じゃない: The Casual Way to Say 'Is Not' in Japanese

What it means

じゃない is the negative of だ (plain "is") for nouns and な-adjectives. Where you'd say 学生だ ("is a student"), the negative is 学生じゃない ("is not a student"). It's casual speech you'll hear among friends and family. To be polite, you add です on the end; for written or formal Japanese, じゃない becomes ではない. Note that じゃない is just a relaxed, spoken contraction of ではない — they mean exactly the same thing.

How to form it

Just drop じゃない directly onto the plain noun or な-adjective (no だ in between):

The な-adjective drops its な before じゃない: 静かな部屋 → 静かじゃない.

Polite and formal versions

You have three "not" options, from most casual to most formal. They all mean the same thing — only the register changes:

The past: じゃなかった

To say something was not, change ない to なかった — exactly like an い-adjective:

〜じゃない？ — the tag question

Here's the twist that surprises learners. With a rising tone, じゃない can flip its meaning and become a tag question — "right?", "isn't it?", "don't you think?" Instead of denying something, you're seeking agreement, and it often lands on a positive note:

Tone and context tell the two uses apart: a flat or falling tone is the plain negative ("is not"), while a rising tone is the tag question ("right?").

Common mistakes

1. Leaving だ in front of じゃない. Say 学生じゃない, not 学生だじゃない. The じゃない already replaces だ.
2. Keeping な on the adjective. Drop it: 静かじゃない, not 静かなじゃない.
3. Using じゃない with い-adjectives. い-adjectives have their own negative (高い → 高くない). じゃない is only for nouns and な-adjectives.
4. Missing the rising-tone meaning. いいじゃない！ with a rising tone means "that's good, isn't it!" — agreement, not denial. Listen for the tone.

Quick recap

• じゃない = casual "is not" for nouns and な-adjectives: 学生じゃない.
• Polite: じゃないです or じゃありません; formal/written: ではない.
• Past: じゃなかった ("was not").
• Rising-tone 〜じゃない？ = a tag question, "right? / isn't it?"
• It's only for nouns and な-adjectives — い-adjectives use 〜くない.

Your turn

Take the full N5 じゃない drill →