Translation guide
The English word 'why' is used to ask for a reason or cause, to express surprise or objection, or to suggest something. In Japanese, the most common equivalent is なぜ (naze) or どうして (doushite), but the choice depends on formality, politeness, and context. Direct translations like なぜ are often used in formal or written contexts, while どうして is more common in casual speech. In many situations, especially when making suggestions or expressing surprise, Japanese uses different structures rather than a direct 'why' question.
Why? (formal/written)
Polite and suitable for formal situations.
The speaker wants to know the reason or cause behind an action, event, or state.
The standard word for 'why' in formal and written Japanese. Can be used in both questions and embedded clauses. In polite speech, add ですか.
Why were you late?
I don't know why he was chosen.
Common in spoken Japanese, slightly more emotional or emphatic than なぜ. Can sound casual or childlike in formal settings. Often used to express surprise or disbelief.
Very casual and common in everyday speech. Often used among friends or in informal situations. Can be considered rude in formal contexts.
A polite pattern to ask 'why is it that...?' by nominalizing the preceding clause with の. Common in formal speech and writing.
Why did he quit? (lit. Why is it that he quit?)
Literally 'what is the reason for...?' More formal and explicit. Used in official inquiries or written reports.
The speaker is not necessarily asking for a reason, but expressing shock, disbelief, or objection to something.
The speaker is suggesting an action or offering an alternative, not asking for a reason.
Standard polite suggestion meaning 'Why don't you...?' or 'How about...?'. Literally 'How would it be if you...?'
The speaker is not directly asking 'why', but using it within a larger sentence (e.g., 'I wonder why...', 'Do you know why...?').
Standard way to embed a 'why' question. The か marks the embedded question. In polite speech, use なぜ～か as is, or なぜ～のか for emphasis.
When making suggestions, English often uses 'Why don't you...?' or 'Why not...?'. Directly translating these as なぜ～しないの？ sounds like you are asking for a reason, not making a suggestion. Use patterns like ～たらどうですか or ～てみませんか instead.
Why don't you go to a movie?
Why did you do that?
Polite but with explanatory ん.
どうして来なかったの？
Why didn't you come?
Why did you do such a thing?
Why do you say that?
Why are you here?
What is the reason for your lateness?
Often used rhetorically to express surprise or objection, similar to 'How could you?' or 'Why would you...?'
How could you do such a thing?
Why didn't you tell me?
Casual and emphatic, often used to express strong surprise or objection.
Why the hell would you do that!
Literally 'why again', used to express surprise or exasperation at something unexpected or repeated.
Why on earth would you do that?
Why don't you take a break?
Why don't you ask him?
Casual version of ～たらどうですか, used among friends or in informal situations.
Why don't you go home already?
Casual suggestion meaning 'Why not try...?' or 'Why don't you try...?'
Why don't we try this restaurant?
Polite version of ～てみない, suitable for invitations or formal suggestions.
Why don't we start a new project?
A slightly more formal alternative to ～たらどうですか, meaning 'How about doing...?'
Why don't you make a reservation early?
Do you know why he didn't come?
I wonder why such a thing happened.
Casual embedded question, common in spoken Japanese.
I don't know why she is angry.
Very casual embedded question, used among close friends.
I can't understand why that guy was chosen.
These three words all mean 'why', but differ in formality and nuance. なぜ is formal and neutral, suitable for writing and polite speech. どうして is more emotional and common in spoken Japanese; it can express surprise or accusation. なんで is very casual and should be avoided in formal situations. In polite conversation, どうしてですか is acceptable, but なぜですか is safer.
Adding の (or ん in casual speech) before ですか or だ makes the question sound more explanatory or seeking an explanation. For example, なぜ来なかったのですか？ (Why is it that you didn't come?) sounds more natural than なぜ来ませんでしたか？ in many contexts.
I don't know why.
Formal.
Why not?
When agreeing or suggesting, not asking for a reason.