Copula です/だ in Japanese

Overview

The copula in Japanese -- です (desu) in polite speech and だ (da) in plain speech -- is one of the very first grammar points you will learn. It functions similarly to the English verb "to be" when linking a subject to a noun or a な-adjective. For example, "This is a book" becomes これは本です (kore wa hon desu).

Unlike English, where "is/am/are" changes with the subject, です and だ do not change form based on who or what the subject is. Whether you are talking about yourself, another person, or an object, the copula stays the same. This makes it straightforward to use, though you do need to choose between the polite form (です) and the plain form (だ) based on the social context.

At CEFR A1, you will use です constantly. It appears in self-introductions, descriptions, questions, and nearly every basic sentence. Mastering the copula and its conjugations (negative, past, and past negative) is essential groundwork for all Japanese grammar that follows.

How It Works

Basic Forms

Form	Polite	Plain
Present affirmative	です (desu)	だ (da)
Present negative	じゃありません (ja arimasen)	じゃない (ja nai)
Past affirmative	でした (deshita)	だった (datta)
Past negative	じゃありませんでした (ja arimasen deshita)	じゃなかった (ja nakatta)

Sentence Pattern

The basic pattern is:

[Topic] は [Noun/な-Adjective] です。

• 私は学生です。(watashi wa gakusei desu) -- I am a student.
• 今日は月曜日です。(kyou wa getsuyoubi desu) -- Today is Monday.

With Questions

Add か (ka) to make a question:

• 学生ですか？(gakusei desu ka?) -- Are you a student?
• 元気ですか？(genki desu ka?) -- How are you? (lit. "Are you well?")

Polite vs. Plain

Situation	Use
Speaking to strangers, superiors, in public	です (polite)
Speaking with close friends, family, in casual writing	だ (plain)
Writing diary entries, internal thoughts	だ (plain)
Business, customer service	です (polite)

Important Notes

• です does not conjugate with い-adjectives the same way. You say 大きいです (ookii desu), not 大きいだ.
• In casual speech, だ is often dropped entirely in statements, especially by women: きれい (kirei) instead of きれいだ (kirei da).
• です after い-adjectives is a politeness marker, not a true copula.

Examples in Context

Japanese	English	Note
これは本です。	This is a book. (kore wa hon desu)	Basic identification
私は学生だ。	I am a student. (watashi wa gakusei da)	Plain form
元気ですか？	How are you? (genki desu ka)	Polite question
今日は日曜日です。	Today is Sunday. (kyou wa nichiyoubi desu)	Stating a fact
あの人は先生です。	That person is a teacher. (ano hito wa sensei desu)	Describing someone
日本人じゃありません。	I'm not Japanese. (nihonjin ja arimasen)	Polite negative
昨日は休みでした。	Yesterday was a day off. (kinou wa yasumi deshita)	Past polite
それは本じゃなかった。	That wasn't a book. (sore wa hon ja nakatta)	Past negative plain
彼は医者ですか？	Is he a doctor? (kare wa isha desu ka)	Yes/no question
ここは静かです。	This place is quiet. (koko wa shizuka desu)	With な-adjective

Common Mistakes

Using だ after い-adjectives

• Wrong: 大きいだ。
• Right: 大きい。 or 大きいです。
• Why: い-adjectives already function as predicates on their own. Adding だ is grammatically incorrect. Use です only as a politeness marker.

Forgetting to switch formality levels

• Wrong: Using だ when speaking to your teacher
• Right: Use です when speaking to teachers, strangers, and in formal situations
• Why: Using plain form with someone you should be polite to can sound rude or overly familiar.

Confusing じゃない with じゃありません

• Wrong: Using じゃない in a formal presentation
• Right: Use じゃありません or ではありません in formal contexts
• Why: じゃない is the casual negative. In polite speech, use じゃありません. For very formal writing, use ではありません.

Adding です to every sentence

• Wrong: 行きますです。
• Right: 行きます。
• Why: Verbs in ます-form are already polite. You do not add です after them.

Practice Tips

• Practice all four forms together. When you learn a new noun, immediately practice it in all forms: 学生です → 学生じゃありません → 学生でした → 学生じゃありませんでした. This builds automatic conjugation skills.

• Have self-introduction conversations. Practice はじめまして、[name]です。[occupation/nationality]です。どうぞよろしくお願いします。 This real-world pattern uses the copula repeatedly and is one of the first things you will need in Japanese.

• Listen for です/だ switching in anime or dramas. Notice how characters switch between polite and plain forms depending on who they are talking to. This builds your sense of when each form is appropriate.

Related Concepts

• Next steps: い-Adjectives -- adjectives that work differently from the copula
• Next steps: な-Adjectives -- adjectives that use the copula directly
• Next steps: Sentence-Final Particles -- particles added after です/だ for nuance
• Next steps: Formal Written Style -- advanced formality beyond です/だ