な-Adjective + だ【だ (Predicate)】

In Japanese, な-adjectives (also called adjectival nouns or な形容詞) require the copula だ to form a predicate – that is, to complete a sentence. Unlike い-adjectives, which can end a sentence on their own, な-adjectives cannot stand alone and need だ (plain) or です (polite) after them.

Basic predicate use

To state that something is a certain quality, place the な-adjective before だ or です.

だ is the **plain form** used in casual speech and writing, while です is the **polite form** used in formal contexts.

Negative form

To say something is not a certain quality, replace だ with じゃない (plain) or ではありません / じゃありません (polite).

Past form

To describe a past state, use だった (plain) or でした (polite).

Past negative form

Use じゃなかった (plain) or ではありませんでした (polite).

Important note: だ vs. な

When a な-adjective modifies a noun, だ changes to な: しずか静かなへや部屋 (a quiet room), げんき元気なひと人 (an energetic person). However, when it serves as the predicate (at the end of a sentence), だ or です is used instead.

Common な-adjectives

Some common な-adjectives include しずか静か (quiet), げんき元気 (energetic), すき好き (liked), きらい嫌い (disliked), きれい (pretty/clean), ゆうめい有名 (famous), たいへん大変 (tough), かんたん簡単 (easy), and しんせつ親切 (kind). きれい and きらい嫌い look like い-adjectives but are actually な-adjectives – a common source of mistakes for learners.