Japanese Adjectives: い-Adjectives and な-Adjectives

Overview

Japanese has two distinct classes of adjectives: い-adjectives (i-keiyoushi) and な-adjectives (na-keiyoushi). Understanding the difference between these two classes is fundamental because they conjugate differently, connect to nouns differently, and follow different rules for negation and past tense.

い-adjectives are native Japanese words that always end in い (i) in their dictionary form: 大きい (ookii, "big"), 小さい (chiisai, "small"), 高い (takai, "tall/expensive"), 面白い (omoshiroi, "interesting"). They conjugate by themselves -- you change the ending directly without needing a copula.

な-adjectives are often borrowed from Chinese or other languages and behave more like nouns. They require な (na) when placed before a noun: 静か (shizuka, "quiet") becomes 静かな町 (shizuka na machi, "a quiet town"). They use the copula (です/だ) for their predicative form and follow noun-like conjugation patterns.

At CEFR A1, you need to confidently identify which class an adjective belongs to and conjugate both types in present, negative, past, and past negative forms. This is one of the grammar points that comes up in every single Japanese conversation.

How It Works

い-Adjective Conjugation

Drop the final い and add the ending:

Form	Rule	Example (高い, takai)
Present affirmative	い + です	高いです (takai desu) -- is expensive
Present negative	~くない(です)	高くないです (takakunai desu) -- isn't expensive
Past affirmative	~かった(です)	高かったです (takakatta desu) -- was expensive
Past negative	~くなかった(です)	高くなかったです (takakunakatta desu) -- wasn't expensive
Before a noun	い + noun	高い本 (takai hon) -- expensive book

Common い-Adjectives

Japanese	Reading	Meaning
大きい	おおきい (ookii)	big
小さい	ちいさい (chiisai)	small
高い	たかい (takai)	tall, expensive
安い	やすい (yasui)	cheap
新しい	あたらしい (atarashii)	new
古い	ふるい (furui)	old (things)
面白い	おもしろい (omoshiroi)	interesting, funny
難しい	むずかしい (muzukashii)	difficult
暑い	あつい (atsui)	hot (weather)
寒い	さむい (samui)	cold (weather)
長い	ながい (nagai)	long
短い	みじかい (mijikai)	short
いい/良い	いい (ii) / よい (yoi)	good

Special case: いい ("good") conjugates from its alternate form よい: よくない (yokunai), よかった (yokatta), よくなかった (yokunakatta).

な-Adjective Conjugation

Use the copula (です/じゃない) for conjugation:

Form	Rule	Example (静か, shizuka)
Present affirmative	+ です	静かです (shizuka desu) -- is quiet
Present negative	+ じゃないです	静かじゃないです (shizuka ja nai desu) -- isn't quiet
Past affirmative	+ でした	静かでした (shizuka deshita) -- was quiet
Past negative	+ じゃなかったです	静かじゃなかったです -- wasn't quiet
Before a noun	+ な + noun	静かな町 (shizuka na machi) -- quiet town

Common な-Adjectives

Japanese	Reading	Meaning
静か	しずか (shizuka)	quiet
きれい	きれい (kirei)	beautiful, clean
有名	ゆうめい (yuumei)	famous
元気	げんき (genki)	healthy, energetic
好き	すき (suki)	liked, favorite
嫌い	きらい (kirai)	disliked
大変	たいへん (taihen)	tough, serious
簡単	かんたん (kantan)	easy, simple
便利	べんり (benri)	convenient
大丈夫	だいじょうぶ (daijoubu)	okay, all right

Watch out: きれい (kirei) and 有名 (yuumei) end in い but are な-adjectives, not い-adjectives. The い is part of the word stem, not the adjective ending.

Comparison Table

Feature	い-Adjective	な-Adjective
Before noun	高い本 (no change)	静かな町 (add な)
Negative	高くない	静かじゃない
Past	高かった	静かだった
Adverb form	高く (add く)	静かに (add に)
Conjugates alone?	Yes	No (uses copula)

Examples in Context

Japanese	English	Note
この本は面白いです。	This book is interesting. (omoshiroi desu)	い-adj present
今日は暑くないです。	Today is not hot. (atsukunai desu)	い-adj negative
映画は長かったです。	The movie was long. (nagakatta desu)	い-adj past
大きい犬	a big dog (ookii inu)	い-adj before noun
この町は静かです。	This town is quiet. (shizuka desu)	な-adj present
彼女はきれいな人です。	She is a beautiful person. (kirei na hito)	な-adj before noun
元気じゃないです。	I'm not well. (genki ja nai desu)	な-adj negative
有名な映画	a famous movie (yuumei na eiga)	な-adj before noun
昨日はよかったです。	Yesterday was good. (yokatta desu)	Irregular いい → よかった
テストは簡単でした。	The test was easy. (kantan deshita)	な-adj past
古くて大きい家	an old, big house (furukute ookii ie)	Connecting い-adjectives
静かできれいな部屋	a quiet, beautiful room (shizuka de kirei na)	Connecting な-adjectives

Common Mistakes

Using だ/です after い-adjectives (in plain form)

• Wrong: 大きいだ。
• Right: 大きい。(plain) or 大きいです。(polite)
• Why: い-adjectives are already complete predicates on their own. Adding だ is grammatically wrong. です after い-adjectives is merely a politeness marker, not a copula.

Treating きれい and 有名 as い-adjectives

• Wrong: きれくない, 有名くない
• Right: きれいじゃない, 有名じゃない
• Why: Despite ending in い, these are な-adjectives. The い is part of the stem. Check: does it use な before a noun? If so, it is a な-adjective.

Forgetting the irregular conjugation of いい

• Wrong: いくない, いかった
• Right: よくない (yokunai), よかった (yokatta)
• Why: いい (good) switches to its alternate stem よ- for all conjugated forms. Only the dictionary/present form uses いい.

Using な before a noun with い-adjectives

• Wrong: 大きいな犬
• Right: 大きい犬
• Why: い-adjectives connect directly to nouns without な. Only な-adjectives need な.

Conjugating な-adjectives like い-adjectives

• Wrong: 静かくない
• Right: 静かじゃない
• Why: な-adjectives follow the copula pattern (じゃない, でした, etc.), not the い-adjective pattern (くない, かった).

Usage Notes

Both adjective types can be combined in a sentence using connecting forms:

• い-adjectives: drop い, add くて → 安くておいしい (yasukute oishii, "cheap and delicious")
• な-adjectives: add で → きれいで静か (kirei de shizuka, "beautiful and quiet")

In casual speech, です is often dropped entirely. Among friends: 面白い！ (omoshiroi! "That's interesting!"), 静か。 (shizuka. "It's quiet.").

Practice Tips

• Sort every new adjective immediately. When you learn a new adjective, determine if it is い or な. Write it in the appropriate column of your notebook. This prevents conjugation confusion.

• Practice all four forms together. For each adjective, drill: present → negative → past → past negative. 面白いです → 面白くないです → 面白かったです → 面白くなかったです. Do this until it is automatic.

• Describe photos or scenes. Look at a picture and describe everything: 大きい木があります。きれいな花があります。古い建物があります。This builds both adjective types in context.

Related Concepts

• Prerequisite: Copula です/だ -- な-adjectives use the copula for conjugation
• Next steps: Adjectives as Adverbs -- converting adjectives to modify verbs
• Next steps: Degree Adverbs -- words like とても and 少し that modify adjectives
• Next steps: Basic Comparison より -- comparing things using adjectives
• Next steps: Likes and Dislikes 好き/嫌い -- な-adjectives for expressing preferences
• Next steps: Appearance そう -- describing how things look