〜です — Copula (Polite Be)

Properties

Meaning

です (desu) is the polite copula in Japanese. It links a noun or な-adjective to the predicate of a sentence, functioning as "is / am / are" in English. It carries no tense or aspect of its own beyond the forms shown below, and it never attaches directly to い-adjectives to form their predicate — those use their own inflection.

Conjugation

ではありません is the more formal written variant; じゃありません is the common spoken form.

With な-adjectives

な-adjectives attach directly to です.

With い-adjectives

い-adjectives carry their own conjugation endings. です is appended after the full い-adjective form only as a politeness marker — it does not replace the adjective's own ending.

Examples

1. わたしは学生です。 Watashi wa gakusei desu. I am a student.

2. あの建物は図書館じゃありません。 Ano tatemono wa toshokan ja arimasen. That building is not a library.

3. きのうはいい天気でした。 Kinō wa ii tenki deshita. Yesterday the weather was fine.

4. この料理はおいしいです。 Kono ryōri wa oishii desu. This dish is delicious.

5. 田中さんは親切な人です。 Tanaka-san wa shinsetsu na hito desu. Tanaka-san is a kind person.

Plain (Informal) Form

The plain-form equivalent of です is だ (da).

Use だ in casual speech, diary writing, and subordinate clauses inside a longer sentence (e.g. before と思う, らしい, etc.).

Common Mistakes

• Dropping the い before です — writing 大きです instead of 大きいです is ungrammatical. The い ending of an い-adjective must be kept; です does not replace it.
• Using じゃありません with an い-adjective — the negative of 高い is 高くありません, not 高いじゃありません.
• Confusing だ and です in formal writing — in polite registers (e.g. business email) always use です/ます forms throughout; mixing in だ sounds abrupt or rude.