だ vs のだ – What’s the Difference between da and noda in Japanese?
INDEX
Explaining a Situation
When you are explaining something to someone who has no background knowledge you would not use のだ.
太郎は学生だ
Taro is a student
However, you can use のだ if you are adding more information or an explanation like below:
太郎は大学にいる。彼は学生なのだ
Taro is at the university. He is a student
Here, the first sentence lets us know that Taro is at school. Then the next sentence adds an explanation of why he is there.
Asking for an Explanation
When someone is simply asking a question they may ask:
買い物に行きませんか？
Would you like to go shopping? (Are you not going shopping?)
But, assume that the speaker knows that the person they were asking is planning on shopping:
買い物に行かないのですか？
Are you going shopping (or not)?
Weren’t you planning on going shopping?
In the above situation since the speaker thought the listener was going to go shopping, you can use のだ. Or, since it is a question, のですか. Now, this no longer a simple question but instead the speaker wants an explanation on why they changed their mind, or why they still have not left yet.
Providing a Reason
Continuing with the example above, imagine that the person being asking about shopping is sick in bed. They could respond in two ways:
私は病気です
I am sick
私は病気なんです
I am sick (as you can see / as you know)
The difference here would be that in the first example it was not obvious that the person was sick. The second example would be used when the person that was asking about shopping knew that the person was sick.
Making a Request or Proposal
In certain situations when someone is making a request or proposal, they make use のだ or のです.
明日休みなんですが、一緒に映画でも見に行きませんか
I am off (of work etc.) tomorrow. Would you like to see a movie with me or something?
In these situations, the person making the proposal will explain a situation with のだが or のですが and then follow it up with there proposal.
Expressing Thoughts or Opinions
Finally, when someone wants to share there thoughts or opinions about something they may use のだ.
この近所はちょっと不便なところがありますが、住みやすいんですよ
There are some inconveniences about this neighborhood but it is a nice place to live
Here, the speaker is trying to appeal to the listener that this is a nice place to live regardless of some inconveniences. If the speaker were to leave out the んです then it would just sound like they were providing information.
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