い-adjectives and な-adjectives
Japanese adjectives split into two camps: ones that end in い (called 'い-adjectives') and ones that don't (called 'な-adjectives' because they take な before a noun). They behave differently in both predicate and attributive position. Today you'll meet a handful of each, and learn how to make them positive, negative, and polite.
い-adjectives — already half a verb
おおきい (big), ちいさい (small), たかい (tall / expensive), やすい (cheap), おもしろい (interesting), おいしい (tasty). They all end in い. To use one before a noun, just stick it on: おおきい いえ = a big house. To make a polite sentence, put the adjective before です: この ほん は おもしろい です。 = 'This book is interesting.' The い stays — です is just there for politeness.
な-adjectives — noun-like
しずか (quiet), きれい (pretty / clean — careful, looks like an い-adjective but isn't), ゆうめい (famous), げんき (energetic / well), ひま (free, not busy). To use one before a noun, add な: しずか な ところ = a quiet place, きれい な はな = pretty flowers. As a predicate, just add です: へや は しずか です。 = 'The room is quiet.' No な before です — only before nouns.
Negation: い-adjectives
Drop the final い and add -くない: おおきい → おおきくない (not big). おもしろい → おもしろくない. Politely: おおきくない です or the slightly more formal おおきく ありません. One irregular: いい (good) becomes よくない (not good), not いくない — because いい secretly comes from older よい.
Negation: な-adjectives
Same as a noun: add じゃ ありません (or では ありません). しずか → しずか じゃ ありません (not quiet). げんき → げんき じゃ ありません. Treat な-adjectives as 'noun-like' and the negation pattern from lesson 3 just applies.
Putting them in front of nouns
Side by side: おおきい いえ (い-adj, no extra particle) vs しずか な いえ (な-adj, needs な). The な is the whole point of the name. きれい is an exception worth flagging: although it ends in い, it behaves like a な-adjective: きれい な はな, not 'きれいい はな'.
