な Adjectives

In Japanese, na-adjectives are words that are usually turned into attributive adjectives by adding a na な after them. Some na-adjectives are always classified as adjectives, but others can be classified as nouns or adverbs when they don't have the na.

The term for "na-adjective" in Japanese is na-keyoushi ナ形容詞, abbreviated na-kei ナ形. They're also confusingly called "adjectival nouns" in English and "adjectival verbs" in Japanese, keiyou-doushi 形容動詞, abbreviated keidou 形動.

• Relationship with Copulas
• Conjugation
• Chart
• Grammar
• Attributive Form
• Predicative Form
• Attributive Copula Na な
• What We Can't Turn Into a Na-Adjective?
• Negative Form
• でない vs. ではない
• Negative Past, etc.
• Past Form
• Te-Form
• Adverbial Form
• Adverbial Copula Ni に
• Ni Naru になる
• Suffixes That Are Na-Adjectives
• You da, You na, You ni
• Sou da, Sou na, Sou ni
• Teki da, Teki na, Teki ni
• Origins

Relationship with Copulas

Before starting the real article, allow me to offer a summarized version of how na-adjectives work. If you don't understand something written in this section, rest assured it's explained in excruciating detail in the grammar section below.

The na particle that comes after na adjectives is the attributive copula na な. Besides it, there's the predicative copula da だ. The adverbial copula ni に. And the te-form of the da copula, which's de で.

Anything that's related to na-adjectives is just switching one copula for another copula.

And there's more: na-adjectives are considered to be adjectives, so they can't fit the role of a noun grammatically. However, the copulas na, ni, da, de can be used with nouns and noun phrases that aren't classified as na-adjectives.

That means, for example, that you can say neko na hito 猫な人, "a person who is a cat," even though neko isn't classified as a na-adjective. A lot of the grammar valid for na-adjectives is also valid for nouns and noun phrases.

Conjugation

Since na-adjectives are just words with a na added after them, there's no way to conjugate or inflect the na-adjective itself, like you'd be able to do with the true adjectives, the i-adjectives.

However, mostly everything you can do with an i-adjective you can do with a na-adjective, except not through inflection, through changing the na particle for something else instead.

For reference, na-adjective equivalents of i-adjective inflections:

• subarashii 素晴らしい
  Splendid. (i-adjective.)
• migoto 見事
  Magnificent. (na-adjective.)

• Predicative form. (shuushikei 終止形)
• X ga subarashii ◯が素晴らしい
  X is splendid.
• X ga migoto ◯が見事
  X is magnificent.
  (predicative doesn't need na な!)
• Attributive form. (rentaikei 連体形)
• subarashii X 素晴らしい◯
  A splendid X.
• migoto na X 見事な◯
  A magnificent X.
• Predicative past form.
• X ga subarashikatta ◯が素晴らしかった
  X was splendid.
• X ga migoto datta ◯が見事だった
  X was magnificent.
• Attributive past form.
• subarashikatta X 素晴らしかった◯
  An X that was splendid.
• migoto datta X 見事だった◯
  An X that was magnificent.
• Predicative negative form.
• X ga subarashikunai ◯が素晴らしくない
  X isn't splendid.
• X ga migoto janai ◯が見事じゃない
  X ga migoto dewanai ◯が見事ではない
  X isn't magnificent.
• Attributive negative form.
• subarashikunai X 素晴らしくない◯
  An X that isn't splendid.
• migoto denai X 見事でない◯
  An X that isn't magnificent.
• Te-form.
• subarashikute 素晴らしくて
  Splendid and...
• migoto de 見事で
  Magnificent and...
• Adverbial form.
• subarashiku odoru ◯が素晴らしく踊る
  To dance splendidly.
• migoto ni odoru ◯が見事に踊る
  To dance magnificently.
• Naru-form.
• subarashiku naru ◯が素晴らしくなる
  Will become splendid.
• migoto ni naru ◯が見事になる
  Will become magnificent.
• Sa-form
• subarashisa 素晴らしさ
  Splendid-ness.
• migoto sa 見事さ
  Magnificent-ness.
• Suffix: sou.
• subarashisou 素晴らしそう
  Seems splendid.
• migoto sou 見事そう
  Seems magnificent.

Chart

For reference, a chart with na-adjective inflections.

Grammar

The grammar behind na-adjectives is 300% reliant on the Japanese copula, desu です, or rather, on the Japanese copulas, like, more than one of them.

There's even a book that talks only about them: The Japanese Copula: Forms and Functions.

But it's made for linguists, and I'm no linguist, I assume you're no linguist either, we aren't linguists, so let's go to what matters: how na-adjectives work in practice.

Attributive Form

Let's start with the attributive form, which is the form that gives na-adjectives their name: na-adjectives, because of the na they get when they're put into the attributive form.

Like all adjectives in Japanese, na-adjectives are pre-nominal: they come before nouns. See:

• kawaii neko 可愛い猫
  Cute cat.
  (this is an i-adjective.)
• yuumei na neko 有名な猫
  Famous cat.
  (now this is a na-adjective.)

You may have noticed that kawaii 可愛い, "cute," has the i い okurigana, while yuumei 有名, "famous," has no okurigana, is written entirely with kanji, and separately gets the na な particle.

This might mislead you into thinking the difference between i-adjectives and na-adjectives is that one has okurigana and the other doesn't. That isn't true; na-adjectives can have okurigana too:

• shizuka 静か
  Quiet.
• shizuka na neko 静かな猫
  Quiet cat.

Worse yet, they can even have i い as okurigana:

• kirai na neko 嫌いな猫
  Despised cat. Hated cat. Disliked cat.
  A cat [I] hate.

In the case above, with the word kirai 嫌い, there's a reason for this: kirai 嫌い is the connective form, ren'youkei 連用形, of the less common verb kirau 嫌う, "to hate." Similarly, suki 好き is the ren'youkei of the less common verb suku 好く, "to like."

• suki na neko 好きな猫
  Liked cat.
  A cat [I] like.

Predicative Form

Next we have the predicative form. In Japanese, the ga が particle marks the subject of a sentence, and everything that's not the subject is the predicate. See:

• neko ga yuumei 猫が有名
  Cats [are] famous.
  The cat [is] famous.

As always, the casual copula da だ and the polite copula desu です are optional, and pretty much don't change the meaning, just add nuance.

• neko ga yuumei da 猫が有名だ
  neko ga yuumei desu 猫が有名です
  Cats are famous.
  The cat is famous.

Furthermore, Japanese prefers to talk about the topic, with the topic marker particle wa は, rather than to talk about what the subject is or is doing. And both subject and topic can be implicit from context. For example:

• suki da 好きだ
  [It] is liked. (literally.)
  [I like it.] (how you'd translate it to English.)
• neko wa suki da 猫は好きだ
  As for cats, it is liked. (literally.)
• The above can mean two different things depending on context:
1. To someone, dogs or other animals are not liked, but cats are liked.
   That is, he might not like dogs, but he does like cats.
2. Something isn't liked by dogs or other animals, but to cats, it's liked.
   That is, dogs might not like it, but cats do like it.

Now, you may have noticed there's a huge, immense, immeasurable difference between the attributive form and the predicative form of na-adjectives.

THERE IS NO NA IN THE PREDICATIVE FOOOORMMMMmmm!!1111

Like WHAT?! It's a na-adjective! It's an adjective with a na! How can... how can there possibly be a na-adjective without a na? That's literally the thing that makes na-adjetives na-adjectives! Without a na na-adjectives are just plain na-less adjectives! WHAT'S GOING ON HERE?!?!?!?

But yeah, that's right. You don't add the na な particle after na-adjectives in the predicative form. If you do add it, it won't be the same particle. It'll be a different na particle that you put at the end of phrases to say "isn't it?"

• neko ga yuumei na? 猫が有名な？
  Cats [are] famous, [aren't they]?

To make sense of this, of why na adjectives don't have na in the predicative form, we'll have to understand why do we need the na な particle in the attributive form in first place.

Attributive Copula Na な

The na of na-adjectives is actually a copula. The prenominal copula, or attributive copula.

Basically, da だ is the copula you use in an independent clause, while na な is the copula you use in an attributive clause, also called adjectival clause. A clause that describes nouns.

(adjective clauses are also called "relative clauses." In Japanese, when you have a verb right before a noun, you have a relative clause. It's just that in this case the verb is the copulative verb.)

To have a better idea:

• neko ga yuumei da 猫が有名だ
  Cats are famous.
• yuumei na neko 有名な猫
  Famous cats.

It's boils down to na な being the attributive equivalent of da だ.

• If you can say:
  Noun ga something da.
• Then you can say:
  Something na noun.

So that's where na-adjectives come from, and it's why na-adjectives look like they can be basically any kind of word. Anything you can put a da on you can put a na on, at least grammatically speaking.

For example:

• jouhou ga tashika da 情報が確かだ
  The information is correct.
• tashika na jouhou 確かな情報
  Correct information.
  Information that is correct.
• kuni ga heiwa da 国が平和だ
  The country is peaceful.
• heiwa na kuni 平和な国
  Peaceful country.
  A country that is peaceful.
• yarikata ga samazama da やり方が様々だ
  Ways to do [it] are various.
• samazama na yarikata 様々なやり方
  Various ways to do [it].

Although grammatically speaking it's always correct, that doesn't mean it's always natural, makes sense, or is something you'd ever say. For example:

• kimyou na bouken 奇妙な冒険
  Bizarre adventure.
  An adventure that is bizarre.
  (you'd say this.)
• bouken ga kimyou da 冒険が奇妙だ
  Adventure is bizarre.
  (you wouldn't say this.)

Conversely, some stuff you'd think doesn't make sense actually makes sense in Japanese. Like putting na-adjectives before personal pronouns.

• boku ga tensai da 僕が天才だ
  I am a genius.
• tensai na boku 天才な僕
  Genius... I? Genius me?
  The me that is a genius?
• watashi ga dame da 私がダメだ
  I am useless.
• Dame na Watashi ni Koishite Kudasai ダメな私に恋してください
  Please Love the Useless Me.
• Title of a romance manga.
• kono machi ga daisuki da この街が大好きだ
  This town is very much liked. (literally.)
  [I love] this town.
• daisuki na kono machi 大好きなこの街
  Very much liked this town.
  This town that [I love].
• By the way, daisuki na kono machi de 大好きなこの街で, "in this city I love," is a song. ^{[Colorful Palette - youtube.com, 2018-11-03]}

Even more, transforming the predicative da into an attributive na isn't restricted to single words. You can turn a whole predicate into an adjective.

• kimi wa warui hito ga suki da 君は悪い人が好きだ
  About you: bad people are liked. (very literally.)
  You [like] bad people.
• Warui Hito ga Suki na Kimi e 悪い人が好きな君へ
  To the you who [likes] bad people.
• Title of a song. ^{[必殺エモモモモ!!「悪い人が好きな君へ」MV full - youtube.com, 2018-11-03]}

What We Can't Turn Into a Na-Adjective?

As you've seen above, you can add a na particle to basically anything, which means, in practice, that you can turn basically anything into a na-adjective. But is there something we can't turn into a na-adjective?

I mean, if you check a dictionary, you'll see that a lot of words are tagged as "na-adjectives." Those are words that are often used as na-adjectives. Some of them are literally adjectives, but some of them are nouns, others are adverbs, because, again, you can make anything into a na-adjective.

For example, the word for "cat," neko 猫, is totally not a na-adjective. It's a noun, clearly. But you can turn it into a na-adjective nonetheless if you have a situation specific enough. For example, say you are a cat.

• watashi wa neko da 私は猫だ
  I'm a cat.
• neko na watashi 猫な私
  The me that is a cat.

So you can turn even neko into a na-adjective. Except that doesn't happen normally, so a dictionary won't waste its time saying every word out there may technically be a na-adjective.

But is there anything we grammatically can't turn into a na-adjective? Yes. There is.

The pattern that has followed us so far is: if you can add a da to it, you can add a na to it. Therefore, if you can't add a da to it, you can't add a na to it.

For example, you can't add a da to an i-adjective, at least not directly. To add the da, you need the nominalizing no の particle or its n ん contraction between the two.

• neko ga kawaii da 猫が可愛いだ
  (wrong.)
• neko ga kawaii-n-da 猫が可愛いんだ
  neko ga kawaii no da 猫が可愛いのだ
  Cats are cute.

Similarly, you can't put a da after a verb. You need the nominalizing no particle in this case too.

• sakana ga oyogu da 魚が泳ぐだ
  (wrong.)
• sakana ga oyogu-n-da 魚が泳ぐんだ
  sakana ga oyogu no da 魚が泳ぐのだ
  Fishes swim.

The phrases above, despite having da, can't be converted to attributive na. You can't say no na のな. This is because you don't need those particles to begin with. You can put verbs and i-adjectives directly before nouns without the need of the na particle, and they'll qualify that noun just fine.

• kawaii no na neko 可愛いのな猫
  (wrong.)
• kawaii neko 可愛い猫
  Cute cat.
• oyogu no na sakana 泳ぐのな魚
  (wrong.)
• oyogu saka 泳ぐ魚
  Fish that swims. [Swimming] fish.

Also note that if you put a na な after a verb, at the end of a sentence, it's a different na な that means "don't!" instead and has nothing to do with adjectives.

• oyogu na! 泳ぐな！
  Don't swim!

Furthermore, although you can technically turn any noun into a na-adjective, usually nouns become no-adjectives instead. That is, they get the no の particle, not the na な particle.

• neko na watashi 猫な私
  The me that is a cat. (technically correct version you wouldn't use.)
• neko no watashi 猫の私
  The me that is a cat. (version you'd normally use.)

Beware that a lot of words are listed in dictionaries as both nouns and na-adjectives, so sometimes they take na, other times they take no. For example:

• ninki na manga 人気な漫画
  Popular manga.
• ninki no geemu 人気のゲーム
  Popular game.

Negative Form

The negative form of na-adjectives is literally just replacing the normal copula by a negative copula such as denai でない, dewanai ではない or its contraction, janai じゃない.

• kiken na ninmu 危険な任務
  Dangerous mission.
  Mission that is dangerous.
• kiken denai ninmu 危険でない任務
  kiken dewanai ninmu 危険ではない任務
  kiken janai ninmu 危険じゃない任務
  Not dangerous mission.
  Mission that is not dangerous.

In modern Japanese, when the adjective is attributive like above, you'd use denai でない, and when the adjective is predicative like below, you'd use dewanai ではない or janai じゃない. ^{[「～でない」と「～ではない」とどう違いますか？ - detail.chiebukuro.yahoo.co.jp, 2018-11-03]}

• kono ninmu ga kiken da この任務が危険だ
  This mission is dangerous.
• kono ninmu ga kiken janai この任務が危険じゃない
  This mission is not dangerous.

でない vs. ではない

The word janai, or rather, dewanai ではない, is the combination of the particle de で, the particle wa は, and the auxiliary adjective nai ない.

The difference between denai and dewanai is obviously this wa は particle. It has a contrastive function. Basically, it means "I don't know about other cases, but this specific case is [something]."

Since we also got a negative nai ない there, it means "this specific case is not [something]."

In the predicative, this "this specific case" nuance is important because you're saying "this thing I'm talking about is specifically not true." Another way to understand this is assuming that janai and dewanai deny the whole phrase, rather than just the adjective.

In the attributive, however, that nuance is often unnecessary, which's why denai is normally used in the attributive while dewanai is used in the predicative.

• ninmu ga kiken dewanai 任務が危険ではない
  The mission, dangerous, it is not. (it could be something else, though.)
  It is not a dangerous mission. (it's something else.)
• kiken dewanai ninmu 危険ではない任務
  A mission that, dangerous, it is not. (but could be something else.)
  A mission that's not dangerous. (it's something else, but not dangerous.)
• kiken denai ninmu 危険でない任務
  A non-dangerous mission. (since this doesn't have a wa, it doesn't emphasize contrast.)

If the phrase is simple enough, it makes more sense to use a simple na-adjective in the attributive with a negative copula denying the whole phrase (janai, dewanai). You'd only use denai if your noun phrase (kiken denai ninmu) is part of the bigger phrase.

• {kiken na ninmu} dewanai 危険な任務ではない
  {kiken na ninmu} janai 危険な任務じゃない
  It's not {a dangerous mission.} (it's something else, a safe mission, presumably.)
• {kiken denai ninmu} nante nai-n-da 危険でない任務なんてないんだ
  There's no such thing as a {non-dangerous mission}.

Past Negative, Adverbial Negative, Etc.

As always, the nai ない auxiliary can be inflected as an i-adjective.

• denakatta でなかった
  dewanakatta ではなかった
  Past negative.
• denaku でなく
  dewanaku ではなく
  Adverbial negative.
• denakute でなくて
  dewanakute ではなくて
  Te-form.

Past Form

The past form of na-adjectives is literally just placing the normal copula by a past copula such as datta だった.

• heiwa na kuni 平和な国
  Peaceful country.
• heiwa datta kuni 平和だった国
  Was peaceful country.
  Country that was peaceful.

Again, you can put datta instead of na in the attributive because you can but datta instead of da in the predicative.

• kono kuni ga heiwa da この国が平和だ
  This country is peaceful.
• kono kuni ga heiwa datta この国が平和だった
  This country was peaceful.

If you're just saying something was adjective, it makes more sense to use an attributive adjective in the non-past (with na) and add a predicative copula in the past at the end of the sentence.

• heiwa na kuni datta 平和な国だった
  [It] was a peaceful country.

So you'd only use datta in the attributive if it's a more complicated phrase.

• heiwa datta kuni wo sensou ni makikomu 平和だった国を戦争に巻き込む
  To drag into war the country that was peaceful.
  To drag into war an [once] peaceful country.

Te-Form

The te-form of na-adjectives is literally just replacing the normal copula by the de で part... wait, no, by the de で that's actually the te-form of the copulative verb da!!!

That's right. As extremely confusing as it sounds, and is, there are two de's in Japanese: the de で particle that creates adverbs, and the de で that's the te-form of the copula da だ.

(more confusingly yet, they're etymologically the same thing since da is the abbreviation of de aru である, but let's ignore this for the sake of our sanity.)

Let's begin with the de that's the te-form of da.

As explained in the article about i-adjectives, adjectives can be connected to other adjectives through their te-forms. The te-form of i-adjectives is -kute ～くて.

• kirei na hito 綺麗な人
  Pretty person.
• yasashii hito 優しい人
  Kind person.
  Gentle person.
• yasashikute kirei na hito 優しくて綺麗な人
  A person that is kind and pretty.

The last adjective of a te-form chain shouldn't be in the te-form but in the attributive form, -i ～い ending for i-adjectives, na copula for na-adjectives.

For example, above the na-adjective kirei was the last adjective before the noun hito, that's why it was kirei na. If we switch the adjectives' positions, the adverbial yasashikute will return to its attributive form yasashii, while kirei na will become kirei de:

• kirei de yasashii hito 綺麗で優しい人
  A person that is pretty and kind.

In the predicative you don't need the na, just like it would be without two adjectives connected by te-form.

• kanojo ga kirei de yasashii 彼女が綺麗で優しい
  kanojo ga kirei de yasashii-n-da 彼女が綺麗で優しいんだ
  She is pretty and kind.
• kanojo ga yasashikute kirei 彼女が優しくて綺麗
  kanojo ga yasashikute kirei da 彼女が優しくて綺麗だ
  She is kind and pretty.

Although there's no hard rule regarding the order of the adjectives, it's sometimes implied the first adjective may cause the second. So there are things you'd say in one order you wouldn't say in another order.

• shoshinsha de heta na watashi 初心者で下手な私
  The me that is a beginner and unskilled.
• That is: because I'm a beginner, I'm also unskilled.
• heta de shoshinsha na watashi 下手で初心者な私
  The me that is unskilled and a beginner.
• That is: because I'm unskilled, I'm also a beginner.
• This doesn't make as much sense as the one above, so you probably wouldn't say it like this.

For reference, an example of the de で particle that's not the te-form of the copula:

• geemu de asobu ゲームで遊ぶ
  To play by game.
  To play with a video-game.

Adverbial Form

The adverbial form of na-adjectives is literally just replacing the normal copula by the ni に particle, which some scholars analyze as the "adverbial copula." So, to recap:

• Predicative copula da だ
• kono machi ga shizuka da この街が静かだ
  This town is quiet.
• Attributive copula na な
• shizuka na machi 静かな街
  Quiet town.
• Adverbial copula ni に
• shizuka ni nemuru 静かに眠る
  To quietly sleep.

As you can see, despite the scary "adverbial copula" term, this is all pretty easy. It's basically -ly in English.

• hontou na shi 本当な死
  Real death.
• hontou ni shinda 本当に死んだ
  Really died.
• seikaku na kotae 正確な答え
  Correct answer.
• seikaku ni kotaeru 正確に答える
  To correctly answer.
  To answer correctly.

The only problem is that there's a lot of disparity between English and Japanese, so the literal translation may not sound natural, or even doesn't express the same message it does in Japanese.

This results in a na-adjective having different translation when it's used as an adjective versus when it's used as an adverb. For example:

• massugu na seikaku まっすぐな性格
  A "straight" personality. (straight as in "right," "direct.")
  A [honest] character. (someone of honest character doesn't lie.)
• massugu ni arukenai まっすぐに歩けない
  Straightly walk able not. (negative potential of aruku 歩く)
  Can't walk straight.
• tokubetsu na oshie 特別な教え
  A special teaching.
• tokubetsu ni oshiete ageru 特別に教えてあげる
  To teach [you] specially. To tell [you] specially.
  [I'll do you a favor and] tell [you.]
  [I'll] tell [you only because it's you.]

Adverbial Copula Ni に

The term "adverbial copula," abbreviated in books as COP-ADV, might elude you a bit. And by a bit I mean a lot. After all it's two terms that sound too complicated. So, here, I'll try to explain what an adverbial copula is.

First off, a copula is also called a copulative verb. If it's called a copulative verb, then, naturally, a copula is a verb. And if it's a verb, you can assume it works like just any other verb.

Except it doesn't.

At least not in Japanese.

To understand why, let's see an example of a normal verb in action:

• shiro ga ugoku 城が動く
  The castle moves.
• ugoku shiro 動く城
  The castle that moves.

Above we have the verb ugoku, "to move." In the first example, it's the verb of a simple clause. In the second example, it's the verb of a subordinate adjectival clause. That is, a separate clause, "that moves," serving as adjective, describing the "castle" noun.

In English, we often use subordinating prepositions like "that" and "who" to introduce these clauses. Japanese doesn't have those, so the verb comes right before the noun. Because of this, it might look like there isn't a separate clause there, but there is:

• {ugoku} shiro ga ugoku 動く城が動く
  The castle {that moves} moves.
• In bold: main clause.
• In curly brackets: subordinate adjectival clause.

(by the way, particles can be called postpositions, since they come after stuff, oppositely to prepositions, that come before stuff.)

Now, the thing about clauses is that you can only have one verb per clause. And a copula is a verb. So every time there's a copula, there's a clause, just like above.

And yet, we can't do this:

• kuni ga heiwa da 国が平和だ
  The country is peaceful.
• heiwa da kuni 平和だ国
  The country that is peaceful. (wrong!!!)

That's because these pesky Japanese copulas are different from the regular Japanese verbs.

A regular verb doesn't care if it's in the main clause or in a subordinate clause. The ugoku above remained ugoku in both cases. But copulas care. The Japanese copula must match the type of clause they're verb for.

• heiwa da 平和だ
  This is a independent clause.
• heiwa na 平和な
  This is an adjectival clause, also called attributive clause.
• heiwa ni 平和に
  This is an adverbial clause.

So that's why it's an "adverbial copula."

This is a bit hard to get because of the implication: it implies your average Japanese sentence has way more clauses than you'd expect. For example:

• {{shizuka na} neko ga {shizuka ni} nemuru no} da 静かな猫が静かに眠るのだ
  The quiet cat sleeps quietly.

The English translation "the quiet cat sleeps quietly" has just one clause. After all, "quiet" is an adjective, "quietly" is an adverb, and they don't need clauses. The only verb we got is "sleeps," and since it's only one verb, we only have one clause.

By contrast, shizuka na neko ga shizuka ni nemuru no da has the verb nemuru plus three copulas, na, ni, and da. Since each copula is a verb, that means we have four verbs in total, which means four clauses. That's a lot of clauses.

If we were to translate to English keeping the same number of clauses, we'd have to say some monstrosity like this:

• {The cat {that is quiet} sleeps in a way {that is quiet}}, it is.
  Is, sleeps, is, is. Four clauses.

Maybe because it's so clausy and na-adjectives end up becoming mere single-word clauses anyway, some grammars prefer to analyze them not as clauses with a na copula that can be inflected, but as adjectives with a na suffix that can be inflected.

(as you may have realized, this article is based on the clause analysis, not the suffix analysis. Because I just found out about it so it's more interesting to me.)

Now, remember that in Japanese na-adjectives are called "adjectival verbs," keiyou-doushi 形容動詞?

If they're verbs they need their own clauses. Since some grammars disagree with na introducing a new clause every time, they couldn't call them "verbs." That's probably why in English the term "adjectival noun" exists to to refer to them instead.

Ni Naru になる

The construction ni naru になる is the verb naru なる, "to become," preceded by the adverbial copula ni に. Basically, X-ni-naru means "to become X."

Now, this is an interesting construction because it validates a lot of this copula stuff.

Like I said before, you can make (mostly) everything a na-adjective. Because na is a copula, so anything that can take da can take na. And the adverbial form of na-adjectives replaces the adjectival copula na by the adverbial copula ni.

So when we say:

• heiwa ni naru 平和になる
  To become peaceful.

We're actually saying:

• heiwa ni naru 平和になる
  To peaceful-ly become.
  To become in a way {that is peaceful.}

This might sound weird to you if you already know that the ni に particle can be used to mark the indirect object of a phrase, like this:

• kimi ni ninjutsu wo oshieru 君に忍術を教える
  To teach ninja-arts to you.

And like always you can be very implicit in Japanese, so you don't need to explicitly say the direct object if it's implied by context:

• kimi ni oshieru 君に教える
  To teach [something implicit] to you.

So you might look at this noun-ni-verb construction and conclude that noun-ni-naru is the same thing. That naru is a verb that takes an indirect object marked by the ni particle, just like oshieru above.

• neko ni naru 猫になる
  To become a cat.
• A cat - indirect object???

BUT THAT IS WRONG!!!

The ni of ni naru is not the indirect object marker!!!

It's the adverbial copula!!!!111

• sonna baka na! そんなバカな！
  no wai — you, probably.

But yes, wai. And there's an easy way to confirm this is actually true and I'm not making stuff up: when we have an i-adjective, the construction is not ni naru, it's -ku naru ～くなる. This -ku is the adverbial form of i-adjectives.

• takai 高い
  High.
  Expensive.
• takaku tobu 高く飛う
  To jump high.
• takaku naru 高くなる
  To become high.
  To become expensive.

So, if with i-adjectives the verb naru is modified by the adverbial form, then, with na-adjectives, the verb naru must be modified by the adverbial form also!

• takaku naru 高くなる
  To become in a way {that is expensive.}
• neko ni naru 猫になる
  To become in a way {that is a cat.}

This can also be observed in the fact that anything you can say ending in a da copula you can say ending in ni naru, because ni is simply the adverbial variant of the da copula.

• anime ga suki da アニメが好きだ
  Anime is liked. (literally.)
  [I like] anime.
• anime ga suki ni naru アニメが好きになる
  To become in a way {that anime is liked.}
  To start liking anime.
• {{anime ga suki ni} natta} kikkake アニメが好きになったきかっけ
  The motive {to have become in a way {that anime is liked.}}
  The reason why [I] started liking anime.

Suffixes That Are Na-Adjectives

An important thing about na-adjectives are certain suffixes that are na-adjectives. Because they're awfully versatile and a mess to understand.

Such are words like you よう and sou そう. They always come after a phrase that describes them, and are used as adjectives or adverbs for other stuff.

You da, You na, You ni

Let's start understand you よう.

• tada no shikabane ただのしかばね
  Just a corpse.
• tada no shikabane no you da ただのしかばねのようだ
  [It] is the appearance of just a corpse. (literally.)
  [It seems to be] just a corpse.

As you can see above, you よう means literally "appearance." And it's always described by something that comes before it. It never shows up alone in a phrase. In English, this phrase becomes translated to "seems to be," "appears to be," "like," etc.

Since it's a na-adjective, you can have an attributive you na and an adverbial you ni too:

• shikabane no you na hito しかばねのような人
  A person that [seems to be] a corpse.
  A person [like] a corpse.
• shikabane no you ni ikiru しかばねのように生きる
  Living [like] a corpse.

By the way, the pronouns konna, sonna, anna, and donna work like abbreviations of kono/sono/ano/dono you na. However, they do not work like na-adjectives, and you can't say konni to say kono you ni. ^{[｢こんな｣ってどうして形容動詞なんですか？ - detail.chiebukuro.yahoo.co.jp, 2018-11-03]}

Sou da, Sou na, Sou ni

The sou そう suffix works the same way, except it implies something "might be" something because it "looks like" something. For example:

• oishii 美味しい
  Tasty.
• oishisou da 美味しそうだ
  [It] looks like it's tasty
  (we aren't sure if it really is, it just looks like it is.)
• oishisou na banana 美味しそうなバナナ
  A tasty-looking banana.
• oishisou ni taberu 美味しそうに食べる.
  To eat in a way {that is tasty-looking.)

Teki da, Teki na, Teki ni

Another common na-adjective suffix is teki 的.

• rekishi 歴史
  History.
• rekishi-teki 歴史的
  Historical.
• kore wa rekishi-teki da これは歴史的だ
  This is historical. (a historical event, for example.)
• rekishi-teki na shashin 歴史的な写真
  A historical photo.
• rekishi-teki ni yuumei na hito 歴史的に有名な人
  A person who is historically famous.

Origins

Lastly, one thing that's not really useful but it's cool to know is the origin of na-adjectives.

The na copula of na adjectives comes from the construction ni aru にある. This is similar to how the da copula comes from de aru である.

1. heiwa ni aru kuni 平和にある国
   (say this fast)
2. heiwa naru kuni 平和なる国
   (drop the ru)
3. heiwa na kuni 平和な国
   Peaceful country.

The aru ある of ni aru and de aru is the verb for "to exist," aru 在る.

In modern Japanese, de aru である has been analyzed as a predicative copula de で plus a dummy copula aru ある. ^{[Adjectives and the Copulas in Japanese, by Kunio Nishiyama, published in 1999]}

In other words, this aru isn't a verb with the meaning of "to exist" anymore, it's only there to serve a syntactical purpose, to do something related to the Japanese grammar syntax.

That is, you can't inflect the de directly like other u-ending verbs or i-ending adjectives, but you can inflect aru to past form, te-form, etc. So the inflection of the dummy aru serves as the inflection of the copula for grammatical purposes.

• heiwa de aru 平和である
  heiwa da 平和だ
  heiwa de arimasu 平和であります
  heiwa desu 平和です
  To exist in peace. (wrong!)
  To be in peace. (right.)
• heiwa de atta 平和であった
  heiwa datta 平和だった
  heiwa dearimashita 平和でありました
  heiwa deshita 平和でした
  Existed in peace. (wrong!)
  Was in peace. (right.)

Besides ni aru and de aru, there was also a third construction, to aru とある.

Some adverbs in Japanese take the to と particle. By adding aru ある, it turns those adverbs into adjectives.

So, to aru and ni aru adjectives became taru adjectives and naru adjectives, and then naru adjectives became na adjectives.

And you can actually add taru and naru to such words and conjugate that. It's the so-called tari-katsuyou タリ活用 and nari-katsuyou ナリ活用.

• doudou to furumau 堂々と振る舞う
  To behave majestically.
• doudou toaru sugata 堂々とある姿
  doudou taru sugata 堂々たる姿
  Majestic form. Majestic appearance.
• shizuka naru Don 静かなるドン
  The Don that is quiet.
• Title of a manga.

In modern Japanese, this taru たる is considered to be overly polite (since it's usually found in classical Japanese.)

You can still find taru in some manga, but then the meaning is closer to "[something] which's supposed to be [something]" rather than "[something] which is [something]."

Manga: "Black Butler," Kuroshitsuji 黒執事

• Fantomuhaibu-ke no
  shitsuji taru mono
  ファントムハイブ家の執事たるもの
  [Someone] who's supposed to be the butler of the Phantomhive's family...
• mono もの
  A person.
  [Someone who...] (when qualified by an adjective.)
  (note about homonyms: mono 者 is person, mono 物 is thing.)
• kono teido no waza ga
  tsukaenakute
  この程度の技が　使えなくて
  ...not able to use a technique of this level...
• tsukaenakute 使えなくて
  (te-form of)
• tsukaenai 使えない
  Not able to use.
  (negative form of)
• tsukaeru 使える
  Able to use.
  (potential form of)
• tsukau 使う
  To use.
• doushimasu
  どうします
  ....does what? (this is an expression.)
• (potential negative) +
  dou suru どうする
  If you aren't able to [something] what are you going to do?
• This is a rhetorical question. It implies that being able to [something] is natural, and if you can't, there's something fundamentally wrong.
• If a surgeon can't operate, what is he going do? Answer: nothing. He isn't a surgeon then!
• If someone who's supposed to be a Phantomhive's butler can't even use a technique of this level, what is he going to do? Nothing! He isn't a Phantonhive's butler then!