じゃない: The Casual Way to Say 'Is Not' in Japanese
Saying something "is not"
じゃない is the negative of だ (plain "is"), and it works 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"). This is casual speech — the kind you'll hear among friends and family. One boundary to fix early: じゃない only negates nouns and な-adjectives. い-adjectives have their own negative (高い → 高くない), so you never reach for じゃない there.
ヤッタンは猫じゃない。
ヤッタンは ねこじゃない。
Yattan isn't a cat.
Noun + じゃない = casual 'is not.'
今日は元気じゃない。
きょうは げんきじゃない。
I'm not feeling well today.
元気 is a な-adjective, so it also takes じゃない.
モチは学生じゃないです。
モチは がくせいじゃないです。
Mochi isn't a student.
Add です to make it polite.
Attaching it cleanly
じゃない slots directly onto the plain noun or な-adjective — with nothing in between:
| What you have | Pattern | Example |
|---|---|---|
| Noun | noun + じゃない | 先生じゃない (isn't a teacher) |
| な-adjective | adj + じゃない | 静かじゃない (isn't quiet) |
| Polite | + です | 先生じゃないです |
| More formal polite | じゃありません | 先生じゃありません |
| Formal / written | ではない | 先生ではない |
Two attachment slips account for most errors. First, don't leave だ in front: it's 学生じゃない, never 学生だじゃない, because じゃない already stands in for だ. Second, drop the な off the adjective — 静かな部屋 becomes 静かじゃない, not 静かなじゃない.
Dialing the politeness up or down
You have three "not" options, running from most casual to most formal. They all mean the same thing — じゃない is simply a relaxed, spoken contraction of ではない — so only the register changes:
| Form | Core idea | Example |
|---|---|---|
| じゃない | casual (friends, family) | 学生じゃない = isn't a student |
| じゃないです / じゃありません | polite | 学生じゃないです = isn't a student |
| ではない / ではありません | formal, written | 学生ではない = isn't a student |
ヤッタンの弟は先生じゃありません。
ヤッタンの おとうとは せんせいじゃありません。
Yattan's little brother isn't a teacher.
じゃありません is a touch more formal than じゃないです.
これは問題ではない。
これは もんだいではない。
This is not a problem.
ではない suits writing and formal speech.
Shifting it into the past
To say something was not, swap ない for なかった — the ない behaves exactly like an い-adjective:
| Tense | Casual | Polite |
|---|---|---|
| Is not | じゃない | じゃないです |
| Was not | じゃなかった | じゃなかったです |
昨日は暇じゃなかった。
きのうは ひまじゃなかった。
I wasn't free yesterday.
暇 is a な-adjective; じゃなかった = 'was not.'
先生は元気じゃなかったです。
せんせいは げんきじゃなかったです。
The teacher wasn't well.
Add です for the polite past.
When 〜じゃない？ means "right?"
Here's the twist that surprises learners. With a rising tone, じゃない flips its meaning and becomes a tag question — "right?", "isn't it?", "don't you think?" Instead of denying something, you're fishing for agreement, and it usually lands on a positive note. This is also the one place じゃない clips onto an い-adjective (おいしいじゃない！), since it's no longer negating — so listen for the tone before you read it as a denial:
このケーキ、おいしいじゃない！
このケーキ、おいしいじゃない！
This cake is delicious, isn't it!
Rising tone — not 'not delicious' but 'it's delicious, right?'
モチ、それでいいじゃない？
モチ、それで いいじゃない？
Mochi, that's fine, isn't it?
Asking for agreement, not negating.
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?").
Keep in your pocket
- 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.
Practice it
Choose the correct negative form with じゃない.
＿＿＿に入れるのに最もよいものを選びなさい。
Choose the grammar pattern that best completes the sentence.
ヤッタンは猫＿＿＿。
Frequently asked questions
What's the difference between じゃない and ではない?
They mean the same thing — 'is not.' じゃない is a casual spoken contraction; ではない is more formal and common in writing. じゃないです and ではありません are the polite middle ground.
Can I use じゃない with い-adjectives?
No. い-adjectives form their own negative by changing 〜い to 〜くない (高い → 高くない). じゃない is only for nouns and な-adjectives.
How do I say 'was not' with じゃない?
Change ない to なかった: 学生じゃなかった ('wasn't a student'), 元気じゃなかった ('wasn't well'). Add です for the polite past: じゃなかったです.
Why does おいしいじゃない sound positive?
With a rising tone, 〜じゃない becomes a tag question meaning 'right?' or 'isn't it?' So おいしいじゃない！ means 'It's delicious, isn't it!' — agreement, not negation. Tone is the key.
Where じゃない fits
Don't confuse it with
- は · N5 — は marks the topic of a sentence — 'as for X.' Learn how it flags known information, its contrast use, why it's read 'wa,' and how it differs from が.
Once this clicks, go on to
- が · N5 — が marks the grammatical subject and introduces new information. Learn how to use が with question words, existence (ある/いる), ability, and likes such as 好き — plus how が differs from は.
More N5 grammar to explore
Keep going with related patterns at the same level:
- か Particle — The particle か turns a statement into a question (〜ですか), means 'or' between nouns (AかB), and makes question words indefinite: だれか someone, なにか something, どこか somewhere.
- まで — まで marks an end point in time or space — 5時まで ('until 5'), 駅まで ('to the station'). Learn how it pairs with から for 'from…to,' and how まで differs from までに.
- 〜ます — 〜ます is the polite verb ending. Learn ます (non-past), ません (negative), ました (past), and ませんでした (past negative), how to build the stem, and when to be polite.
- 〜ながら — 〜ながら describes doing two actions at the same time ('while doing'). Learn the formation from the ます-stem, which action is the main one, and see clear examples.
- 〜になる / 〜くなる — なる means 'become.' Learn the three patterns: noun + に + なる, な-adjective + に + なる, and い-adjective (drop い) + く + なる, plus how なる differs from する.
- 〜にする — 〜にする means to decide on or choose something (コーヒーにします = I'll have coffee) and to deliberately make X a certain way (静かにする). Learn the pattern and how it differs from なる.