Learn Hardcore Chinese: zhè gè rén bú shì lǎoshī.

In Mandarin, demonstratives 这/那 normally must be followed by a measure word (classifier) before a noun: 这 + 个 + 人. 个 is the default measure word for many nouns, including 人.

这个人 = this person (standard).
这人 exists in casual speech and can sound colloquial or a bit blunt, like “this guy.” For learners, use 这个人 as the safe, standard form.

What’s the word order here? Where does the negation 不 go?

Chinese is Subject–Predicate.

Subject: 这个人
Predicate: 不是老师 (verb/copula 是 with negation 不 before it, and the noun 老师).
Negation 不 is placed directly before verbs/adjectives, so you get 不 + 是 → 不是.

Why is 不 pronounced bú here and not bù?

Tone sandhi: 不 (bù) changes to rising tone bú when it comes before a fourth-tone syllable. 是 (shì) is fourth tone, so 不是 is pronounced bú shì.

Keep bù when the next syllable is not fourth tone: e.g., bù gāo.
In short, emphatic answers, speakers may keep bù even before a fourth tone (e.g., answering with bù shì for emphasis).

Why use 不 and not 没 for negation?

Use 不 for general, habitual, or present/future negation and with the verb 是. The negative of 是 is always 不是.
没 is used for past/completed events and to negate 有 (to have):

他不是老师 = He is not a teacher.
他没来 = He didn’t come.
他没有老师 = He doesn’t have a teacher.

Can I drop 是 and say 这个人不老师?

No. 是 is needed when linking a subject to a noun (copula with nouns).

Correct: 他是老师。/ 他不是老师。
With adjectives, you typically don’t use 是: 他很高 (He is tall).

How do I turn this into a yes–no question?

Two common ways:

Add 吗: 这个人是老师吗？ (Is this person a teacher?)
Use the A-not-A pattern: 这个人是不是老师？
A negative expectation question would be: 这个人不是老师吗？ (Isn’t this person a teacher?)

How do I make it plural, like “These people aren’t teachers”?

Use 这些 (these) and keep the noun without a plural ending:

这些人不是老师。
Avoid 老师们 here; 们 is mainly for pronouns or when addressing a known group (e.g., 老师们好 = Hello, teachers).

Is saying 这个人 polite? Is there a more respectful way?

这个人 can sound a bit blunt. For politeness, use the respectful measure word 位 and a title:

这位先生/女士 (this gentleman/lady)
这位老师 (this teacher)
If you don’t know the person’s role, 这位 on its own is also common in context.

Can I say 这不是老师 without 人?

Yes. 这不是老师 = This is not a teacher. You’re pointing to “this” (object or person) without specifying “person.” 这个人不是老师 explicitly says “this person is not a teacher.”

Why no 一 as in 这一个人?

After 这/那, you normally go straight to the measure word: 这个人, 那本书.
这一个人 is possible but adds emphasis to “this one person (as opposed to others).” It’s more marked.

What’s the nuance difference between 不是老师 and 不是个老师?

不是老师 is the neutral, standard “is not a teacher.”
不是个老师 can imply evaluative nuance like “not much of a teacher / not really a teacher (in quality).” It’s often pejorative or contrastive.

How do I say “He is not the teacher” vs “He is not a teacher” since there are no articles?

Chinese leaves definiteness to context. 他不是老师 can mean either. To force “the teacher,” specify:

他不是那位老师。
他不是我们班的老师。
These make it definite.

Can I add 的 at the end, like 不是老师的?

Sentence-final 的 can nominalize or add emphasis in elliptical contexts:

他不是老师的。 often appears when contradicting or contrasting prior info (“He’s not a teacher, actually”).
In a neutral standalone statement, 他不是老师 is more straightforward.

Is there any difference in pronunciation for 这? I hear zhèi sometimes.

Yes. In colloquial speech (especially northern accents), 这 before a classifier is often pronounced zhèi: zhèi ge rén. Both zhè ge rén and zhèi ge rén are acceptable in speech; zhè is standard in writing and teaching materials.

How would I say “This person is no longer a teacher”?

Add the change-of-state particle 了 after the predicate:

这个人不是老师了。
This signals a new situation compared to before.

What are the traditional characters for this sentence?

這個人不是老師。 (Pronunciation and grammar are the same.)