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Japanese adjectives: い-adjectives & な-adjectives

Japanese describing words come in exactly two flavours, and which flavour a word is decides how it changes for "not" and for "was". い-adjectives conjugate themselves, right on the end. な-adjectives don't change at all — they lean on です and let the ending do the work. Learn the two patterns once and every adjective falls into place. Here's how each kind behaves, plus the handful of traps that trip everyone up.

Two kinds, told apart by how they end

Every Japanese adjective is either an い-adjective or a な-adjective. The names come from what they do in front of a noun, but the real difference is how they conjugate.

So the question "is this an い-adjective?" isn't really "does it end in い?" — it's "does the い change when I make it negative?" Most words ending in い are い-adjectives, but a few famous ones (きれい, 嫌い) only look the part — more on those below.

い-adjectives: the self-changing kind

An い-adjective carries its own conjugation. Drop the final い and bolt on a new ending — no helper word needed. The plain forms below already are complete casual sentences ("it's expensive", "it wasn't expensive").

高い (takai, "expensive") — the four plain forms

Meaning	Plain (casual)	How it's built
is expensive	高い	takai — the dictionary form
is not expensive	高くない	takakunai — drop い, add くない
was expensive	高かった	takakatta — drop い, add かった
was not expensive	高くなかった	takakunakatta — negative, then past

To make any of these polite, just add です on the end — the adjective itself stays exactly the same:

Common い-adjectives to drill the pattern on: 大きい (big), 小さい (small), 新しい (new), 古い (old), 楽しい (fun), 忙しい (busy), 暑い (hot), 安い (cheap). Every one of them goes …くない / …かった.

な-adjectives: the ones that lean on です

A な-adjective never changes its own shape. Instead, the です/だ that follows it carries the negative and the past — exactly like a noun does. If you already know 学生です → 学生じゃない → 学生でした, you already know how な-adjectives conjugate.

静か (shizuka, "quiet") — same word, the ending does the work

Meaning	Casual	Polite
is quiet	静かだ	静かです
is not quiet	静かじゃない	静かじゃありません
was quiet	静かだった	静かでした
was not quiet	静かじゃなかった	静かじゃありませんでした

The word 静か sits there untouched in every cell; only the tail moves. (じゃ is the casual squeeze of では, so 静かではありません is the same thing, a notch more formal.) Common な-adjectives: 便利 (convenient), 好き (liked), 有名 (famous), 元気 (well), 大切 (important), 親切 (kind), 簡単 (easy).

Putting an adjective before a noun

This is where the two kinds get their names. To stick an adjective straight in front of the noun it describes (the way English does — "a red car"), an い-adjective just attaches, while a な-adjective needs な in between:

Describing a noun directly

Type	Japanese	English
い	赤い車	a red car (akai kuruma)
い	新しい本	a new book (atarashii hon)
な	静かな部屋	a quiet room (shizukana heya)
な	有名な人	a famous person (yūmeina hito)

That extra な is the whole reason these are called "な-adjectives." A useful check when you meet a new word: if it needs な to hug a noun, it's a な-adjective; if it clips straight on, it's an い-adjective. (Either way the adjective comes before the noun — Japanese always puts descriptions in front, as on the word-order page.)

The traps everyone hits

いい — the one irregular い-adjective

いい ("good") is the single irregular adjective, because it's really the modern face of an older word, よい (yoi). Whenever it conjugates, it reverts to the よ stem — it is never いくない:

Meaning	Correct	Wrong
good	いい / よい	—
not good	よくない	いくない
was good	よかった	いかった

This is why よかった ("(it) was good / phew, glad that worked out") is so common but いかった never appears. Compounds inherit it too: かっこいい (cool) → かっこよかった.

きれい, 嫌い — な-adjectives in い-adjective clothing

A few な-adjectives happen to end in the い sound, and beginners conjugate them like い-adjectives by mistake. The famous offenders:

Joining two adjectives: the て-form

To say "cheap and tasty" you don't repeat です; you put the first adjective into its connecting (て) form and let the sentence flow on. The pattern mirrors the two kinds:

Type	Connector	Example
い	…くて	安くて、おいしい — cheap and tasty
な	…で	静かで、きれい — quiet and pretty

So 高い → 高くて, and 便利 → 便利で. (The lone irregular shows up again: いい → よくて.) Only the last adjective in the chain carries the tense and politeness — everything before it stays in て-form.

Putting it together

1. Sort the word first. い-adjective or な-adjective? That single fact decides everything else.
2. い-adjectives conjugate themselves — …くない, …かった, …くなかった — and add です only for politeness.
3. な-adjectives don't move — the だ/です after them carries the negative and past, exactly like a noun.
4. Before a noun, い clips straight on; な needs its な.
5. Remember the two traps: いい conjugates from よ, and きれい/嫌い are な-adjectives.

Common questions

What are the two types of Japanese adjective?

い-adjectives and な-adjectives. い-adjectives end in the kana い and change their own ending for negative and past (高い → 高くない → 高かった). な-adjectives don't change shape — the です/だ after them carries the tense, and they take な before a noun.

How do you make a Japanese adjective negative?

い-adjective: drop い, add くない — 高い → 高くない. な-adjective: add じゃない (casual) or じゃありません (polite) — 静か → 静かじゃない. The exception is いい "good", which becomes よくない, never いくない.

How do you say something was [adjective] in the past?

い-adjective: drop い, add かった — 高かった "was expensive." な-adjective: use the past of the ending — 静かだった (casual) / 静かでした (polite). For polite い-adjectives just add です: 高かったです.

Why are きれい and 嫌い な-adjectives if they end in い?

Because they conjugate like な-adjectives, not い-adjectives: きれいじゃない, きれいな花. The い in きれい (written 綺麗) isn't an adjective ending — it just happens to be there. They're a small set of memorised exceptions.

What does adding な do?

The な links a な-adjective directly to the noun it describes: 静かな部屋 "a quiet room," 有名な人 "a famous person." い-adjectives don't need it — they attach straight on, like 赤い車 "a red car."

Next steps: see how a sentence is built in word order & SOV, meet the markers on the particles page, learn how verbs conjugate, or ask things in question words.