Do adjectives/adjective-like verb forms in informal speech need a copula?


The class I go to uses the «Minna no Nihongo» textbook, and according to it
you can say the following in informal language:

> そのカレーライスおいしい？
>
> わたしは富士山にのぼりたい。

_(See book 1, lesson 20)_

So I gathered, the copula can be omitted in adjective-like predicates.
However, when I posted on Lang-8 applying the new-found knowledge, people
corrected me:

ドイツはいちども行ったことがないから、ずっと ~~行きたかった~~ **行きたかったんだ** or **行きたかったです** 。

Hence, the question: why だ／です is necessary here? What's the general rule?




I think the confusion arises because です can both replace だ as the copula
(行きたかったんです), or simply mark politeness (行きたかったです).

The correction you received has little to do with a grammatical need for だ or
です in a sentence, but rather the two improved versions sound more natural.

Grammatically speaking,

> ドイツはいちども行ったことがないから、ずっと行きたかった。

is perfectly fine.

You need a copula when you have a noun predicate. 行きたかったんだ needs だ because ん
nominalizes the preceding phrase. 行きたかった alone doesn't need a copula, but may
be marked with です for a more polite tone.

Your original sentence could be amended to

> ドイツはいちども行ったことがなかったから、ずっと行きたかった～  
>  I had never been to Germany and had been longing to go...

in which case you don't need んだ or です.




I think the confusion arises because です can both replace だ as the copula
(行きたかったんです), or simply mark politeness (行きたかったです).

The correction you received has little to do with a grammatical need for だ or
です in a sentence, but rather the two improved versions sound more natural.

Grammatically speaking,

> ドイツはいちども行ったことがないから、ずっと行きたかった。

is perfectly fine.

You need a copula when you have a noun predicate. 行きたかったんだ needs だ because ん
nominalizes the preceding phrase. 行きたかった alone doesn't need a copula, but may
be marked with です for a more polite tone.

Your original sentence could be amended to

> ドイツはいちども行ったことがなかったから、ずっと行きたかった～  
>  I had never been to Germany and had been longing to go...

in which case you don't need んだ or です.

