Learn Hardcore Chinese: tā bù zhīdào zhè gè wèntí de yuányīn. - He doesn’t know the cause of this problem.

不 (bù)
- Negates general, habitual, or current states.
- Often used with stative verbs like 知道 (to know), 喜欢 (to like), 想 (to want/think).
- Example:
  - 我不知道。— I don’t know.
  - 他不喜欢咖啡。— He doesn’t like coffee.
没 (méi)
- Negates past events, completed actions, or possession.
- Often used with 有 (yǒu) or verbs with a completed‑action feel.
- Examples:
  - 我没去。— I didn’t go.
  - 我没钱。— I don’t have money.

知道 (zhīdào) here expresses a state: “to be in a state of knowing / not knowing”, not “to fail to know in the past as a one‑time event.”
So:

他不知道 = “He doesn’t know” (a fact / state now).
Using 没知道 is normally incorrect or at least very unnatural in standard Mandarin.

Why is 不 placed before 知道?

In Mandarin, negation words usually come directly before the verb or adjective they negate.

Pattern:

Subject + 不 + Verb/Adjective + …

In this sentence:

Subject: 他 (he)
Negator: 不 (not)
Verb: 知道 (to know)

So 他不知道 = He not know → “He doesn’t know.”

You almost never put 不 after the verb in Mandarin; “他知道不” is incorrect in this usage (though you’ll see Verb + 不 + Verb in question patterns like 会不会 / 好不好, which is a different structure).

What does 个 (gè) do after 这 (zhè), and why is it needed?

个 (gè) is a measure word / classifier. In Mandarin, when you use a number or a demonstrative (like 这 this, 那 that) before a noun, you almost always need a classifier between them.

Structure:

这 + 个 + Noun = this + (classifier) + noun

Here:

这 (this)
个 (gè) — general classifier
问题 (problem/question)

So 这个问题 literally means: “this (classifier) problem”.

You usually cannot say 这问题 in standard written Mandarin. In casual speech some people may drop 个, but 这个问题 is the normal, safe form to learn.

Why both 这 and 个? Could we just say one of them?

Each has a different role:

这 (zhè) — “this”, a demonstrative.
个 (gè) — classifier, required by grammar in “this + noun” structures.

You essentially need:

Demonstrative + Classifier + Noun

So:

× 这问题 — colloquially possible in some speech, but not standard and not ideal for learners.
✓ 这个问题 — grammatically standard and natural.

You cannot replace 个 with 这, or vice versa; they are not interchangeable.

What is 的 (de) doing between 问题 and 原因?

Here, 的 (de) links one noun (问题) to another noun (原因) to show a “of / belonging to / related to” relationship.

Pattern:

Noun1 + 的 + Noun2
= Noun2 that belongs to / is related to Noun1

In this sentence:

问题的原因
= the reason of the problem / the cause of the problem

So:

这个问题的原因
= “the cause of this problem” / “the reason for this problem”

This is very similar to “X’s Y” in English:

这个问题的原因 ≈ “this problem’s cause”
but in English we more naturally say “the cause of this problem”.

What is the difference between 问题 (wèntí) and 原因 (yuányīn) here?

They refer to two different things:

问题 (wèntí)
- “Problem” or “question”
- The thing that is wrong, unclear, or being asked.
原因 (yuányīn)
- “Cause” or “reason”
- The underlying reason why the problem exists or why something happened.

So:

这个问题 — “this problem / this question”
这个问题的原因 — “the reason (for) this problem” / “the cause of this problem”

The sentence says he doesn’t know why this problem exists, not just that he doesn’t know the problem itself.

Could we just say 他不知道这个问题? What is the difference in meaning?

Yes, 他不知道这个问题 is grammatically correct, but the meaning changes:

他不知道这个问题的原因。
→ He doesn’t know the cause/reason of this problem.
(He knows there is a problem, but not why.)
他不知道这个问题。
→ He doesn’t know about / know of / know (how to answer) this question/problem.

In context:

In a test situation, 他不知道这个问题 would most likely mean
“He doesn’t know the answer to this question.”
In a real‑life issue, it could also mean
“He is not aware of this problem at all.”

So adding 的原因 makes it clear we’re talking about the cause, not about knowing the question itself.

What exactly does 知道 (zhīdào) mean, and how is it different from 认识 (rènshi)?

知道 (zhīdào) means “to know (a fact, information, answer)”.

他不知道这个问题的原因。
→ He doesn’t know the reason (a piece of information).

认识 (rènshi) means “to know (a person) / to be acquainted with”.

我认识他。
→ I know him / I’m acquainted with him.
我不认识她。
→ I don’t know her (we haven’t met).

So you say:

知道 + fact/information
- 我知道答案。— I know the answer.
- 我不知道这个问题的原因。— I don’t know the cause of this problem.
认识 + person / sometimes place
- 我认识这个人。— I know this person.
- 我不认识这个地方。— I’m not familiar with this place.

Can 问题 (wèntí) mean both “problem” and “question”? Which one is it here?

Yes, 问题 commonly means both:

Problem / issue
- 这个电脑有问题。
  → This computer has a problem.
Question (like on a test or something you ask)
- 老师问了一个问题。
  → The teacher asked a question.

In 这个问题的原因, the most natural reading is:

“the cause of this problem/issue”.

It could, in a certain context (like a test), also mean:

“the reason for this question being asked / the background of this question”,

but usually, native speakers will understand it as “problem/issue” unless a test/exam context makes “question” more likely.

What are the tones of the words in this sentence, and is there any special tone change?

Tones:

他 — tā (first tone)
不 — bù (fourth tone)
知 — zhī (first tone)
道 — dao (neutral tone; sometimes written as dao·)
这 — zhè (fourth tone)
个 — gè (fourth tone; often very light/neutral in fast speech)
问 — wèn (fourth tone)
题 — tí (second tone)
的 — de (neutral tone)
原 — yuán (second tone)
因 — yīn (first tone)

Tone sandhi to note:

不 (bù) normally changes to bú before another fourth‑tone syllable
(e.g. bú shì instead of bù shì).
Here, 知道 (zhīdào) is first + neutral, not fourth tone, so 不 stays bù:
- bù zhīdào.

So there is no special tone change required in this particular sentence.

What is the difference between 他 (tā), 她 (tā), and 它 (tā), and why is 他 used here?

All three are pronounced tā, but written with different characters and used for different referents:

他 — “he / him”; male human, or gender‑neutral “he” in many cases.
她 — “she / her”; specifically female human.
它 — “it”; objects, animals (when gender is not emphasized), abstract things.

In 他不知道这个问题的原因, 他 is used, so the sentence refers to a male person (or just a generic “he” if gender isn’t important or specified).