Adjectives That Conjugate!
Here's something English never prepared you for: in Japanese, adjectives conjugate like verbs. "Is expensive", "was expensive", "isn't expensive", "wasn't expensive" — all of that happens inside the adjective itself. Once you see the system, it's beautifully regular, and it instantly upgrades your speech from single words to rich descriptions of past trips, cold days, and delicious meals.
You already met the two families in the vocabulary section. Now we learn what each family can do.
1. The Two Families, Reviewed
| Family | How to spot it | Examples |
|---|---|---|
| い-adjectives | end in 〜い in their base form | 高い (takai), おいしい (oishii), 寒い (samui), 楽しい (tanoshii) |
| な-adjectives | need な before a noun; behave like nouns | きれい（な）(kirei), 静か（な）(shizuka), 有名（な）(yūmei), 好き（な）(suki) |
The eternal trap, one more time: きれい (kirei, pretty/clean) and 有名 (yūmei, famous) end in the sound "i" but are な-adjectives. When you learn a new adjective, learn its family — this chapter shows why it matters.
2. Describing a Noun: The Two Connection Rules
| Family | Rule | Examples |
|---|---|---|
| い-adjective | attach directly | 高い山 (takai yama) — a tall mountain おいしいラーメン — delicious ramen |
| な-adjective | attach with な | 静かな部屋 (shizuka na heya) — a quiet room 有名な人 — a famous person きれいな花 — a pretty flower |
That な is where the family gets its name — it's the "glue" な-adjectives need before any noun. Forgetting it (きれい花 ✗) is the classic slip; hearing the correct きれいな花 a few dozen times will fix it forever.
3. Conjugating い-Adjectives
The rule: drop the final い, add the ending. です comes along at the end for politeness but never changes:
| Non-past | Past | |
|---|---|---|
| Affirmative | 高いです (takai desu) — is expensive | 高かったです (takakatta desu) — was expensive |
| Negative | 高くないです (takakunai desu) — isn't expensive | 高くなかったです (takakunakatta desu) — wasn't expensive |
The mistake every learner makes once: saying 高いでした for "was expensive". The past tense lives inside the adjective — 高かったです — never in です itself. Say it out loud three times: takakatta desu, samukatta desu, oishikatta desu. (A slightly more formal negative also exists: 高くありません = 高くないです. Both are correct polite Japanese.)
旅行は楽しかったです。(Ryokō wa tanoshikatta desu.) — The trip was fun.
昨日は寒くなかったです。(Kinō wa samukunakatta desu.) — Yesterday wasn't cold.
このかばんは高くないです。安いです!(Kono kaban wa takakunai desu. Yasui desu!) — This bag isn't expensive. It's cheap!
The one irregular: いい (good)
いい has an older twin, よい — and all conjugation happens on the よ side:
| is good | was good | isn't good | wasn't good |
|---|---|---|---|
| いいです | よかったです (yokatta desu) | よくないです (yokunai desu) | よくなかったです (yokunakatta desu) |
Bonus: よかった! alone is a joyful everyday exclamation — "Thank goodness!" / "I'm so glad!"
4. Conjugating な-Adjectives (You Already Know How!)
Wonderful news: な-adjectives conjugate exactly like nouns — the A は B です table from the sentence-structure chapter applies unchanged:
| Non-past | Past | |
|---|---|---|
| Affirmative | 静かです (shizuka desu) — is quiet | 静かでした (shizuka deshita) — was quiet |
| Negative | 静かじゃありません (shizuka ja arimasen) — isn't quiet | 静かじゃありませんでした (shizuka ja arimasen deshita) — wasn't quiet |
この町は静かです。(Kono machi wa shizuka desu.) — This town is quiet.
祭りはにぎやかでした。(Matsuri wa nigiyaka deshita.) — The festival was lively.
私は歌が上手じゃありません。(Watashi wa uta ga jōzu ja arimasen.) — I'm not good at singing.
So the family distinction pays off twice: it decides the noun-glue (direct vs な) and the conjugation pattern (internal 〜かった vs noun-style でした). Compare the pasts side by side: 楽しかったです (i-adj) vs にぎやかでした (na-adj).
5. Turning Adjectives into Adverbs
Adjectives can also describe how an action happens — "walk quickly", "study quietly":
| Family | Rule | Example |
|---|---|---|
| い-adjective | い → く | 早い → 早く起きます (hayaku okimasu) — get up early |
| な-adjective | + に | 静か → 静かに話します (shizuka ni hanashimasu) — speak quietly |
This 〜く form also powers the essential pattern 〜くなります "to become ~": 寒くなります (it's getting cold), 日本語が上手になります (your Japanese is getting good — な-adjectives use に here). A little preview of the grammar engine ahead!
6. Intensity Dials: とても, あまり, ぜんぜん
| Adverb | Meaning | Goes with | Example |
|---|---|---|---|
| とても (totemo) | very | affirmative | とてもおいしいです。— Very tasty. |
| あまり (amari) | not very | negative only! | あまり高くないです。— Not very expensive. |
| ぜんぜん (zenzen) | not at all | negative only! | ぜんぜん難しくないです。— Not difficult at all. |
あまり and ぜんぜん are magnets for negative endings — saying あまり高いです is ungrammatical. Hear the pairs as fixed melodies: あまり〜ない, ぜんぜん〜ない.
7. Practice: Describe Your World
Cover the answers and transform:
| Task | Answer |
|---|---|
| "a famous restaurant" | 有名なレストラン (yūmei na resutoran) |
| "an interesting book" | おもしろい本 (omoshiroi hon) |
| おいしいです → past | おいしかったです (oishikatta desu) |
| きれいです → past | きれいでした (kirei deshita — な-adjective!) |
| いいです → past | よかったです (yokatta desu) |
| 忙しいです → negative | 忙しくないです (isogashikunai desu) |
| "The test wasn't difficult at all." | テストはぜんぜん難しくなかったです。 |
| "The festival was very lively." | お祭りはとてもにぎやかでした。 |
Summary & Key Takeaways
- Two families, two behaviors — い-adjectives conjugate internally; な-adjectives behave like nouns with です.
- Before a noun: い-adj attaches directly (高い山); な-adj needs な (静かな部屋).
- い-adjective faces: 〜いです / 〜くないです / 〜かったです / 〜くなかったです. Never 〜いでした!
- いい conjugates on its よ twin: よかった, よくない, よくなかった. And よかった! = "thank goodness!"
- な-adjective faces are the noun table: です / でした / じゃありません / じゃありませんでした.
- Adverbs: い→く (早く), な→に (静かに); 〜くなります = "to become".
- Intensity: とても + affirmative; あまり and ぜんぜん + negative only.
- One chapter left in Grammar Foundations: asking questions like a pro — 何, どこ, 誰 and the こそあど system!