い-adjectives: 大きい, 高い, 新しい and how they change

Adjectives let you describe things: a big station, an expensive apartment, a difficult test. Japanese has two types of adjectives. This lesson covers the first type, い-adjectives, which end in い and change their ending like verbs do.

What is an い-adjective?

An い-adjective ends in い in its basic form: 大おおきい (big), 高たかい (expensive; tall), 新あたらしい (new), おいしい (tasty). Add です to be polite: このラーメンはおいしいです — “This ramen is tasty.”

The four forms

To change an い-adjective, drop the last い and add a new ending. です stays at the end to keep it polite.

Tense	Affirmative	Negative
Present	高たかいです — is expensive	高たかくないです — is not expensive
Past	高たかかったです — was expensive	高たかくなかったです — was not expensive

You may also hear 高たかくありません and 高たかくありませんでした for the negatives. They are a little more formal and mean the same.

The irregular いい

いい (good) is the only irregular い-adjective. Its other forms come from the older word よい: よくないです (not good), よかったです (was good), よくなかったです (was not good). Never say “いくない” or “いかった”.

い-adjective + noun

Put the adjective directly before the noun — no extra word: 大おおきいえき (a big station), 新あたらしいスマホ (a new smartphone), 安やすいレストラン (a cheap restaurant). To ask “what kind of …?”, use どんな: どんなへやですか — 新あたらしいへやです.

高たかい has two meanings: “expensive” for prices and “tall/high” for buildings and mountains. Its opposite depends on the meaning: 安やすい (cheap) or ひくい (low).

Common mistakes

• Making the past with でした: “おいしいでした” is wrong; say おいしかったです.
• Using the regular pattern for いい: say よくないです, not “いくないです”.
• Putting な between an い-adjective and a noun: 大おおきいかばん, not “大きいなかばん”.
• Mixing up 大おおきい/小ちいさい (size) and 高たかい/安やすい (price).

How to practise

• Describe five things in your room with an い-adjective + noun.
• Describe your hometown in the present, then your last trip in the past.
• Practise the four forms of いい until they come automatically.
• Do the worksheet: kanji writing, matching and the “make it negative/past” exercise.