does "ii janai" break the grammar?

[sodapple]

mina san:

well the grammar says "ii" is an "irregular i adjective" but why is conjugated as a "na adjective" yokunai it should be the correct conjugation... right?
then can I use desu, deshita, janai etc.. whit i adjs. ? I'm confused...

arigatou gozaimasu.

[QuackingShoe]

http://www.japanesepod101.com/forum/vie ... php?t=3596
You've always been able to use 'desu' with -i adjectives. That's how you make them polite. Otherwise, though, no, you do not use the copula with -i adjectives. This 'ja nai' is a special case that works differently.