In short

A rhetorical question (反问句 fǎnwènjù) asks in order to assert, not to get an answer - and it means the opposite polarity of what it literally says. Two workhorses: 难道…吗 (nándào…ma), “do you mean to say…?!”, which flips whatever you put in it, and 不是…吗 (bú shì…ma), “isn’t it…? / didn’t…?”, which points at an obvious fact and always lands on a strong yes. Read them with feeling - surprise, reproach, or “you already know this”.

The rule

A rhetorical question looks like a yes/no question (it still ends in 吗), but the speaker is making a statement and expects no real answer. The trap for learners: the meaning is the reverse of the surface. A positive-looking question asserts a negative; a negative-looking question asserts a positive.

Step 1 - 难道…吗: put 难道 at the head, 吗 at the end.

难道 (nándào) means “could it really be that…? / do you seriously mean…?”. It sits at the front of the clause (before or right after the subject) and flags the whole sentence as an incredulous challenge. Normal word order in between; 吗 closes it.

难道 + [clause] + 吗？

The polarity flips:

• Positive clause -> negative assertion: 难道我错了吗？ (Nándào wǒ cuò le ma?) - Am I supposedly wrong? = I’m not wrong.
• Negative clause -> positive assertion: 难道你不知道吗？ (Nándào nǐ bù zhīdào ma?) - Do you really not know? = You do (or certainly should) know.

So to assert that someone does know, you insert the negation: 难道你不知道吗. The 吗 can be dropped once 难道 is present, and formal/literary Chinese swaps in 难道…不成 (nándào…bùchéng), but keep the 吗 in speech.

Step 2 - 不是…吗: frame a known fact as “isn’t it…?”.

不是 (bú shì) is a negation, but wrapped inside a question it produces a double flip and therefore a positive assertion. Use it to remind someone of something obvious, or to gently push back.

Subject + 不是 + [predicate] + 吗？

• 你不是答应了吗？ (Nǐ bú shì dāying le ma?) - Didn’t you agree? = You did agree.
• 这不是很好吗？ (Zhè bú shì hěn hǎo ma?) - Isn’t this great? = This is great.

不是…吗 always asserts the positive - there is no polarity choice to make, unlike 难道. Note that this 不是 is a fixed rhetorical frame, not the ordinary negation of the verb 是: the predicate after it need not contain 是 at all (你不是去过吗 uses 去, not 是). Pronunciation: 不 is written bù but said bú before a 4th tone, so 不是 is bú shì.

Step 3 - agree with the meaning, not the surface. Because the sense is inverted, you respond to the implied statement. To a rhetorical 你不是学生吗？ (“but you ARE a student, right?”), agreeing is 是啊 / 对啊 (shì a / duì a), never 不是.

This lesson owns only these assert-by-asking questions. Genuine yes/no questions that really seek an answer live in Yes/no questions with 吗 and sentence-final particles; content, A-not-A and choice questions live in Question-word, A-not-A and alternative questions.

Forms & patterns

The two frames and their built-in force:

How the polarity flip plays out - the question on the left means the plain statement on the right:

Examples

Common mistakes

• 难道他是老师。 -> 难道他是老师吗？ (Nándào tā shì lǎoshī ma?) - 难道 opens a rhetorical question, so it cannot be punctuated as a flat statement; in speech it closes with 吗 (or literary 不成), and even where the 吗 is dropped the sentence stays a question.
• 你知道难道吗？ -> 难道你知道吗？ (Nándào nǐ zhīdào ma?) - 难道 is a fronting adverb: it stands at the head of the clause, before or just after the subject, never after the verb.
• 难道你知道吗？（meaning “surely you know!”）-> 难道你不知道吗？ (Nándào nǐ bù zhīdào ma?) - with 难道 a positive clause asserts a negative; to assert that someone does know, put the 不 in.
• 你不是学生吗？——不是。（when you ARE a student）-> ……——是啊。 (…… — Shì a.) - 不是…吗 already means “you ARE a student, right?”; to agree, say 是 / 对, not 不是.

Tips

• Golden rule: read the reverse. A rhetorical question means the opposite of its surface. 不是…吗 always lands on a strong “yes”; 难道 flips whatever polarity you feed it. When you meet one, mentally state the plain sentence it stands for.
• Pick by how sharp you want to sound. 难道 is confrontational - incredulity, a challenge, even a rebuke (“you don’t seriously mean…?”). 不是…吗 is softer - “as you know / didn’t we agree…?”, nudging someone toward a shared fact.
• The words alone aren’t enough - tone and context decide. 你不是学生吗？can be a genuine question or a rhetorical one; adding 难道, or stressing the sentence, makes the rhetorical reading explicit and safe.
• Both frames still end in 吗, so they look like the yes/no questions from lesson 11 - the difference is that here no answer is wanted. If a reply is expected, it’s a real question; if you’re making a point, it’s 反问.