, especially an accident, problem, or natural phenomenon.
Expressing a personal motive, intention, or the reason behind one's actions.
Specifically means 'motive', often used in contexts like crime, decisions, or actions. More formal than 理由 when talking about personal drives.
Expressing a reason that is an excuse or a pretext, often not the real reason.
Expressing a logical basis, rationale, or grounds for a conclusion.
Means 'basis' or 'grounds', often used in arguments, claims, or legal contexts. It refers to the evidence or logical foundation for something.
Expressing 'reason' in the sense of connecting clauses with 'because' or 'since'.
The most common way to say 'because'. It attaches to the plain form of verbs, adjectives, and nouns (with だ/です). It can be used in both casual and polite speech.
雨が降っているから、傘を持って行きます。
Because it's raining, I'll take an umbrella.
理由 (riyuu) is the general word for 'reason' and can be used for both causes and motives. 原因 (gen'in) specifically means 'cause' and is used for events, accidents, or problems. わけ (wake) often implies a logical conclusion or natural reason, and is common in conversational Japanese. Use 理由 when in doubt.
理由：遅刻の理由は寝坊です。
Reason: The reason for being late is oversleeping.
原因：事故の原因はスピード違反です。
Cause: The cause of the accident is speeding.
What's the reason you were late? (casual)
I quit the company due to family reasons.
Specifically means 'cause' as opposed to 'reason'. Used for the direct cause of an event, often negative or neutral. Not used for personal motives.
事故の原因を調査しています。
We are investigating the cause of the accident.
火事の原因はタバコの不始末だった。
The cause of the fire was careless handling of a cigarette.
Used to assign blame or indicate a negative cause. Often translated as 'fault' or 'because of (negative thing)'. It attaches to nouns or plain form verbs/adjectives.
雨のせいで試合が中止になった。
The game was canceled because of the rain. (implying it's the rain's fault)
あなたのせいで遅刻した。
I was late because of you. (blaming)
犯行の動機は何ですか？
What was the motive for the crime?
彼が立候補した動機は純粋なものだった。
His motive for running for office was pure.
Also commonly used for personal reasons, though less specific than 動機.
彼女と別れた理由は何？
What's the reason you broke up with her?
Means 'excuse' or 'justification'. It often implies that the reason given is not entirely true or is an attempt to avoid blame.
言い訳は聞きたくない。
I don't want to hear your excuses.
彼はいつも言い訳ばかりしている。
He's always making excuses.
Means 'pretext' or 'excuse', often used when someone uses a false reason to hide their true intentions. More formal than 言い訳.
彼は病気を口実に会議を欠席した。
He used illness as a pretext to skip the meeting.
その主張には根拠がない。
There is no basis for that claim.
科学的な根拠を示してください。
Please show the scientific basis.
Means 'reasoning' or 'justification', the act of giving reasons. Often used in academic or analytical contexts.
彼の理由付けは説得力がある。
His reasoning is persuasive.
Since I'm tired, I'll go to bed early.
A slightly more formal or polite way to say 'because'. It is often used to give a reason in a softer, more objective manner. Attaches to plain forms, but な-adjectives and nouns use な before ので.
電車が遅れたので、遅刻しました。
I was late because the train was delayed.
静かなので、ここが好きです。
I like it here because it's quiet.
A formal pattern meaning 'because of' or 'due to'. It can be used with nouns (のため) or verbs/adjectives in plain form. Often used in written or official contexts.
台風のため、飛行機が欠航になった。
Due to the typhoon, the flight was canceled.
事故があったために、道が渋滞している。
Because there was an accident, the road is congested.
No wonder he's angry. (lit. It's a reason he gets angry.)
English often uses 'the reason why... is because...', but in Japanese, this structure is redundant. Simply use 理由は〜からです or 理由は〜ことです. Avoid directly translating 'why' as なぜ in this pattern.
遅刻した理由は、電車が遅れたからです。
The reason I was late is that the train was delayed.
わけ：彼が怒るわけだ。
No wonder he's angry. (lit. It's a reason he gets angry.)
English often uses 'the reason why... is because...', but in Japanese, this structure is redundant. Simply use 理由は〜からです or 理由は〜ことです. Avoid directly translating 'why' as なぜ in this pattern.
遅刻した理由は、電車が遅れたからです。
The reason I was late is that the train was delayed.