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When I learnt this grammar point a while ago, my teachers told me not to use
it with "から". There reasoning for this was that のだ already implies a reason or
supporting information for a conclusion.

Even reading through the answers for "[What connotation does なんだ
add?](https://japanese.stackexchange.com/questions/1859/what-connotation-does-
add)", it appears のだ is contrasted with から.

However, I see and hear this construction (んだから）all the time. It doesn't seem
very rare at all, which leaves me confused as to why my native Japanese
teachers told me that it was incorrect in the first place.

I'll use the first result from Google as the example.

> お兄ちゃんのことがぜんぜんすきじゃないんだからねっ！！

This is a title for a movie. However, how would this be different if the title
had have been:

> お兄ちゃんのことがぜんぜんすきじゃないんだっ！！

If のだ is used as a way to indicate reason, then why is から also included? When
would it be correct to use のだから instead of のだ?
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question
grammar formal-nouns contractions copula
のだから vs のだ (んだから vs んだ）
> お兄ちゃんのことがぜんぜんすきじゃないんだからねっ！！  
>  This is a title for a movie. However, how would this be different if the
> title had have been:  
>  お兄ちゃんのことがぜんぜんすきじゃないんだっ！！

1) That's because I really don't like him!  
2) I really don't like him!

> If のだ is used as a way to indicate reason, then why is から also included?
> When would it be correct to use のだから instead of のだ?

With のだ, you _may_ say there is a reason. You may implicitly make a
cause/consequence relation or a correlation. You were maybe not directly asked
the reason to which you reply.  
A: Doesn't he sing well?  
B: I don't care, I don't like him anyway!

With のだから, you emphasise that THIS IS the reason.  
A: Why don't you marry him?  
B: Because I dislike him! Are you stupid or what?
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answer
Perhaps your teachers told you ～のだから (～んだから) is incorrect not because it is
never used (you already know it's very common) but because you can't simply
drop it into any sentence.

While digging around on Google, I came across [a very nice
PDF](https://web.archive.org/web/20130120054607/https://www.jpf.go.jp/j/japanese/survey/tsushin/grammar/pdf/grammar201009.pdf)
published by the Japan Foundation which explains the use of ～のだから. You can
read it on your own (it's even got 読み仮名!), but I'll summarize the main points
here.

### Rules for ～のだから

  1. Used when _both the speaker and listener know some fact_ , but expresses a strong feeling on the part of the speaker that the listener, although conscious of said fact, _does not fully appreciate its implications_. (I have also seen this expressed as a _mismatch between the speaker's and listener's perception of some matter_.)
  2. The clause following ～のだから often expresses the speaker's judgment, intent, wish, or request.

### Example 1

A mother tells her children, 「10時半のバスに乗る **から** 、早く支度しなさい。」 ("We're taking the
10:30 bus, so hurry up and get ready to go."). The children, however, are
occupied with other things and don't do much in the way of getting ready. So
the mother comes back and says, 「10時半のバスに乗る **んだから** 、早く支度しなさい。」 ("[Hey, I
know you know] we're taking the 10:30 bus, so hurry up and get ready to go.").
～から is used in the first sentence because it's new information and simply
provides a reason for the latter clause. But ～のだから is used in the second
because the children are aware of the fact that they're taking the 10:30 bus,
yet their failure to get ready to leave shows that they don't fully appreciate
its importance. ～のだから adds emphasis and serves to pull the listener's point of
view around to the same side as the speaker's.

### Example 2

A student comes up to a teacher and says, 「用事がある **んですから** 、早めに帰りたいんですが。」 ("I
have a prior obligation, so I'd like to leave early [if I could]…."). The
teacher feels offended by this, because the use of ～のだから implies that the
teacher should be aware of the fact that the student has something scheduled,
when in fact the teacher has no such knowledge. (A better sentence would be
「用事があります **ので** 、早めに帰りたいんですが。」 because ～ので does not presume that the listener
already knows whatever precedes ～ので.)

There's a four-problem quiz in the linked PDF which is left as an exercise to
the reader.

### お兄ちゃんのことがぜんぜんすきじゃないんだからねっ！！

Context would help a bit here, but just as a guess, this is best filed under
the "mismatch between perceptions" category of ～のだから: お兄ちゃん sees his 妹's
actions as signs that she might actually like him, but in reality that's not
the case, so 妹 decides to set the record straight and make sure she and お兄ちゃん
are on the same page with ～のだから (the implication being that お兄ちゃん should be
well aware of this fact, but from 妹's perspective, he doesn't seem to be fully
appreciative of it).
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answer
Here `だから` is more for implying that the speaker does not want the listener to
misunderstand. A full sentence could be:

> あなたのこと好きじゃないんだから、勘違いしないでね。  
>  I don't like you, so don't misunderstand it.  
>  あなたのこと好きじゃないんだから、まるで私が好きかのようにふるまわないでください。  
>  I don't like you, so don't act as if I like you.

Whether you should use `のだから` or not depends on what kind of sentence you're
building. `のだ` could be for **explanation** ,

> 妹は私のことが嫌い **なのだ** 。だって、このあいだ「お兄ちゃんのこと(ry」って言ってたもの。  
>  My sister hates me. After all, a while ago she said "I don't li(skipped for
> brevity)"

or it could be for **emphasis** on a stand,

> 可愛いは正義なのだ!  
>  Cuteness is justice!

or when used with an interrogative, to express **wonder** or to ask for
explanation against somebody

> 妹のどこがいいのだ。うるさいし、かわいくないし、(ry  
>  What's so good about little sisters? They're rowdy, not cute, (skipped for
> brevity).
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answer
Derek’s answer gives a very accurate description of what のだから means, but let
me add a secondary point that is specific to your example: in this case, the
title _implies_ that in fact, the speaker likes her brother although the title
_states_ the opposite.

From Derek’s answer:

> お兄ちゃん sees his 妹's actions as signs that she might actually like him, but in
> reality that's not the case, so 妹 decides to set the record straight and
> make sure she and お兄ちゃん are on the same page with ～のだから (the implication
> being that お兄ちゃん should be well aware of this fact, but from 妹's
> perspective, he doesn't seem to be fully appreciative of it).

All of this is from the sister’s perspective. But the very need of setting the
record straight and making sure that she does not particularly like him _is_ a
sign that she actually likes him. Otherwise why would the brother think that
his sister likes him in the first place?

Denying explicitly and strongly that the speaker likes the addressee while the
speaker actually likes the addressee is such a stereotypical situation
(probably mainly in comics) that there is a slang which describes the very
situation: ツンデレ.

(By the way, the correct title is [お兄ちゃんのこと **なんか**
ぜんぜん好きじゃないんだからねっ!!](http://ja.wikipedia.org/wiki/%E3%81%8A%E5%85%84%E3%81%A1%E3%82%83%E3%82%93%E3%81%AE%E3%81%93%E3%81%A8%E3%81%AA%E3%82%93%E3%81%8B%E3%81%9C%E3%82%93%E3%81%9C%E3%82%93%E5%A5%BD%E3%81%8D%E3%81%98%E3%82%83%E3%81%AA%E3%81%84%E3%82%93%E3%81%A0%E3%81%8B%E3%82%89%E3%81%AD%E3%81%A3!!)
This なんか means that the speaker does not think お兄ちゃんのこと as an important thing,
which strengthens the speaker’s denial of the fact that she likes her brother,
and again strengthens the actual implication that she actually likes him.)
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answer
Well my teacher taught us that there is not much meaning to 「んです」 then making
the short form lighter in style. According to his researches on an academic
level there is no explanation to it more than a stylistic one.
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