Japanese has two adjective classes: い-adjectives and な-adjectives. Both describe people and things, but they modify nouns, form negatives, express past time, and connect to other words differently. English changes a separate verb in “is expensive” and “was expensive.” Japanese often changes the adjective itself.
The basic difference
Most い-adjectives end in a conjugating い: 高い, 安い, 新しい, 面白い, 忙しい. A な-adjective normally appears as a stem in a dictionary and takes な before a noun: 静か, 便利, 元気, 有名.
| Type | Word | Before a noun | At sentence end |
|---|---|---|---|
| い-adjective | 高い | 高い山 | 山は高いです |
| い-adjective | 面白い | 面白い本 | 本は面白いです |
| な-adjective | 静か | 静かな町 | 町は静かです |
| な-adjective | 便利 | 便利なアプリ | アプリは便利です |
The な belongs only between a な-adjective and a noun. 町は静かなです is incorrect. At the end, say 町は静かです.
Words ending in い that are not い-adjectives
きれい and 嫌い（きらい） end in the kana い, but they are な-adjectives. The final sound is part of the stem, not the conjugating い ending.
きれいな花／a beautiful flower
この花はきれいです。／This flower is beautiful.
嫌いな食べ物／food someone dislikes
Check a dictionary when unsure. Visual endings provide a clue, not a complete classification rule.
Conjugating an い-adjective
For the negative, replace final い with くない. For the past, replace it with かった. The past negative is くなかった. Add です after the completed form for politeness.
| Form | 高い | Meaning |
|---|---|---|
| Non-past affirmative | 高いです | is expensive |
| Non-past negative | 高くないです | is not expensive |
| Past affirmative | 高かったです | was expensive |
| Past negative | 高くなかったです | was not expensive |
Incorrect: 高いじゃありません, 高いでした.
Correct: 高くないです, 高かったです.
The important irregular adjective いい
いい “good” conjugates from the older form よい:
いいです → よくないです → よかったです → よくなかったです
昨日の映画はよかったです。
Yesterday’s film was good.
Forms such as いくない and いいかった are incorrect. Learn the four-form set together.
Conjugating a な-adjective
At sentence end, a な-adjective follows a noun-like pattern.
| Form | 静か | Meaning |
|---|---|---|
| Non-past affirmative | 静かです | is quiet |
| Non-past negative | 静かじゃありません | is not quiet |
| Past affirmative | 静かでした | was quiet |
| Past negative | 静かじゃありませんでした | was not quiet |
ではありません and ではありませんでした are more formal alternatives. The adjective stem remains 静か; the sentence ending changes.
Linking descriptions with くて and で
An い-adjective replaces final い with くて. A な-adjective adds で.
この店は安くて、おいしいです。
This restaurant is inexpensive and delicious.
この町は静かで、便利です。
This town is quiet and convenient.
田中さんは元気で、親切です。
Tanaka is energetic and kind.
いい becomes よくて. The last adjective normally carries the tense: ホテルは静かで、便利でした means the hotel was quiet and convenient.
Turn adjectives into adverbs
To modify a verb, an い-adjective changes final い to く. A な-adjective adds に.
| Adjective | Adverb form | Example |
|---|---|---|
| 早い | 早く | 早く起きます。／get up early |
| 大きい | 大きく | 名前を大きく書きます。／write the name large |
| 静か | 静かに | 静かに話します。／speak quietly |
| 上手 | 上手に | 上手に歌います。／sing skilfully |
静かで話します is not the ordinary way to say “speak quietly.” で connects descriptions; 静かに directly modifies 話します.
Degree words come before the adjective
この本はとても面白いです。／This book is very interesting.
駅はあまり遠くないです。／The station is not very far.
この部屋は少し静かです。／This room is a little quiet.
あまり normally appears with a negative: あまり高くない, あまり便利じゃありません. とても normally strengthens an affirmative quality.
Comparing two things
東京と大阪と、どちらが大きいですか。
Which is larger, Tokyo or Osaka?
このかばんとそのかばんと、どちらが便利ですか。
Which bag is more convenient, this one or that one?
このかばんのほうが軽いです。
This bag is lighter.
The response pattern Aのほうが＋adjective means A is more so. The adjective class does not change because of comparison: 軽い remains an い-adjective; 便利 remains a な-adjective.
Using より for a direct comparison
東京は大阪より大きいです。
Tokyo is larger than Osaka.
電車はバスより便利です。
Trains are more convenient than buses.
English places “than” before the comparison target. Japanese places より after it. AはBより adjective is a useful starting pattern.
A connected description
私の町は小さいですが、便利です。駅の近くはにぎやかで、夜も明るいです。駅から遠い公園は静かで、空気がきれいです。
My town is small but convenient. The area near the station is lively and bright at night. The park far from the station is quiet, and the air is clean.
The paragraph combines い-adjectives such as 小さい and 明るい with な-adjectives such as 便利, にぎやか, 静か, and きれい. Classifying first makes it easier to choose ですが, くて, or で.
Common mistakes
- Treating きれい as an い-adjective: きれい花 instead of きれいな花.
- Keeping な before です: 静かなです instead of 静かです.
- Using でした after an unchanged い-adjective: 寒いでした instead of 寒かったです.
- Forgetting the irregular forms of いい.
- Connecting 安い with で instead of 安くて.
- Using 静かな before a verb instead of 静かに.
- Assuming Japanese comparison needs a separate “more” word before every adjective.
Practice
- Change 高い to non-past negative, past affirmative, and past negative.
- Use 静か before a noun, then make its non-past negative and past affirmative.
- What is the past affirmative of いい?
- Connect: この店は安いです。おいしいです。
- Connect: このホテルは静かです。便利です。
- Translate: “Please read quietly.”
- What class is きれい? Say “a beautiful flower.”
- Compare trains and buses using より and 便利.
Answers: 1 高くないです／高かったです／高くなかったです. 2 静かな町／静かじゃありません／静かでした. 3 よかったです. 4 安くて、おいしいです. 5 静かで、便利です. 6 静かに読んでください. 7 A な-adjective; きれいな花. 8 電車はバスより便利です.
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