Adjective Conjugation
Learn the basic conjugation rules for both I-adjectives and Na-adjectives.
Adjectives Overview
In English, adjectives never change form — you say 'big,' 'was big,' 'not big' and the adjective stays the same. In Japanese, adjectives conjugate like verbs to express tense and negation directly, without needing extra words.
There are two groups. I-adjectives end in い and conjugate by changing that ending: 高い (expensive) → 高くない (not expensive) → 高かった (was expensive). Na-adjectives behave like nouns — they attach だ or です and follow the same conjugation patterns as noun predicates: 静かだ (quiet) → 静かではない (not quiet) → 静かだった (was quiet).
One important exception: the adjective いい (good) conjugates from the stem よ- in all forms except the dictionary form, so it becomes よくない, よかった, not いくない or いかった.
Below are the conjugation patterns for negative, past, and te-forms.
I-adjectives always end in the hiragana い. They conjugate by changing or removing this final い.
| Conjugated Form | Example |
|---|---|
Dictionary Form The base form of the adjective | |
高いたかい | この本は高い。 This book is expensive. |
Modifier Form Used to modify a noun (pre-noun) | |
高いたかい | これは高い本だ。 This is an expensive book. |
Negative Form Drop final い and add くない | |
高くないたかくない | この本は高くない。 This book is not expensive. |
Past Form Drop final い and add かった | |
高かったたかかった | この本は高かった。 This book was expensive. |
Past Negative Form Drop final い and add くなかった | |
高くなかったたかくなかった | この本は高くなかった。 This book was not expensive. |
Conditional Form (ba) Drop final い and add ければ | |
高ければたかければ | この本が高ければ、買いません。 If the book is expensive, I won't buy it. |
Adverbial Form Drop final い and add く | |
高くたかく | ボールを高く投げた。 I threw the ball high. |
Te-form (Connective) Drop final い and add くて | |
高くてたかくて | この本は高くて買えない。 This book is expensive and I can't buy it. |
Negative Te-form Drop final い and add くなくて | |
高くなくてたかくなくて | この本は高くなくて安い。 This book is not expensive and is cheap. |
In plain or informal Japanese, there are two ways to form the negative for Na-adjectives and nouns. ではない is more formal and common in writing, while じゃない is the informal, spoken version. I-adjectives use くない as their standard negative.
Examples
- It's not quiet today.
今日は静かではない。/ 今日は静かじゃない。
- This test isn't easy.
このテストは簡単ではない。/ このテストは簡単じゃない。
The のだ (formal) or んだ (informal) form is used to provide an explanation, seek clarification, or emphasize a reason. For I-adjectives, it follows the dictionary form. For Na-adjectives, it follows the dictionary form but replaces だ with な (making it 〜なのだ or 〜なんだ).
Examples
- I'm busy every day.
毎日忙しいのだ。/ 毎日忙しいんだ。
- I like it here.
ここが好きなのだ。/ ここが好きなんだ。
Adjectives can be turned into nouns using two main suffixes.〜さ focuses on objective measurement or degree (e.g., literal depth or height).〜み describes a subjective quality, flavor, or emotional depth. Some words can take both depending on the desired nuance.
〜さ (Degree / Measurement)
〜み (Quality / Taste)
Examples
- I was surprised at the height (expensive-ness) of the building.
ビルの高さに驚いた。
- I feel the deep sadness.
深い悲しみを感じる。
- The quietness of this park is nice.
この公園の静かさがいい。
- Have some of the sweetness of this fruit.
この果物の甘みを味わって。