wǒ bú shì lǎoshī.

I am not a teacher.

Breakdown of wǒ bú shì lǎoshī.

• 我wǒ: I
• 是shì: to be
• 老师lǎoshī: teacher
• 不bù: not

Questions & Answers about wǒ bú shì lǎoshī.

Why is 不 pronounced as bú here instead of bù?

不 is normally pronounced bù (4th tone). When it comes directly before another 4th‑tone syllable, it changes to the 2nd tone bú. Since 是 is 4th tone, we say bú shì. Examples: bú duì (不对), bú yào (不要). In strong, contrastive emphasis some speakers keep bù, but the sandhi form bú before 4th tone is the default.

Do I need an article “a”? Can I say 我不是一个老师?

Chinese has no articles. 我不是老师 already means “I am not a teacher.” Adding a numeral-classifier often adds a nuance:

• 我不是一个老师 is uncommon in neutral statements; it can sound evaluative (“I’m not much of a teacher”) or contrast a specific counting context.
• If you must include one, prefer occupational/polite classifiers: 我不是一名老师 or 我不是一位老师—more formal and identity-focused than 一个.

Why do I need 是 here? Can’t I just say 我不老师?

When linking a noun/pronoun to a noun (identity/classification), Chinese uses the copula 是. So:

• Positive: 我是老师.
• Negative: 我不是老师. Without 是 (e.g., 我不老师) is ungrammatical in this equational pattern.

When do I use 不 versus 没/没有? Why not 我没是老师?

• Use 不 for general/habitual negation and to negate the copula: 不是.
• Use 没/没有 to negate existence, possession, or past/experiential events: e.g., 我没有老师 (“I don’t have a teacher”), 我没去 (“I didn’t go”).
• 我没是老师 is wrong. Say 我不是老师. To negate having been/working as a teacher, switch to a verb like 当: 我没当过老师 (“I’ve never been a teacher”).

How do I ask and answer “Are you a teacher?”

• Neutral yes–no: 你是老师吗？
• A‑not‑A pattern (often expecting confirmation): 你是不是老师？ Answers:
• Affirmative: 是(的)。/ 我是(老师)。
• Negative: 不是(的)。/ 我不是(老师)。 Adding 的 often sounds a bit more emphatic/insistent in answers.

Do I use 是 with adjectives? For example, “I’m not tall.”

No. Adjectives function like stative verbs; don’t use 是:

• “I’m not tall.” → 我不高 (wǒ bù gāo).
• But with nouns you do use 是: “He is not Chinese (a Chinese person).” → 他不是中国人. Here 中国人 is a noun phrase.

How do I say “I’m not the teacher” specifically?

Add a specific determiner/classifier:

• 我不是那个老师 (“I’m not that teacher.”)
• 我不是这位老师 (polite classifier 位; “I’m not this teacher.”) Bare 老师 is typically indefinite (“a teacher”).

How do I say “I have never been a teacher” or “I’m not currently working as a teacher”?

• Never been: 我没当过老师 / 我从来没当过老师.
• Not currently: 我现在不是老师 or 我现在没在当老师.
• Past time-specific: 那时候我不是老师 (“At that time, I wasn’t a teacher.”)

Can I drop the subject 我?

Yes, when context makes it clear. As a short reply:

• Q: 你是老师吗？ A: 不是。 In a full standalone statement, keep 我: 我不是老师。

Which measure words go with 老师?

Common ones:

• 位 (polite): 一位老师 (yí wèi lǎoshī)
• 名 (formal for professions): 一名老师 (yì míng lǎoshī)
• 个 (colloquial): 一个老师 (yí gè lǎoshī) Tone tip for 一: before a 4th tone it’s yí (e.g., yí wèi, yí gè); before 1st/2nd/3rd it’s yì (e.g., yì míng).

Is 老师 also a way to address someone? What about 教师?

Yes. 老师 is both the occupation “teacher” and a respectful form of address: 王老师 (“Teacher Wang”). 教师 is a formal job title (e.g., on certificates, 教师节) and is not used as a direct form of address.

Can 不是 stand alone as “No, it isn’t/No, I’m not”?

Yes. As a reply:

• 不是。 (“No, it isn’t / No, I’m not.”)
• Slightly more emphatic/polite: 不是的。 You can follow it with clarification: 不是，我是学生。

Why are there spaces in the given sentence? Do Chinese sentences use spaces?

The spaces are for learner segmentation. Standard Chinese writing does not use spaces between characters/words. You’d write: 我不是老师。 The Chinese full stop is 。 (though a western period is common in typed text).