I think of だ as being the only copula, which can be inflected to で and な. In my mind all other copula-like words are derived from these forms, i.e. です ⇔ であります じゃない ⇔ ではない だろう ⇔ であろう etc. ...
Since there is possibility of "じゃありません" instead of "じゃないです" (which is logical, given "ありません" is polite "ない"), and it also seemed that I have seen "じゃ" used without "ない", I'd like to ask, what "じゃ" ...
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. ...
Specifically, in the expression 好きなんだ (I love you) why not just say 好きだ or 好きです?
I saw a sentence like "それ使ってるっす" and none of my dictionaries have an entry for just "っす". Is it a verb form, gobi, or something else?