Japanese study guide
い-Adjectives vs な-Adjectives: The Difference
Japanese has two adjective classes that conjugate differently. How to tell them apart, the full conjugation grid, and the exceptions that catch everyone.
English adjectives don't change. "Expensive" is expensive in every tense, positive or negative, and the verb carries the grammar. Japanese splits the job differently: い-adjectives conjugate like verbs, and な-adjectives behave like nouns. Getting the two classes mixed up is the single most common beginner error, and it's completely avoidable.
Telling them apart
い-adjectives end in い in dictionary form and that い is part of the word: 高い (expensive), 新しい (new), 楽しい (fun), いい (good).
な-adjectives need な to attach to a noun: 静かな部屋 (a quiet room), 有名な人 (a famous person), 便利な (convenient), 元気な (healthy).
The trap: a handful of な-adjectives also end in い. The ones you'll actually meet are きれい (pretty/clean), 嫌い (disliked), 有名 (famous), 丁寧 (polite/careful), and 幸い (fortunate). They take な and conjugate like nouns: きれいな人, not きれい人, and never きれくない.
For most of them the writing gives it away: the final い is inside the kanji reading rather than an inflecting tail: 有名 is ゆうめい as a unit, with nothing to conjugate, unlike 高い. 嫌い is the genuine exception (it comes from the verb 嫌う), so just memorize that one. There are only a few; they're a spelling coincidence, not a category.
Conjugating い-adjectives
Drop the い and add the ending. Note that です does not conjugate here; the adjective does.
| Form | Example (高い) | Meaning |
|---|---|---|
| Present | 高いです | is expensive |
| Negative | 高くないです | isn't expensive |
| Past | 高かったです | was expensive |
| Past negative | 高くなかったです | wasn't expensive |
| Linking (て) | 高くて | expensive and… |
| Adverbial | 高く | expensively |
Common error: 高いでした. The past goes on the adjective (高かった), not on です.
いい is irregular. 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.
Conjugating な-adjectives
These behave like nouns: です carries the grammar, exactly as it does after a noun.
| Form | Example (静か) | Meaning |
|---|---|---|
| Present | 静かです | is quiet |
| Negative | 静かじゃないです | isn't quiet |
| Past | 静かでした | was quiet |
| Past negative | 静かじゃなかったです | wasn't quiet |
| Linking (て) | 静かで | quiet and… |
| Adverbial | 静かに | quietly |
| Before a noun | 静かな部屋 | a quiet room |
Compare directly: 静かでした (な-adj, です carries the past) vs 高かったです (い-adj, the adjective carries it). That contrast is the whole lesson.
Linking two adjectives
- 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 pretty)
Same job as the te-form of verbs, and it's the natural way to stack descriptions instead of repeating です.
Making adverbs
- い-adjective: い → く → 早い → 早く (quickly)
- な-adjective: + に → 静か → 静かに (quietly)
The fastest way to internalize this
Don't drill the tables. Two conjugation grids are easy to read and hard to retrieve at conversation speed; what actually transfers is having heard the correct form dozens of times in context.
So the practical route is: understand the rule once (you just did), then get volume of exposure to real sentences using both classes. Every adjective you learn should arrive inside a sentence, in its conjugated form, with audio. That's what makes 高かったです feel wrong-if-changed rather than requiring a lookup.
Adjective conjugation is learned the way native patterns are learned: by repeated correct exposure, not by re-reading the table. Adjectives are heavily represented in the N5 and N4 sets; see essential N5 vocabulary and the full N5 grammar list.