Japanese adjectives come in two families, and every learner has to master both in the first weeks. The families are called い-adjectives and な-adjectives. They look similar in a dictionary, but they behave differently in almost every sentence.
How to tell them apart
- い-adjectives end in い in their dictionary form: 高い, 安い, 大きい, 新しい, おいしい.
- な-adjectives do not end in い (usually), or the words look like nouns: 静か, きれい, 元気, 便利, 有名.
Before a noun, the difference shows:
- 高い本 — an expensive book (い-adjective stays as it is)
- 静かな部屋 — a quiet room (な-adjective adds な)
Present and past
い-adjectives change their own ending
| Form | Example |
|---|---|
| Present | 高い (expensive) |
| Present negative | 高くない |
| Past | 高かった |
| Past negative | 高くなかった |
Polite forms add です: 高いです, 高くないです, 高かったです, 高くなかったです.
な-adjectives use だ/です like nouns
| Form | Example |
|---|---|
| Present | 静かだ / 静かです |
| Present negative | 静かじゃない / 静かではありません |
| Past | 静かだった / 静かでした |
| Past negative | 静かじゃなかった / 静かではありませんでした |
The adjective itself never changes; the part after it does.
Connecting to verbs (adverbs)
- い-adjective: drop い, add く. 速い → 速く走る (run fast).
- な-adjective: add に. 静か → 静かに話す (speak quietly).
The same logic applies to ～くなる and ～になる: 寒くなる (gets cold), 静かになる (gets quiet).
Connecting two adjectives or clauses
- い-adjective: drop い, add くて. 安くて、おいしい (cheap and tasty).
- な-adjective: add で. 静かで、きれい (quiet and clean).
This is the adjective version of the て-form; the verb version is covered in Japanese て-form conjugation rules.
The exception: いい
いい (good) is an い-adjective with an irregular stem: よくない, よかった, よくて. Never ✕ いくない or ✕ いかった. This is a favorite test item.
The traps: words that end in い but are な-adjectives
Some な-adjectives end in い, which makes them look like い-adjectives. The most common:
- きれい (pretty, clean): きれいな花, きれいじゃない
- 嫌い (dislike): 嫌いな食べ物, 嫌いじゃない
- ゆかい (愉快, pleasant) and ていねい (丁寧, polite) also take な, not い-adjective endings.
If you are unsure, check how the word is used with a noun: きれいな, not きれいい.
What to do with な-adjectives and nouns
な-adjectives are close relatives of nouns: both use だ/です, both connect with で, and both take の or な before a noun depending on type. This is why 学生の本 (noun + の) and 静かな部屋 (な-adjective + な) look similar but are not the same rule.
Practice routine
- Sort 20 adjectives from your vocabulary into two columns, い and な.
- Write the four basic forms for each (present, negative, past, past negative).
- Make one sentence for each with a noun after it.
- Add the surprises (いい, きれい, 嫌い) to a mistake log and review weekly.
For long-term retention, review adjective forms with a schedule, as described in spaced repetition for JLPT vocabulary and kanji.
What the JLPT tests
- Choose the correct form to complete a sentence: 昨日は天気が（ ）です。 (よかった / いかった / よくだった...).
- Choose the correct connection to a noun or verb.
- Spot the wrong form in a sentence.
Mistakes on い vs な and on いい are among the most common at N5, so a short daily drill pays off quickly. The JLPT N5 grammar checklist shows the full scope.
Next steps
For the overall roadmap, see the JLPT preparation guide. JLPT Ready's Learn section presents each grammar point with a plain-language explanation and links to the practice questions that test it, and Practice mode explains every answer. You can start free with N5, no card required.