のだ（んだ） (noda) Meaning Japanese Grammar - Explanations

のだ (noda), or its contracted form んだ (nda), is an auxiliary verb that is used for:

• Expressing a reason or an explanation
• For emphasis

のだ to express a reason or explanation

Let's see a simple example to understand the use of のだ.

A friend of yours asks you if you can would like to come for a drink, but you explain that you have an exam and you can't:

As you can see, in answering the question んだ is used at the end of the sentence.

んだ usually cannot be translated with any words, it mainly changes the nuance in meaning of the sentence (explanation)

んだ expresses the fact that the answer implies an explanation. In fact, the phrase I have an exam Monday. is used to explain the reason why you can't come.

だ / です and のだ

This use of のだ expresses a similar meaning to だ (da) or です (desu) when taken individually (express a reason, to be).

The addition of の serves to accentuate the fact that what we say is a reason or explanation, giving more emphasis to this meaning.

Use of んです: audio and explanation

のだ to express emphasis

のだ is also used to express emphasis. It can be interpreted as an exclamation (adding the exclamation point !).