Emoni said:
In Genki na kodomo, genki is a "Na adjective" and na is needed to connect the words unlike "i adjectives" like ookii. Na infact, is a form of Desu/Da. However, sometimes particals can be dropped, hence why you might have seen genki kodomo.
This explanation is pretty much correct, in that this "na" is used to connect "na-adjectives"/"na-nominals"/形容動詞（けいようどうし） to nouns, and is generally considered to be a form of the copula da/desu. I'm not sure where you heard that it can be dropped, though, as I'm fairly certain that constructions like "genki kodomo" or "kirei hito" would be perceived by native speakers as outright ungrammatical.
Emoni said:
As for Kirei na on their own. Na is used in the way "ne" is used when commenting to yourself. Kirei ne! Would translate to "That is pretty isn't it!" where Kirei na... Would translate to "Hmmm I think that is pretty."
I think you're kind of on the right track here, although I think "Hmmm I think" sounds too much like there's deliberation involved, when "kirei da na" is more likely to be a spontaneous reaction, a kind of self-directed "Man/Wow, it's (or 'she's', or whatever, depending on the context) beautiful..." Another point worth making, though, is that for both of these you can also get "kirei
da ne(e)" and "kirei
da na(a)", and the alternates with "da" in fact would probably be heard more often. I believe that when the 'da' is dropped, it's often characteristic of "gentle"/feminine-style speech), but I think for many speakers (and especially in the case of the self-directed "...naa") you're more likely to hear the alternate with
da.
kisu said:
So If I were commenting to myself or telling someone else that i though something was pretty i'd say "kirei na"?
Again, this is oversimplified, but I would say that if you were commenting to yourself, you'd probably say "kirei da na(a)..." and if you were remarking to someone else, you would say "kirei da ne(e)" (again, this is casual/direct-style; the polite alternate would be 'kirei desu ne(e)")
Keiichi said:
Stutz said:
Also, you can use na after the dictionary form of a verb to make the setence negative. I think that function is used only in informal speech though since it does come off as sort of crude in formal speech.
Hmm, I've never heard of that. Unless it's a shortcut or something. Are you sure you're not talking about "nai"?
Anyone can confirm?
It doesn't make the whole sentence negative, it makes the verb into a (extremely blunt and direct) negative imperative (command form), e.g. "
Ugoku na!" = Don't move! (or "Freeze!") Of course, this is yet another completely different
na from the other two above.
Keiichi said:
I see "zu" used as negative verbs (though not often at the end of a sentence): nenai = nezu = will not sleep
Maybe in classical Japanese the "zu" ending was a basic negative ending, but in the modern language it's much more often used (often in combination with "ni") to express "without doing (something)", i.e. "Kinou wa hotondo nezu ni benkyou shite imasita." (Yesterday I studied almost entirely without sleeping.)
I hope this helps to clear some things up -- hopefully someone more knowledgeable will step in to correct me if I've made any oversights.
(Oops -- it looks like Paul already cleared up the negative-imperative "na" while I was typing this wordy mess of a post. Sorry about that!)