い Adjectives

An i-adjective is a type of Japanese adjective with a base form ending in -i ~い, like hayai 速い, "fast," kawaii 可愛い, "cute," tanoshii 楽しい, "fun," and so on.

In Japanese, such words are called keiyoushi 形容詞, "adjectives," or, more specifically, i-keiyoushi イ形容詞, abbreviated i-kei イ形.

The i-adjectives are different from other Japanese adjectives by the fact they're true adjectives: the word is an adjective as-is, it isn't a noun or adverb that needs a particle in order to be used as an adjective. (which is the case with na-adjectives and no-adjectives.)

Conjugation

The conjugation of i-adjectives in Japanese, or rather, the inflection of the i-adjectives in Japanese, because conjugation is for verbs-only, or even the declension of the i-adjectives, which is a word literally nobody knows that's for the inflection of adjectives, works as follows:

-i ～い
Base form.
-ku ～く
Adverbial form.
-katta ～かった
Past form.
-kunai ～くない
Negative form.
-kunakatta ~くなかった
Past negative form.
-ku naru ～くなる
"Will become" form.
-kute ～くて
Conjunctive form. Te-form.
-kereba ～ければ
Conditional form. Ba-form.
-kattara ～かったら
Past conditional form. Tara-form.
-sa ～さ
"-ness" form. Sa-form.
-sugiru ～すぎる
"Too much" form.
-sou ～そう
"Seems" form.
~kattari ～かったり
Tari-form.
-karou ～かろう
Volitional form.
-kare ～かれ
Imperative form.

Japanese Terms for Inflections

Note that the above is merely an useful reference. The actual, factual, technical, classification of i-adjectives "inflections,"katsuyou 活用, is far, far, far, FAAAAarrrrrrrrrrrr, more useless to anyone trying to learn Japanese. Behold:

mizenkei 未然形
-karo ～かろ
ren'youkei 連用形
-ka' ～かっ
-ku ～く
shuushikei 終止形
-i ～い
rentaikei 連体形
-i ～い
kateikei 仮定形
-kere ～けれ
meireikei 命令形
-kare ～かれ (archaic.)

Now, to make sense of this mess:

連体形 vs. 終止形

The rentaikei 連体形 and shuushikei 終止形 that look identical (kawaii vs. kawaii), but refer to two different things grammatically.

The rentaikei is when an adjective modifies something, like a noun, kawaii neko, and the shuushikei is when it's at the end of the sentence, like neko ga kawaii.

In English, the terms attributive adjectives and predicative adjectives would refer to how the rentaikei and shuushikei forms are used. ^{[Attributive and predicative adjectives - en.oxforddictionaries.com, 2018-10-25]}

Also, rentaikei is sometimes called the pre-nominal form or prepositive form. This is because pre-nominal adjectives are adjectives that come before nouns. For example:

nagai hito 長い人
Long person. Long people.
- Rentaikei, attributive adjective.
- Pre-nominal adjective, before noun "person," hito 人.
mimi ga nagai 耳が長い
Ears are long.
- Shuushikei, predicative adjective.
mimi ga nagai hito 耳が長い人
Person whose ears are long. (e.g. elves.)
- Rentaikei, attributive adjective.
- When the adjective is at the end of an adjectival clause, the form is still said to be rentaikei, not shuushikei.
mimi ga nagai kedo 耳が長いけど
The ears long people, but...
- Shuushikei, predicative adjective.
- When the adjective is before a conjunction, then it's predicative.

This is more obvious with na-adjectives.

kirei na hito
綺麗な人
A person that is pretty. (rentaikei)
kirei da kedo
綺麗だけど
Is pretty, but... (shuushikei)

Forms and Suffixes

Most inflections are a combination of one of the forms above plus a suffix or another.

-ka' ～かっ, the ren'youkei
- plus ta た auxiliary verb,
  = -katta ～かった, the past form.
- plus tara たら, the kateikei of the ta auxiliary.
  = -kattara ～かったら, a conditional form.
- plus tari たり, a particle
  = -kattari かったり, the tari form.
-kere ～けれ, the kateikei, plus ba ば
= -kereba ～ければ, the ba-form, a conditional form.
-ku ～く, the other ren'youkei,
- plus the auxiliary nai ない
  = kunai くない, negative form.
- inflecting this nai ない to its past form
  = kunakatta くなかった, past negative form.
- plus naru なる, the verb "to become,"
  = "will become adjective," in the future.
-karo ～かろ, the mizenkei, plus u う particle,
= -karou ～かろう, the volitional form.

As I'm no linguist, I can't tell for sure where an inflection really ends and where something else begins. As you are probably no linguist either, you probably don't care about it. What's important is you glue stuff to the adjective's stem and then it means stuff.

Stem

The "stem" of an i-adjective, gokan 語幹, is literally the i-adjective without the i it ends with. For example:

hayai 速い (base form)
haya 速 (stem.)
takai 高い (base form.)
taka 高 (stem.)
kawaii 可愛い (base form.)
kawai 可愛 (stem.)
utsukushii 美しい (base form.)
utsukushi 美し (stem.)

This word, "stem," means "root," in case English isn't your native language. All inflections of an adjective branch away from this root.

The stem of an i-adjective doesn't mean anything by itself. You can't even call it a word. What's important about it is that some suffixes are added directly to the stem to form other words. Like:

haya-sou 速そう
Seems fast.
haya-sa 速さ
Fast-ness.
haya-sugiru 速すぎる
Too fast.

Chart

For reference, a cheat-sheet containing the inflections of i-adjectives in Japanese.

Ending With I vs. I-Adjective

Although most words that end in i い are i-adjectives, not all words that end with i are i-adjectives.

For example, kirei きれい, "pretty," ends in i but is a na-adjective instead.

Usually, you can tell i-adjectives apart from words that just end with i because you can't inflect kanji, only kana. For example, kirei written with kanji is kirei 綺麗. There's no i い okurigana there; it can't be inflected; it's not an i-adjective.

utsukushii 美しい
Beautiful. (i-adjective.)
kirei 綺麗
Pretty. (na-adjective.)
sensei 先生
Teacher. (noun.)

Note that sometimes a word has an i い ending written in okurigana and still isn't a an i-adjective.

kirai 嫌い
Detestable. (i-adjective.)

In the case above, it happens because kirai 嫌い is a conjugation of the verb kirau 嫌う, "to detest," thus kirai na 嫌いな describes something you detest. (similarly, suki 好き comes from suku 好く.)

Grammar

Attributive Form

Like other Japanese adjectives, i-adjectives can modify whatever noun comes after them, which is similar to how adjectives work in English. For example:

kawaii neko 可愛い猫
Cute cat.

An adjective that modifies a noun this way is called an attributive adjective. In Japanese, the form is called rentaikei 連体形.

Inflections of i-adjectives sometimes need to be translated as adjectival clauses instead of simple adjectives in order to make sense in English. .

kawaikunai neko 可愛くない猫
Not-cute cat.
A cat that's not cute. (clause.)
atsukatta natsu 暑かった夏
Was-hot summer.
The summer that was hot.
samukunakatta fuyu 寒くなかった冬
Was-not-cold winter.
The winter that was not cold.

Predicative Form

Like other adjectives, the i-adjective can also describe the subject of a sentence, which, in Japanese, comes before the ga が particle, which functions as subject marker. For example:

neko ga kawaii 猫が可愛い
Cats are cute.
inu ga kawaikunai 犬が可愛くない
Dogs are not cute.
natsu ga atsukatta 夏が暑かった
The summer was hot.
fuyu ga samukunakatta 冬が寒くなかった
The winter was not cold.

Adjectives used this way are called predicative adjectives, since they're part of the predicate for a grammatical subject. In Japanese, the form is called shuushikei 終止形.

Using the Copula

In Japanese, the words desu です and da だ are copulative verbs, also called copula. The English copula would be "to be," "is," "are," etc. Different from English, in Japanese the copula is often optional and omitted in phrases. For example:

neko ga kawaii 猫が可愛い
Cats, cute.
Cats [are] cute. (implicit copula.)
neko ga kawaii desu 猫が可愛いです
Cats are cute. (explicit copula.)

There's no difference between the meaning of the phrases above. There's a difference in nuance, because desu is a polite copula, but that's all. Likewise, all of the phrases below mean "cats are cute."

neko ga kawaii desu 猫が可愛いです
neko ga kawaii no desu 猫が可愛いのです
neko ga kawaii-n-desu 猫が可愛いんです
neko ga kawaii no da 猫が可愛いのだ
neko ga kawaii-n-da 猫が可愛いんだ

Note that, although you can say neko ga kawaii desu, you can't say neko ga kawaii da, as that's grammatically wrong. You must say neko ga kawaii-n-da or neko ga kawaii no da.

-i-n-da ～いんだ

This common construction, -i-n-da ～いんだ can be divided into three parts: an i-adjective, the n ん particle, which's the contraction of the no の particle, and the da だ copula.

This construction is necessary because you can only put nouns before the copula da だ, and an i-adjective is an adjective, not a noun. To fix that, you use the no の particle, that turns something into a noun. This no の particle is often contracted into an n ん. Basically:

kawaii 可愛い
(Adjective.)
kawaii no 可愛いの
(Noun.)
kawaii no da 可愛いのだ
(Rigid form.)
kawaii-n-da 可愛いんだ
(Contraction.)

You might be asking yourself why's it wrong to say -i-da instead of -i-n-da or -i-no-da, but it's alright to say -i-desu instead of -i-n-desu or -i-no-desu.

The answer is simple: it was wrong to say -i-desu, for the same reason, too: desu requires a noun before it, just like da. But because too many people kept saying it wrong, the rule was changed, so it's now considered grammatically alright to say -i-desu. But the rule wasn't changed for da, so it's still grammatically wrong to say -i-da. ^{[日本語の文法について、「～んです」の「ん」の文法的な使い方、意味を教えてください。 - detail.chiebukuro.yahoo.co.jp, 2018-10-27]}

Anyway, adding the copula (and no) is normally optional, and since it's optional, that means deliberately doing it must mean something by comparison, and what it ends up meaning is that it emphasizes your statement:

neko ga kawaii 猫が可愛い
Cats are cute.
neko ga kawaii-n-da 猫が可愛いんだ
I'm saying: cats. ARE. Cute.

(for reference, the anime Shinya! Tensai Bakabon 深夜！天才バカボン has a protagonist that says -n-da んだ a lot.)

-katta desu かったです

When using shuushikei adjectives in past tense with copula, the copula must be in non-past tense. That is, when you have an adjective in past -katta, you use da or desu, not datta or deshita.

To understand it better:

Correct: past + non-past.
- tanoshiikatta-n-da 楽しかったんだ
- tanoshikatta desu 楽しかったです
Wrong: past + past.
- tanoshikatta-n-datta 楽しかったんだった
- tanoshikatta deshita 楽しかったでした
Wrong: non-past + past.
- tanoshii-n-datta 楽しいんだった
- tanoshii deshita 楽しいでした

The English copula would be is, are, was, were, so the way it works in Japanese is different from how it works in English. In English we would say it was (past) fun (present).

Mostly because there's no past tense of "fun." If there were, like funned, Japanese would be like: "it is funned," tanoshikatta desu, to say "it was fun."

Again, the rules above only apply for shuushikei, when the adjective is at the end of the phrase, right before the copula:

eiga ga tanoshikatta desu 映画が楽しかったです
The movie was fun.

It doesn't apply if the adjective comes before a noun, i.e. rentaikei:

tanoshii eiga deshita 楽しい映画でした
It was a fun movie.

Furthermore, sometimes people say a phrase like the above but omitting the noun, which I don't if it's right or wrong but I'm writing it here for reference:

tanoshii ~~eiga~~ deshita 楽しい映画でした
It was a fun ~~movie~~.
tanoshii deshita 楽しいでした
It was fun. (what was?)
(The movie.) It was fun.

Better not to risk and stick with tanoshikatta desu.

Adverbial Form

In its adverbial form, an i-adjective can modify whatever verb comes right after it, just like any other adverb.

For example:

hayaku hashiru 速く走る
To run quickly. To run fast.
- hayai 速い
  Fast. Quick.
kawaiku mieru 可愛く見える
To look cute (now, as opposed to before.)
chikyuu ga chiisaku mieru 地球が小さく見える
The Earth looks small. (from space, etc.)
- chiisai 小さい
  Small.
takaku tonda 高く飛んだ
Jumped high.
- takai 高い
  High. Tall.
  Expensive.
takaku ureru 高く売れる
To be able to sell expensively.
To be able to sell for much money.
To be able to sell for a lot.

Adjectives Modifying Adjectives

Some adverbialized adjectives can also modify other adjectives. For example:

sugoi 凄い
Incredible.
sugoku tanoshii! 凄く楽しい！
Incredibly fun!

-Ku Naru ～くなる

When an adverbialized adjective comes before the verb "to become," naru なる, it implies something will become that adjective in the future. For example:

kuraku naru 暗くなる
[It] will become dark.
- kurai 暗い
  Dark.
hanashi ga nagaku naru 話が長くなる
The talk will become long. (literally.)
I.e.: the story will take a while to tell. "It's a long story..." Etc.
- nagai 長い
  Long.

-Ku Natta ～くなった

When the naru なる verb is conjugated to the past, natta なった, and modified by an adverbialized adjective, -ku natta ～くなった, it means it became that adjective in the past. For example:

kao ga akaku natta 顔が赤くなった
Face became red. (literally.)
[You're blushing!]
- akai 赤い
  Red.
kodomo ga ookiku natta 子供が大きくなった
Children became big. (literally.)
[The children have grown up.]
- ookii 大きい
  Big.

Te-Form ～て

The te-form of i-adjectives, or te-kei テ形 , is the ren'youkei 連用形 form, the one ending in -ku ～く, plus, literally, a -te ～て.

kawaii 可愛い
Shuushikei or rentaikei.
kawaiku 可愛く
Ren'youkei.
kawaikute 可愛くて
Te-kei.

In other words, the te-form of i-adjectives is the form that ends in ~kute ～くて.

This te-form is used to connect one adjective to another, which essentially means one thing is two or more adjectives at once.

One situation you see this in manga where this te-form is hard to miss is when a character starts listing all the good attributes of a girl or guy they like or hate. It goes on and on forever. For example:

yasashikute utsukushikute kawaikute kakkoyokute ii hito da. 優しくて美しくて可愛くてカッコよくていい人だ
[She's a] kind, beautiful, cute, cool, good person.

Like in English, stringing so many adjectives like that sounds weird. So most of the time you'll only ever see one -kute ～くて, two adjectives, no more no less.

yasashikute utsukushii hito da 優しくて美しい人だ
A kind, beautiful person.

Sometimes, the te-form can imply the first adjective causes the second. In this case the order of the adjective matters. For example:

Something ga X kute Y 〇〇がXくてY
Something is X and Y.
And it's Y because it's so X.
umi ga aokute utsukushii 海が青くて美しい
The sea is blue and beautiful.
And it's beautiful because it's so blue.
That is, blue is a beautiful color, so, by being blue, the sea is beautiful.

In most cases there's really only one order for the adjectives connected by the te-form. That's because the opposite order wouldn't make sense.

For example, above I might've implied the sea is beautiful because it's blue. If I said the opposite, umi ga utsukushite aoi, it would imply that the sea is blue because it's so beautiful, which makes less sense than saying it's beautiful because it's so blue.

A more interesting example of te-form ordering would be this:

takai 高い
Expensive.
hayai 速い
Fast.
takakute hayai 高くて速い
Expensive and fast.
It's fast because it's so expensive.
(e.g. you see an expensive car. Because it's expensive, you assume it's fast.)
hayakute takai 速くて高い
Fast and expensive.
It's expensive because it's so fast.
(e.g. you see a fast car. Because it's fast, you assume it's expensive.)

The te-form doesn't just connect i-adjectives to other i-adjectives. They can also be connected to nouns and to other types of adjectives. In particular, the te-form of na and no adjectives is de で. Example:

yasashikute kirei 優しくて綺麗
Kind and pretty.
kirei de yasashii 綺麗で優しい
Pretty and kind.

Note that in the example above there's no causal relationship between the two adjectives. Is she pretty because she's kind or kind because she's pretty? Neither seems likely so there's no implication an adjective is the cause of the other and it just means "kind and pretty" or "pretty and kind."

Te-Form and Color Adjectives

The te-form is normally not used to connect two colors together.

That's because if you have a red country flag, akai kokki 赤い国旗, then it's red. It can't be both red and blue and the same. I mean, if you can't say it in the shuushikei form, you can't say it in the rentaikei form. See:

akai kokki ga aoi 赤い国旗が青い
The red country flag is blue. (what? That doesn't make sense!)
akakute aoi kokki 赤くて青い国旗)
(therefore neither does this.)

Instead, to say something is of two colors in Japanese you'd say a noun phrase consisting of the colors connected by the to と particle, turned into an adjective through the no の particle. For example:

kokki ga aka to ao 国旗が赤と青
The country flag is red and blue.
aka to ao no kokki 赤と青の国旗
The red and blue country flag.

The same principle that allows the above allows colors to connect to non-color adjectives. Since they make sense in shuushikei, they make sense in rentaikei. See:

aoi umi ga utsukushii 青い海が美しい
The blue sea is beautiful.
aokute utsukushii umi 青くて美しい海
The blue, beautiful sea.

多い vs. 多くの

One gotcha concerning the Japanese language is the use of adjectives such as ooi 多い, "numerous," which vaguely describes the number of something.

In shuushikei, it works as you'd expect:

hito ga ooi 人が多い
People are numerous. People are many.
[There are lots of people here.]

However, in rentaikei you can't say it like this:

ooi hito 多い人
(wrong.)

My guess is this is because of how plurals work in Japanese: a single noun can be either singular or plural, and since it can be either singular or plural, hito 人 can mean either "(one) person" or "(multiple) people."

Obviously, with ooi hito, what we want to say is: "numerous people," "lots of people," but what it sounds like is that we're saying "one numerous person," "one lots-of person," and that makes no sense.

So, in Japanese, instead of saying ooi hito 多い人, we say:

ooku no hito 多くの人
Lots of people. Many people.

This word, ooku 多く, comes from the adverbial form of ooi, but is listed in Japanese dictionaries as a noun. ^{[おおく〔おほく〕【多く】 - dictionary.goo.ne.jp, 2018-10-25]}

So ooku no hito 多くの人, "numerous people," is syntactically identical to nihon no hito 日本の人, "Japan people," i.e. "people of Japan." It's a noun followed by a no の particle that turns it into a no adjective. Even though it was originally an i-adjective.

That's Japanese for ya, it makes no sense.

A more manga-ish example:

ooku no hito ga shinda 多くの人が死んだ
Lots of people died. Many people died.

Note that this is only the case in rentaikei, when the adjective comes before a noun, not in shuushikei, when the adjective comes at the end of a sentence or clause.

Which means you can have ooi hito if ooi is at the end of a subordinate adjectival clause. Which is basically whatever comes before a noun that describes that noun.

For example:

tomodachi ga ooi hito 友達が多い人
A person whose friends are numerous.
A person [that has many friends].
- The ooi above is at the end of the following subordinate clause:
- tomodachi ga ooi 友達が多い
  Friends are numerous. Friends are many.

-Sa ～さ

Adding the sa さ particle to the stem of an i-adjective translates into the -ness suffix in English. See:

amai 甘い
Sweet.
amasa 甘さ
Sweetness.

This form often implies the adjective is intense. That is, seldom we're talking about how little sweetness something has, so, usually, we're talking about how very sweet something is.

natsu ga atsui 夏が暑い
The summer is hot.
natsu no atsusa ni yowai 夏の暑さに弱い
Weak to the hot-ness of the summer.
Weak to the heat of the summer.
Weak to how hot the summer is.

As you can see above, sometimes the translation becomes quirky, but the concept remains the same.

ano tatemono ga takai あの建物が高い
That building is high.
ano tatemono no takasa あの建物の高さ
The high-ness of that building. (literally.)
The height of that building.
How high that building is.
anime ga tanoshii アニメが楽しい
Anime is fun.
anime no tanoshisa アニメの楽しさ
The fun-ness of anime.
How funny anime is.

-Sugiru ～すぎる

Adding the verb sugiru すぎる, "to exceed," to the stem of an i-adjective translates into "too X," or "exceedingly X," where X is the adjective. For example:

kawaisugiru 可愛すぎる
Too cute.
tanoshisugiru 楽しすぎる
Too fun.
atsusugiru 暑すぎる
Too hot.

-Sou ～そう

Adding -sou ～そう to the stem of an i-adjective translates into "seeming X," where X is the adjective. For example:

tanoshisou 楽しそう
It looks fun. It seems fun.
ureshisou 嬉しそう
He looks happy.
itasou 痛そう
It looks painful.

-Kereba ～ければ

The ba-form of i-adjectives, ba-kei バ形, is the kateikei 仮定形 form -kere ～けれ plus the ba ば particle, so, -kereba ～ければ.

This form is sometimes called the "conditional form," because it forms conditions. Basically "if X, then..." where X is the adjective.

yasui 安い
Cheap.
yasukereba, kaimasu 安ければ、買います
If cheap, buy. (literally.)
If [it's] cheap, [I'll] buy [it.]

kawaikereba nandemo yurusareru 可愛ければなんでも許される
If [you're] cute, anything can be forgiven.
Anything is allowed if you're cute.

yoi 良い
Good.
yokereba tsukatte kudasai 良ければ使ってください
If good, please use. (literally.)
If [it's] alright [with you,] please use [it].

-Kattara ～かったら

The tara-form of i-adjectives is the ren'youkei 連用形 form -ka' ～かっ plus the tara たら particle, so, -kattara ～かったら.

This tara たら particle is the kateikei 仮定形, "hypothetical form," of the auxiliary verb ta た, which makes the adjective's past form (-katta). ^{[たら - dictionary.goo.ne.jp, 2018-10-26]}

So, technically, it'd be the hypothetical past form. In practice, it's similar to -kereba, meaning "if X, then," where X is the adjective.

samukattara kiru 寒かったら着る
If cold, wear. (literally.)
If [it gets] cold, [I'll] wear [it.] (e.g. a sweater, etc.)

The difference between -kereba and -kattara being that the -tara form tends to be used with conditions for situations that'd occur only once. ^{[日本語文法条件 - www.coelang.tufs.ac.jp/mt/ja/, 2018-10-26]}

For example:

hoshii mono 欲しいもの
Wanted thing. Desired thing.
Something you want.
hoshikereba ubae 欲しければ奪え
If you want something, steal it.
(every time. A pirate's motto.)
hoshikattara ubae 欲しかったら奪え
If you want this one thing specifically, steal it.

-Kattari かったり

The tari たり form of i-adjectives is the ren'youkei 連用形 form -ka' ～かっ plus the tari たり particle, so, -kattari ～かったり.

This -tari ～たり form is used to say things in a "it's X, it's Y, etc." way. That is, it's used to vaguely list multiple attributes of something, and so it normally occurs twice or more in a phrase. For example:

saikin, atsukattari samukattari suru 最近暑かったり寒かったりする
Lately, it gets hot, it gets cold. (the weather keeps changing!)

With verbs, the tari form would vaguely list the things something does. Verbs and adjectives can be mixed this way. For example:

naitari, warattari, ureshikattari, kanashikattari 泣いたり、笑ったり、嬉しかったり、悲しかったり
Cry, laugh, be happy, be sad. (e.g. things a living being does.)

-Karou ～かろう

The volitional form of i-adjectives is the mizenkei 未然形 form -karo ～かろ plus the u う particle, so, -karou ～かろう.

This u う originates in a mu む.particle, that implied "conjecture," "supposition," suiryou 推量. ^{[う - dictionary.goo.ne.jp, 2018-10-25]}

So the volitional form means "I guess it's X" or "I hope it's X" or, as a wish, "let it be X!!!" Where X is an adjective.

Note that this -karou form is rather uncommon and archaic, and appears more set phrases. Usually, people prefer to use darou だろう or deshou でしょう, the volitional forms of the copula, rather than the volitional form of the adjective itself.

In manga and anime, this form is often used by kings and other empire or kingdom warrior-esque characters. The most common instance of it is probably:

yoi 良い
Good.
yokarou 良かろう
I suppose that's good.
I permit it.
I'll allow this plan.
Etc.

〇〇ろうが〇〇ろうが

Another rather situation it's used are in phrases like something-rou ga something-rou ga. Which means "be one thing or another," and is usually used when the two things are antonyms and the speak means "it doesn't matter if it's this or that!"

For example:

atsukarou ga samukarou ga dou-demo-ii!! 暑かろうが寒かろうがどうでもいい！！
Whether it's hot or cold I don't care!
Be it hot or cold I don't care!
I don't care if it's hot or cold!

This form isn't limited to adjectives. It can be mixed with verbs too.

aru ある
To exist. (verb.)
nai ない
Nonexistent. (adjective.)
kane ga aru 金がある
Money exists. (literary.)
To have money.
kane ga nai 金がない
Money is nonexistent. (literally.)
To not have money.
kane ga arou ga nakarou ga kankei nai! 金があろうがなかろうが関係ない！
Having money or not having money doesn't matter!
It doesn't matter if you have money or not!

tanoshikarou ga tsumaranakarou ga 楽しかろうがつまらなかろうが
Whether it's fun or boring.
korosou ga ikasou ga 殺そうが生かそうが
Whether you kill him or let him live.

-kare ～かれ

The imperative form of i-adjectives, meireikei 命令形, would be -kare ～かれ.

Note that this form is uncommon and archaic. Like -karou, it's used in manga and anime by kings, anachronistic characters, and in period settings. In modern Japanese, you'd link the adjective to a verb instead to form an imperative rather than using the imperative form of the adjective itself.

The term "imperative" refers to giving orders. For example, okiru 起きる is a verb for "to wake up." Its imperative conjugation, okirou 起きろう, would be ordering someone to "wake up!!!!1"

For adjectives, the imperative form, -kare, comes from the irregular verb aru ある, "to exist." The imperative conjugation of aru is are あれ. By stringing the adverbial form of an adjective with this imperative, and then corrupting the pronunciation, you get -kare. ^{[形容詞に命令形はありますか - detail.chiebukuro.yahoo.co.jp, 2018-10-27]}

For example:

utsukushii 美しい
Beautiful.
utsukushiku naru 美しくなる
To become beautiful.
- utsukushiku 美しく
  Adverbial form: beautifully.
- naru なる
  To become.
utsukushiku nare 美しくなれ
Become beautiful! (order.)
- nare なれ
  Imperative conjugation of naru.
(...likewise...)
utsukushiku aru 美しくある
To exist beautifully.
utsukushiku are 美しくあれ
Exist beautifully! (order.)
utsukushikare 美しかれ
(same as above.)

By the way, inflections of adjectives that merge -ku and aru together are called kari-katsuyou カリ活用, "kari inflections." This kari comes from ku ari, from the ari あり, "existing," noun form of aru ある. ^{[カリ活用 - 大辞林第三版 - via kotobank.jp, 2018-10-27]}

〇〇かれ〇〇かれ

Although archaic, the -kare inflection can still be found in some set phrases following a something-kare something-kare 〇〇かれ〇〇かれ form. For example:

osokare hayakare 遅かれ早かれ
Be late or be soon. (literally.)
Sooner or later.

Auxiliary Adjectives

The "auxiliary adjectives," hojo keiyoushi 補助形容詞, are i-adjectives that can be attached to verbs or other adjectives. The most common of them is nai ない, which makes stuff negative. There's also tai たい, makes stuff desiderative, which means "want to" more or less.

Since auxiliary adjectives are i-adjectives, they can be inflected like i-adjectives, and since you can attach auxiliary adjectives to i-adjectives, you can attach auxiliary adjectives to other auxiliary adjectives. For example:

akai 赤い
Red. (adjective.)
akaku-nai 赤くない
Not red.
1. Adjective.
2. Negative auxiliary adjective nai.

hataraku 働く
To work. (verb.)
hataraka-nai 働かない
To not work.
1. Verb.
2. Negative auxiliary adjective nai.
hataraki-tai 働きたい
To want to work.
1. Verb.
2. Desiderative auxiliary adjective tai.
hataraki-taku-nai 働きたくない
To not want to work.
1. Verb.
2. Desiderative auxiliary adjective tai.
3. Negative auxiliary adjective nai.

Since auxiliary adjectives are i-adjectives also follow i-adjectives rules. In particular, the ones about copula.

Correct:
- hataraki-taku-nai-n-da 働きたくないんだ
  DO NOT WANT TO WORK.
- hataraki-taku-nakatta desu 働きたくなかったです
  Didn't want to work.
Wrong:
- hataraki-taku-nai da 働きたくないだ
  (can't say -i da without no or n particle.)
- hataraki-taku-nai deshita 働きたくないでした
  (adjective must be in past tense, not copula.)

Nakunakunai なくなくない

By the way, this is pretty useless information, but technically Japanese allows you to add a negative auxiliary adjective to a negative auxiliary adjective. That's right: double negative.

sugoi! 凄い！
Incredible!
sugokunai 凄くない
Not incredible.
sugokunakunai 凄くなくない
Not not incredible. (yes, incredible.)
sugokunakunakunai 凄くなくなくない
Not not not incredible. (not incredible.)
sugokunakunakunakunai 凄くなくなくなくない
Not not not not incredible. (yes incredible)
(alright, you get it.)

Obviously the above is completely pointless if you're trying to... well, say something meaningful. But it can sometimes show up sometimes as a joke.

ウ音便

When i-adjectives come before the verbs gozaimasu ございます and zonjimasu 存じます, they suffer a change in pronunciation called u-onbin ウ音便, where the ending of the adjectives changes to ~ou or ~uu. Observe:

arigatai
有り難い
Hard to get. Unlikely to get.
Something you're thankful for getting, because it's rare.
arigataku gozaimasu
有り難く御座います
(since gozaimasu is a verb, the adverbial form is used.)
arigatou gozaimasu
有り難う御座います
Thank you. (expression.)

Note above that arigatai ありがたい became arigatou ありがとう. Adjectives that end in ~ai or ~oi become ~ou, while those that end in ~ui and ~ii becomes ~uu.

tsuyoi
強い
Strong.
tsuyou gozaimasu
強うございます
(same meaning.)

samui
寒い
Cold.
samuu gozaimasu
寒うございます
(same meaning.)

Game: Gyakuten Saiban 2 逆転裁判２

Kimiko
キミコ
(character name.)
yoroshuu gozaamasu.
よろしゅうござあます。
(...same as...)
- yoroshii
  よろしい
  Very well.
  That's fine.
  It's alright.
  Okay.

See the article on u-onbin ウ音便 for details.