I'm having trouble understanding the best way to respond to someone asking "why".

My study guide advised,

To answer the question with "why", make a statement sentence that indicates the reason and add からです at the end,
A: どうして昼ご飯を食べなかったんですか   B: ダイエットをしているからです

Feeling like it couldn't possibly be that simple, I went looking to see if anyone had explained things in more detail.

However, nearly every sentence with から I found are sentences that describe both the cause and response, seemingly not as a response to a "why" question, such as this sentence taken from another post


I haven't been able to find much at all on からです in direct response to a question, as it was in my book's example.

I figured the most likely reason for this was either
A. からです is a nonstandard approach and my book is weird, or
B. I've missed something.

Unfortunately, B prompted me to wonder if some of these descriptions actually were a direct response that I was misunderstanding.

So, while I was searching for something like

A: どうして外に行かなかったんですか
B: 雨が降っていたからです

People were actually saying

A: どうして外に行かなかったんですか
B: 雨が降っていたから、外に行きませんでした

In short, is something like "ダイエットをしているからです" actually a standard way to give a reason in response to a question? If not, what would be more appropriate?

Any other ways to give a reason are welcome, because nuance is neat.

  • 1
    It seems there are a lot of questions here but i don't really know what you are asking. this might help if you are looking for references to the pattern: ( eow.alc.co.jp/search?q=るからです&ref=sa )
    – yadokari
    Aug 17, 2012 at 1:22
  • 1
    @Kathryn Welcome to JLU! It seems what your asking could be clarified much more by simplifying your post. From what I understand so far, you want to know the various ways you can explain a "reason" when being presented with a question. Is that correct?
    – Chris
    Aug 17, 2012 at 1:29
  • @Chris Yes, that was what I was trying to ask. Thank you both so much for your kindness in the face of that eldritch horror. I've done some editing, hopefully now it at least resembles sense. If not, please let me know.
    – Kathryn
    Aug 17, 2012 at 12:10
  • Welcome! I've had the same question too. I've never actually heard -からです in conversation, but my book says that that's how you respond to a question. Normally I respond with ですから, んです, or のです I'm not sure the difference between ですから and からです but the former is the one I've heard the most often. Aug 17, 2012 at 13:38

2 Answers 2


I think we'd say/write like this when we need to sound formal/polite:

  • ダイエット(を)して(い)るからです/雨が降って(い)たからです

We normally say 「ダイエットしてるんです。」「雨が降ってたんです。」etc. in polite speech

And in casual speech:

  • 「ダイエットしてるの。」(feminine)
  • 「ダイエットしてるんだ。」(masculine)
  • 「ダイエットしてるんだもん。」(feminine, cute)
  • 「ダイエットしてるから。」
  • 「ダイエットしてるもんで。」
  • 「雨が降ってたの。」(feminine)
  • 「雨が降ってたんだ。」(masculine)
  • 「雨が降ってたんだもん。」(feminine, cute)
  • 「雨が降ってたから。」
  • 「雨が降ってたもんで。」et cetera

The が after 雨 can often be left out when we talk casually.

~~てるんだ/です in ダイエットしてるんだ/です and ~~てたんだ/です in 降ってたんだ/です are shortened (contracted?) forms for ~~ているのだ/です and ~~ていたのだ/です, respectively. (The "い" and the "o" in "の" are dropped.) 

  • Just a note: the んだ forms are no longer that masculine. The の forms are almost old-fashioned now.
    – Angelos
    May 16, 2015 at 18:34

Look up these expression: ~ものですから (formal) ~もんだ (casual)

http://www.guidetojapanese.org/learn/grammar/genericnouns (i.e. もの)

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