Explanatory んだ / のです

The colloquial forms of んだ and のだ are contractions of the の particle, commonly known as the explanatory particle and です in it's informal form, the だ copula, for declaring a statement similar to "it is". You may also use んです or のです, if you wish to be more formal.

Regardless of whether you use んだ, のだ, んです or のです, they all convey the exact same meaning except for the change in formality.

Just like with です, there is no English translation or equivalent. It is a matter of understanding how it is used in Japanese and avoid trying to convert it back into English or associating it with alternative words or phrases based on Western or Americanised rules.

The main feature of んだ and it's other forms is to add an explanatory tone to a sentence. It is used to emphasise, provide explanations or give reasons to something and may add a sense of certainty to a statement. It is often used to respond to a question or to explain something that the speaker assumes the listener does not know.

Before explaining more about the uses of んだ, let's first take a look at how to use it in a sentence.

How to use んだ

Here are the four types of predicates in Japanese and how to use them with んだ, のだ, んです and のです. This also applies to the explanatory の particle as well. Also, notice that な is needed when used with nouns and na-adjectives.

1. Verb (informal) + んだ
2. i-adjective + んだ
3. Noun + な + んだ
4. na-adjective + な + んだ

Nouns and na-adjectives in past tense form using だった don't need the added な. The reason for this is that な is being used as coupla and therefor isn't required with the informal past tense coupla だった.

• Noun (past) + だった + んだ
• na-adjective (past) + だった + んだ

While you may use past and non-past tenses, you must only use the informal forms of these words. For example, using either 暑いですんだ (atsui desu nda) or ありますんだ (arimasu nda) would be incorrect. Instead, we would use 暑いんだ (atsui nda) or あるんだ (aru nda).

If you wish to be more formal, you may use んです or even more formal by using のです. The use of んだ is the most casual when explaining or giving reason to something. You may also use の by itself to be very casual, though this is often perceived as overly Westernised and stereotypically feminine due to its softer tone in casual speech.

Remember that you can only use んだ and its other forms when providing explanations or giving reasons to something. Not only are you not able to use it with the です and ます forms, you also cannot use it with the command forms or volitional forms either as these don't make sense when used for explaining.

Also, you may only use んです or のです when used with the か particle for asking questions. However, using the question mark (?) is fine with んだ and のだ, for example: 覚悟なんだ？ (kakugo na nda?).

です vs のです / だ vs んだ

Using です or だ by themselves asserts that something is true as a matter of fact without providing any additional explanation or justification. It presents a very straightforward statement or simple sentence. For that reason, it doesn't always sound natural and may seem like a completely random statement.

While のです and its other forms convey the same meanings as です, it provides more context, explanation or justification for the statement and is often used when providing additional information or giving reasons. Because of this, のです sounds more natural.

There is no exact translation in English for the forms of です and のです so it's rather a matter of understanding how these are used in Japanese without westernised rules or equivalences. The following sections will hopefully make the differences a little more clearer but it's recommended that you get use to them being used in real Japanese sentences to fully understand the nuances.

Emphasising statements with んだ

Presenting a statement with just です or だ by themselves simply states a fact as being true but the addition of の strengthens or emphasises what is being said. It may seem similar to saying something like "it is a fact that...", in English. Let's take a look at a few similar sentences:

1. このゲームが安かった

   kono ge-mu ga yasukatta

   This game was cheap

2. このゲームが安かったんです

   kono ge-mu ga yasukatta ndesu

   (explanation/reason) this game was cheap

Sentence (1) states a simple fact that "this game was cheap" and comes across as rather bland. It is a straightforward statement without any particular emphasis or additional explanation. The speaker is simply expressing their personal observation or opinion.

Sentence (2) uses んです to add emphasis on the fact that "this game was cheap". It is either explaining the game was probably quite expensive but is now a cheaper price; or provides a reason, for example, they bought it because it was cheap.

Now Let's think about how the following statement may come across when んだ (のです) is used:

3. 私が悪いのです

   watashi ga warui nodesu

   I am the one to blame

のです being used here indicates that the speaker is providing a reason or explanation for their admission of fault, possibly also seeking understanding or showing sincerity and may be interpreted in English as: "You see, it's my fault, because..." or "The reason it happen is because it's my fault.".

Using only です alone without の would only present a simple fact of taking responsibility or admitting fault. It comes across as a straightforward admission of fault without the emphasis of explaining or giving reason to what happened, for example: "It's my fault".

Seeking an Explanation or Reason

Asking a question may be as simple as adding か, the marker of the unknown, to ask a question but that alone only asks a question without indicating that the speaker is seeking an explanation or reason for what is being asked. This is where んだ comes in, for example:.

1. この森にフシギダネって出ますか

   kono mori ni fushigidane tte demasu ka

   Do "Bulbasaur" appear in this forest?

Here, in sentence (1), the speaker asks a straightforward question asking "Do Bulbasaur appear in this forest?" which is a neutral question about the presence of Bulbasaur in the forest without seeking any additional information. It could simply be answered with either a Yes or No response.

2. この森にフシギダネって出るんですか

   kono mori ni fushigidane tte deru ndesu ka

   Do "Bulbasaur" appear in this forest? (seeking an explanation)

With the use of んですか in sentence (2), the speaker adds an explanatory-seeking tone to the question which implies that they are seeking more detailed information. They are likely wanting more than just a simple yes/no answer.

This emphasises that the speaker is lacking understanding or knowledge and they wish to fill in that gap of information they are unaware of. In other words, the speaker does not know if Bulbasaur appears in this forest so they are asking to find out if it is true and if there's any more details.

The listener may even respond to the question with んです in return to provide an explanation.

※ Example sentences (2) was taken from ポケットモンスター Let's Go! (Pokemon Let's Go!).

Realisation with んだ

Let's take a look at another sentence but this time notice the difference in emphasis:

1. そんなことが起きてた

   sonna koto ga okiteta

   That kind of thing was happening

2. そんなことが起きてたんだ

   sonna koto ga okiteta nda

   That kind of thing was happening (Realisation)

In sentence (1), we end with the verb 起きてた meaning "was happening" or "had happened" in the past continuous tense and states this as a plain fact without any additional emphasis.

Sentence (2) on the other hand uses んだ which provides a stronger emphasis on the significance of the statement; this expresses the speaker's realization or discovery of something that had been happening or had happened.

For that reason, sentence (2) sounds more natural as it's also emphasising the feelings of the speaker. It may also be used if you’re explaining something to yourself. In this case, んだ indicates that the speaker was not previously aware of the information. It may even be expressed as the speakers surprise at the realisation: "Ah, so that's what was happening".

※ Example sentences (2) was taken from the game 妖怪ウォッチ (Youkai Watch).

Related Lessons and References

Here is a list of other pages as a reference of what else you may be interested in reading: