State-of-Being
だ / じゃない / だった / じゃなかった
Declare what something is (or isn't, or was) using the casual copula だ and its forms.
The topic particle は
Written は (ha) but pronounced "wa" when used as a particle. It marks the topic of the sentence — the thing the rest of the sentence is about. A natural English translation is "as for X…"
Declaring with だ (present affirmative)
Attach だ to a noun to declare a state of being. 「ねこ だ」 = "(it) is a cat." Combined with a topic: 「わたし は がくせい だ」 = "As for me, (I) am a student."
Negative — じゃない
Replace だ with じゃない for the negative. 「わたし は がくせい じゃない」 = "I am not a student." じゃない is a casual contraction of ではない.
Past — だった
Replace だ with だった for the past tense. 「それ は ほん だった」 = "That was a book."
Past negative — じゃなかった
Replace だ with じゃなかった for the past negative. 「それ は ねこ じゃなかった」 = "That wasn't a cat."
Casual vs. polite
These forms (だ / じゃない / だった / じゃなかった) are casual. The polite equivalents (です / じゃありません / でした / じゃありませんでした) are introduced in a later lesson. Use casual forms with friends and family; polite forms with strangers, customers, or superiors.
Vocabulary in this lesson
About the state-of-being form (だ)
State-of-being is the first thing most people learn in Japanese: how to say that one thing is another. In casual speech you do this with the copula だ — attach it to a noun and 「ねこ だ」 means "it's a cat." This lesson covers all four casual forms — present だ, negative じゃない, past だった, and past-negative じゃなかった — along with the topic particle は that sets up what the sentence is about. These plain forms are the foundation for the polite です forms you meet later, and they are core JLPT N5 grammar.
Frequently asked questions
What does だ mean in Japanese?
だ is the casual copula — the word that links a noun to a statement of being. 「がくせい だ」 means "(someone) is a student." It is the plain-form equivalent of the polite です.
What is the difference between だ and です?
They mean the same thing — "is" — but differ in politeness. だ is casual, for friends and family; です is polite, for strangers, customers, or people above you. This lesson teaches the casual だ; です is introduced in a later lesson.
How do I make だ negative?
Replace だ with じゃない. 「わたし は がくせい じゃない」 means "I am not a student." じゃない is the casual contraction of ではない.
How do I put だ into the past tense?
Use だった for the affirmative past (「ほん だった」 = "it was a book") and じゃなかった for the past negative (「ねこ じゃなかった」 = "it wasn't a cat").
Do I always need だ at the end of a sentence?
In casual speech だ is often dropped, especially in questions — 「がくせい？」 works on its own. But だった, じゃない, and じゃなかった are kept. Start by using だ so the structure is clear, then relax it as you get a feel for casual speech.
Credit
These lessons follow the structure, sequence, and grammar-first approach of Tae Kim's Guide to Learning Japanese. We are grateful to Tae Kim for making his guide freely available; the explanations here are our own retelling, and the interactive drills are original to this site.