While watching a show I heard the word 理想 being used. From context, I finally got what the word 理想 meant, but, whilst talking to myself, I automatically attached な on to it. The thing that got me thinking, though, was the fact that the characters were using it in conjuction with の. At first I thought 理想 was an adjective. Rikaichan says its a noun.

So I wonder...

How do you know whether to use の or な in this manner? Is there some quality in the word that determines this? Where is the line between adjective and noun drawn?

I appreciate greatly any information on this subject.

What a great question, I would also like to hear if anyone has any insight about this.

My first reaction was too look it up in my electronic dictionary, which indeed says that 理想の is correct, but also lists 理想的（な）as another way of saying it. I honestly don't know how to define any difference between na-adjectives and nouns...though I guess technically it's the same in English, there's no "official" difference between a word like tall vs. animal. (the way there is with i-adjectives in Japanese, ie 高い vs 動物...but not 理想 vs 簡単...I hope that makes sense) I probably say things like "risou na" all the time without even thinking about it but from now on I bet I'll be more careful.

saritza Wrote:My first reaction was too look it up in my electronic dictionary, which indeed says that 理想の is correct, but also lists 理想的（な）

I think you found the answer!

So it seems to me that you have 3 choices:
1. Simple な-adjective like 素敵「な」
2. Noun + の like 理想の
3. Noun的 + な like 理想的な (this doesn't apply to all nouns - only certain ones)

I think I was sloppy, too, in using 理想な (wrong) - should be 理想の or 理想的な

Na-adjectives are usually abstract nouns (I love the oxymoron).
Problem is, the converse is not always true.

Maybe that's why it's easy to miscategorize 理想.

Yes, it is an interesting question. According to a colleague of mine, who is Japanese, and a bit of a linguist, there is no obvious rule on whether to use な or の when making a noun into an adjective. I can't find anything authoritative that discusses this in any detail. It may be just one of those things you have to learn on a case by case basis and look up if you are unsure.

And what about cases like 不断 which takes な or の according to the meaning?
不断の努力
不断な政治家

kazelee Wrote:Where is the line between adjective and noun drawn?

You might find it easier to think of words as having multiple possible uses (rather than being in only a single grammatical category), so in this case 理想 is both a noun and a の-adjective (to borrow EDICT's codes, "n, adj-no"). This is similar to the way that some but not all nouns can be turned into verbs by adding する. I think you just have to pick up the valid uses case-by-case...

The most overloaded word I found with a quick search was 色々, which is "n,adj-na,adj-no,adv,adv-to".

Case by case, huh? Rat's. I was hoping there would be some pattern of formula.

Thank you all very much, for you insight. Looks like it's time for me to dive into the dictionary again.

な adjectives use な, normal nouns do not. The problem is, there are actual の adjectives too, though they are kind of unusual.

This is a problem that gets solved from insight. I wouldn't worry about it too much. As you parse through more and more Japanese material you'll pick up a feeling for when to use each of these correctly. The annoying part is that with higher-level concepts like this there are usually very few wrong ways, lots of decent ways, and only a few perfect ways. The task is choosing the perfect one, but for getting your point across capably the decent ways will work most-often.

If you asked any of the Japanese the rhyme or reason behind it, they wouldn't know either. They just know one thing is said while another thing is said rarely or not at all. Remember, grammar is about language. It is not itself the language. Most language is a large set of idiomatic expressions. We can use grammar to simplify it a lot, but there doesn't exist any sort of definitive grammar formula to derive good Japanese. If we had such formulas then machine translation would work better than it does.

I have to admit, I've never understood the concept of "の-adjectives." Aren't all nouns* theoretically の-adjectives? Isn't that the very function of の? Is there more to it? Stupid question, maybe.

* assuming of course that な-adjective aren't considered nouns.