The present (dictionary) form of an い-adjective is the form you find in a dictionary, and it is the base every other form is built from. It always ends in the kana い, and it does two jobs with no helper word attached: it sits directly in front of a noun, and it ends a sentence all by itself. That second job is the one that trips up English speakers, because ending a sentence with an adjective feels like it should need a "to be" — and it doesn't. Once you see why, the plain present becomes the easiest form in the language.
The dictionary form ends in い
Every い-adjective ends in the hiragana い. The part before the い is the stem (often written with a kanji plus some okurigana), and the final い is what makes it an い-adjective. Here are the ones you will meet first:
| Adjective | Reading | Meaning |
|---|---|---|
| 高い | takai | high, tall, expensive |
| 安い | yasui | cheap, inexpensive |
| 大きい | ōkii | big |
| 小さい | chiisai | small |
| 新しい | atarashii | new |
| 面白い | omoshiroi | interesting, funny |
| 暑い | atsui | hot (weather) |
| 寒い | samui | cold (weather) |
A quick orthography note that saves confusion later: the final い is okurigana — kana hanging off the kanji stem. In 高い the kanji 高 carries the meaning and the い is the grammatical ending; in 新しい the stem is written 新し and only the last い is the class-marking ending. When you conjugate, you change that final い and leave the kanji alone — which is exactly why you can read a form like 高かった even before you have been taught it.
Attributive use: straight before the noun
To describe a noun, put the い-adjective directly in front of it. Nothing goes between them — no な, no の, no copula. English does the same thing ("a big dog"), so this half feels natural.
大きい犬が好きです。
ōkii inu ga suki desu
I like big dogs.
新しい携帯を買いました。
atarashii keitai o kaimashita
I bought a new phone.
安い店を探している。
yasui mise o sagashite iru
I'm looking for a cheap shop.
This is where な-adjectives diverge sharply: 静か (quiet) needs な (静かな部屋), and a noun needs の (木の椅子, "a wooden chair"). い-adjectives need neither. If you find yourself reaching for a linker after an い-adjective, that is English or な-adjective habit leaking in.
Predicate use: the adjective is the whole predicate
To say "X is [adjective]," you put the い-adjective at the end of the sentence — and stop. There is no separate word for "is." The adjective already contains it.
この犬は大きい。
kono inu wa ōkii
This dog is big.
今日はちょっと寒い。
kyō wa chotto samui
It's a little cold today.
この店、すごく安い。
kono mise, sugoku yasui
This shop is really cheap.
This is the mental hurdle for English speakers. In English, "The dog is big" has three words and a visible verb, is. In Japanese, この犬は大きい has no verb-that-means-"is" at all — 大きい does the predicating single-handedly. Think of an い-adjective as a tiny stative verb: 大きい already means "is-big," 寒い already means "is-cold." Reaching for a copula to add underneath it is like trying to say "is is-big."
です here is politeness, not "to be"
"But I always see 大きいです — what is です doing?" Fair question, and the answer is precise: です after an い-adjective adds politeness only. It does not supply the missing "to be," because nothing is missing. 大きい and 大きいです mean exactly the same thing; the second is simply the polite register.
この犬は大きいです。
kono inu wa ōkii desu
This dog is big. (polite)
今日は本当に暑いですね。
kyō wa hontō ni atsui desu ne
It's really hot today, isn't it? (polite)
The proof that this です is only politeness: it never changes for tense. The past of 大きい is 大きかった (the adjective carries the past), and the polite past is 大きかったです — です stays frozen while the adjective inflects. If です were a real copula it would become でした; the fact that ×大きいでした is wrong is the clearest sign that です here is a bolt-on politeness marker, not the verb "to be." The full politeness picture lives on the polite forms page.
Why this matters for everything downstream
Because the plain present already predicates, it is the launch pad for all the other forms — and each of them works by changing that final い, never by adding a copula:
- Negative: 高い → 高くない (see negative forms)
- Past: 高い → 高かった
- Past negative: 高い → 高くなかった
Get the plain present clean — "the word ends in い, needs no linker before a noun, needs no copula as a predicate" — and the rest of the い-adjective system is just controlled edits to that final syllable.
Common Mistakes
1. Adding です thinking a copula is grammatically required. です is politeness; the sentence is complete without it.
❌ この犬は大きいだ。
kono inu wa ōkii da
Wrong — い-adjectives never take だ, and no copula is needed at all.
✅ この犬は大きい。
kono inu wa ōkii
This dog is big.
2. Inserting な before the noun. That is な-adjective grammar; い-adjectives attach directly.
❌ 高いな山に登りたい。
takai na yama ni noboritai
Wrong — no な after an い-adjective.
✅ 高い山に登りたい。
takai yama ni noboritai
I want to climb a high mountain.
3. Inserting の before the noun. の links nouns to nouns; an い-adjective is not a noun.
❌ 面白いの本を読んだ。
omoshiroi no hon o yonda
Wrong — の would make it read as a nominalized 'the interesting one's book.'
✅ 面白い本を読んだ。
omoshiroi hon o yonda
I read an interesting book.
4. Treating です as a copula that changes for tense. です after an い-adjective is invariant.
❌ 昨日は暑いでした。
kinō wa atsui deshita
Wrong — the adjective carries the past: 暑かったです.
✅ 昨日は暑かったです。
kinō wa atsukatta desu
It was hot yesterday. (polite)
Key Takeaways
- The present form of an い-adjective ends in the kana い and is the base for every other form.
- Attributive: put it straight before the noun — no な, no の, no copula (大きい犬).
- Predicate: it ends the sentence by itself — the adjective is the "to be" (この犬は大きい).
- です adds politeness, not meaning; it never inflects, which is why ×大きいでした and ×大きいだ are both wrong.
- Read an い-adjective as a stative verb ("is-big") and the temptation to add a copula disappears.
Now practice Japanese
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Start learning Japanese→Related Topics
- i-Adjectives: Negative (〜くない)N5 — To negate an い-adjective you drop the final い and add くない (高い→高くない); the polite versions are 〜くないです and 〜くありません — and crucially you never use じゃない, which belongs to nouns and な-adjectives.
- i-Adjectives with ですN5 — How to make い-adjectives polite by adding です, including the polite negative and polite past.
- Two Adjective ClassesN5 — Japanese has two structurally different kinds of adjective — い-adjectives that conjugate themselves like verbs, and な-adjectives that are really nouns borrowing the copula — and this single split explains every adjective form you will ever meet.