I-Adjectives vs Na-Adjectives

In Japanese, every adjective belongs to one of two families: i-adjectives or na-adjectives.

I-adjectives always end in the Hiragana 'い' (i). For example: 大きい (ookii - big), 高い (takai - high/expensive). They change their own endings to express past or negative.

Na-adjectives act more like nouns. They require 'な' (na) to connect to other nouns, and they rely on 'です' (desu) to change into past or negative forms. For example: 静か (shizuka - quiet), きれい (kirei - beautiful).

N5 loves to test the traps in this system: きれい and 有名 look like i-adjectives because they end in い, but they conjugate as na-adjectives (きれいな人, not きれい人). いい (good) is the opposite trap: it looks like a normal i-adjective but its past and negative forms are irregular (よかった, よくない), built from the old form よい rather than いい itself.