At a certain point in learning Japanese, you will have come across the words なぜ (naze), どうして (doushite) and なんで (nande), which are all interrogative adjectives that mean why. Perhaps you learned どうして first, but now with three options to choose from the challenge is choosing the most appropriate one to use in a given situation. Knowing the subtle difference between them will help you choose correctly.
The difference between なぜ (naze), どうして (doushite) and なんで (nande) is that なぜ is a more formal term for asking why and is purely an inquiry about the reason or cause of something, whereas どうして and なんで are casual terms which can be used to convey a speaker’s emotion when asking why.
Below we will look at なぜ, どうして and なんで in turn. Detailed definitions and example sentences for each should give you a good feel for each of them.
なぜ (naze)
Meaning: (Interrogative adverb). Why? Used in the purest sense of asking for the reason or cause of something. There is no emotion from the speaker, just intellectual curiosity. なぜ is the most formal way to ask why in Japanese and is often used in business and other formal situations. Kanji form: 何故. Kanji Breakdown: 何 – what 故 – reason, cause, circumstances Example Sentences: なぜ、この橋は自転車が渡れないのですか？ Why can't bicycles cross this bridge? この製品の納期がそこまで長いのはなぜでしょうか？ Why is the lead time for this product so long? なぜ電子機器の製造に銅が必要なのか？ Why is copper needed for making electronic devices?
どうして (doushite)
Meaning: (Interrogative adverb). Why? Used when asking the reason or cause of something. Often charged with the speaker’s emotions about a particular situation. It is more casual than なぜ. In some cases, どうして is used rhetorically in which the speaker is not really seeking a reason, but rather expressing their emotion, such as vexation, regret, surprise, pleasure… Kanji form: 如何して. Kanji Breakdown: 如 – like, such as, as if 何 – what Example Sentences: どうしていつもバスが遅れるの？ Why is the bus always late? コーヒーにシナモンをかけると、どうしていつもこんなにおいしいんだろう？ Why does coffee always taste so much better with cinnamon? よりによって、どうして今日に限って声が出なくなったのか？ Of all days to lose my voice, why did it have to be today?
なんで (nande)
Meaning: (Interrogative adverb). Why? Used when asking the reason or cause of something. Very similar to どうして, but even more casual. なんで is probably the most common way to ask why in casual spoken Japanese, especially by younger people and children. Kanji form: 何で. Kanji Breakdown: 何 – what Example Sentences: 何でアイツはあんなにケチなの？ Why is he so stingy? なんでコンサートに行かせてくれないの？ Why won't you let me go to the concert? なんでうちの上司はいつも土壇場で気が変わるんだ？ Why does our boss always change her mind at the last minute?
Overlap Between Why and How in Japanese
Coming back to どうして, it is worth mentioning that it has some overlap with “how”, as in, how did something happen, what was the manner in which something happened? In some Japanese-Japanese dictionaries you will probably find that definitions of どうして include the words どのようにして (donoyounishite), in which どのように means “how” or “in what way”, and どうやって (douyatte) which means “how”.
Even in English, there is a subtle difference when someone asks, why did that happen and how did that happen? In Japanese both questions could be asked by using どうして. Whether どうして means how or why will depend on the context and the tone of the speaker. Let’s look at the sentence below.
どうしてそうなった？ How did that happen? / Why did that happen?
If the speaker was purely asking for the manner in which it happened, then どうして could be interpreted as how. But if the question was charged with the speaker’s emotion, for example, frustration or regret, どうして could be interpreted as why, as in “why, oh why!”. Below is a more concrete example which contrasts どうして and なぜ.
なぜ電車は脱線したのか？ Why did the train derail? どうして電車は脱線したのか？ How did the train derail? / Why did the train derail? 何が原因で電車は脱線したのですか？ What caused the train to derail?
In the first sentence, using なぜ makes it why. If asked this way, either in Japanese or English, one interpretation is that the speaker is seeking an underlying cause. Trains should not normally derail, so perhaps the speaker is asking an expert in train and train track maintenance for the reason. Were proper maintenance procedures being followed? Were there any unusual circumstances?
In the second sentence, the use of どうして probably means how, unless the speaker was making a rhetorical emotional utterance, in which case it would be why. In the last sentence the use of 何が原因で (nani ga genin de) “what caused” makes it clear that the speaker is looking for a reason. A large tree branch may have fallen on the track, for example.
Although there is no word with the dual why/how meaning like どうして in English, a somewhat similar term exists which is the colloquial term, “how come?”, which apparently originates from the longer expression “how did it come about that” [1]. In fact, なんで is quite similar to how come. And it is also worth noting that this discussion on どうして also applies to なんで.
References:
[1] Jill Robbins. (2021). Why Do We Say, ‘How Come?’. Learning English. Voice of America.