い and な adjectives

The one idea everything else comes from

さむい, by itself, is a complete sentence: "It is cold." しずか, by itself, is just the word "quietness." It needs だ／です to become a sentence.

Everything below is a consequence of this one difference.

Which class is a word in?

い-adjective: the final い is written in hiragana, outside the kanji.

• 高い（たかい）→ 高 is read たか, the い is separate
• 寒い（さむい）, 面白い（おもしろい）, 楽しい（たのしい）

な-adjective: every word that fails that test — anything whose final い is not a separate hiragana character sitting outside the kanji. In practice that covers three shapes:

• ends in an い sound, but the い is inside a kanji reading — 有名（ゆうめい）, 丁寧（ていねい）
• ends in some other sound — 静か（しずか）, 簡単（かんたん）, 変（へん）
• a loanword, which is always な — ハンサム, ユニーク, シンプル

The test is about where the い is written, not how the word sounds. 高い ends in い and 綺麗 ends in an い sound, but only 高い has that い as its own hiragana character after the kanji.

The look-alikes

These end in an い sound but are な-adjectives:

嫌い is the one that breaks the rule. It really is written with an okurigana い, and it really is a な-adjective (嫌いな人 = a person I dislike). It comes from the verb 嫌う, which is why. It's the main exception you'll meet at this level.

A shortcut when you can't see the kanji

い-adjectives are essentially a closed group — native Japanese words, no new ones being made. So:

• Katakana loanword → な (ハンサム, ユニーク, シンプル)
• Two-kanji Chinese-origin compound → な (有名, 簡単, 完璧, 便利, 失礼)
• Plain native word with a hiragana tail → い (寒い, 高い, 面白い)

(Modern slang does coin い-adjectives occasionally — エモい, キモい — but that's the only source of new ones.)

The です trap

This is the single biggest source of confusion, and it's worth understanding rather than memorizing.

です is doing two different jobs depending on the class.

With an い-adjective, です is just a politeness tag

The adjective already carries the tense. です adds nothing but politeness, so it never changes.

さむ + かった  ← tense lives here
さむかった + です  ← politeness lives here

With a な-adjective, です is the actual verb

しずか has no tense of its own, so です has to carry it — and to carry tense, it has to change.

しずか + でした  ← tense lives here

Side by side

Once you see that these are two different です, the "opposite" behavior stops feeling arbitrary.

Full conjugation

い-adjective — drop the い, add the ending

な-adjective — the word never changes; だ／です does

Register note: じゃ is the spoken contraction of では. In writing or formal speech: しずかではない／しずかではありません. Likewise さむくないです can be さむくありません. All correct; じゃ〜です is just the most conversational.

One irregular: いい. It conjugates from its older form よい.

• いい → よくない → よかった → よくなかった
• Never ✕ いくない, ✕ いかった
• Same in compounds: かっこいい → かっこよかった, 気持ちいい → 気持ちよかった

The four jobs an adjective does

This table is the practical heart of the document. Every adjective form you need is one of these four positions.

1. Ending a sentence

• きょうはさむいです。= Today is cold.
• このへやはしずかです。= This room is quiet.

2. Describing a noun

• さむいひ = a cold day
• しずかなへや = a quiet room
• ✕ しずかへや — the な is not optional

This is the only place な appears. Never ✕ しずかなです.

Negatives work here too, because ない is itself an い-adjective:

• さむくないひ = a day that isn't cold
• しずかじゃないへや = a room that isn't quiet

3. Joining ("and")

You can't just line adjectives up — the first one has to take the linking form.

• やすくて、おいしいです。= It's cheap and tasty.
• しずかで、ゆうめいです。= It's quiet and famous.
• いい → よくて

Only the last adjective takes the tense:

• やすくて、おいしかったです。= It was cheap and tasty.

4. Describing a verb

• はやく はしる = run quickly
• しずかに はなす = speak quietly
• ほんとうに おいしい = really tasty

Patterns from your later classes

All of these are built from the four jobs above.

なる — "become"

Uses job 4 (the adverb form).

• さむくなる = to get cold
• ゆうめいになる = to become famous
• よくなる = to get better

And it conjugates as a normal verb: ゆうめいになりたい, ゆうめいになりたかった, ゆうめいになりたくない.

すぎる — "too much"

い-adjective: drop the い, then add すぎる. な-adjective: add it directly.

• あまい → あますぎる = too sweet （not ✕ あまいすぎる）
• かんたん → かんたんすぎる = too easy
• いい → よすぎる

The result is an ichidan verb, so it conjugates like one: あますぎない, あますぎた, あますぎなかった.

みたい — "like / resembling"

みたい is itself a な-adjective, so it follows な rules:

• レモンみたいなオレンジ = an orange that's like a lemon
• みずみたいなコーヒー = coffee like water
• たなかさんみたいなひとになりたい = I want to become a person like Tanaka

とおもう / という / とき / んです — use the plain form

Before these, both classes go into their casual form. The asymmetry to watch:

Before とき and んです, な-adjectives go back to な:

• さむいとき / しずかなとき = when it's cold / when it's quiet
• さむいんです / しずかなんです

ほうが — comparisons

• あかとオレンジ、どっちのほうがすきですか？
• オレンジのほうがすきです。
• フェラーリのほうがたかいです。

が, not を, with すき／きらい／ほしい

These feel like verbs in English but are adjectives in Japanese. You're saying "X is likeable to me," so X takes が.

• あおが すきです。= I like blue. （✕ あおをすきです）
• なにが ほしいですか？ = What do you want?

（ほしい is an い-adjective: ほしくない, ほしかった.）

そう — "looks / seems"

A judgement from appearance, before you have any evidence. い-adjectives drop the い; な-adjectives take it bare.

• おいしい → おいしそう = looks tasty
• かんたん → かんたんそう = looks easy
• The result is itself a な-adjective: おいしそうな ケーキ, おいしそうに たべる.

Watch the other そう. Attached to a stem it means "looks"; attached to the plain form it means "I hear." おいしそうです = it looks tasty. おいしいそうです = I hear it's tasty. Same syllable, different attachment point, different meaning.

One restriction worth knowing: そう is for what you can't yet confirm. For qualities you can simply see — きれい, わかい — Japanese usually states the adjective plainly instead. きれいそう is grammatical, but it sounds like you're hedging about something already obvious.

ければ／なら — the "if" form

い-adjectives swap い for ければ. な-adjectives take なら, exactly as nouns do.

• やすい → やすければ かいます = if it's cheap, I'll buy it
• しずかなら いいです = if it's quiet, that's fine
• いい → よければ　(never ✕いければ)
• Negative: さむくなければ、しずかじゃなければ — because ない is an い-adjective too.

たら works on adjectives as well and is often easier: さむかったら, しずかだったら. The four conditionals are compared on the conjugation page.

Traps checklist

Two more worth knowing:

• 同じおなじ is a な-adjective that takes no な before a noun: おなじひと (not ✕ おなじなひと). But な does come back before ので／んです: おなじなんです.
• 違うちがう is a verb, not an adjective, even though English translates it as "different." ちがいます, ちがった. Never ✕ ちがいです.

Vocabulary from your notes

い-adjectives

な-adjectives