What's the difference between なぜ、どうして and なんで when meaning 'why'?

Question

I've been meaning to ask this for a while. What is the difference between these 3 words. I was taught they all mean "why", but obviously, being different words they convey different nuance and would be used in different situations. What would be the difference between these 3 sentences and in what situations would they be used? なぜここにいるのですか？ どうしてここにいるのですか？ なんでここにいるのですか？

Answer 1

They differ in levels of formality, with なぜ being the most formal and なんで being the least. Generally speaking, this means you could use なんで among friends or close family, but certainly not teachers or your boss. どうして is somewhat middle ground and could more or less be used among equals, while なぜ is formal. These should match the level of formality of your sentence structure too (ex: If you're using keigo, don't used なんで or どうして).

If we're talking about formal writing, like a paper for a class or a work document, なぜ is a standard choice unless you have good reasons for another.