为什么？
The standalone 'Why?' Reach for this when someone has just said something and you want them to explain — a one-word follow-up. It works exactly like English 'Why?' as a complete utterance: another speaker drops a fact, you reply 为什么？and the conversation pivots to the explanation. It's neutral in tone; intonation and context do the rest of the emotional work. Don't confuse it with 为什么 used inside a longer sentence — here it stands alone.
Structure
为什么？
wèishénme?
How to Think About It
为什么 literally is 'for what,' and as a standalone it's the bare hook that pulls the next sentence out of your conversation partner. Unlike English, Chinese doesn't need 'do you' or 'is that' filler — the two characters are already a complete grammatical question. Stress and follow-up framing (curious, surprised, skeptical) come from your voice and face, not extra words.
Examples
—我不去了。—为什么？
— Wǒ bù qù le. — Wèishénme?
"I'm not going anymore." "Why?"
—这家店关门了。—为什么？
— Zhè jiā diàn guānmén le. — Wèishénme?
"This shop has closed." "Why?"
—他不喜欢这个工作。—为什么？
— Tā bù xǐhuān zhège gōngzuò. — Wèishénme?
"He doesn't like this job." "Why?"
Common Mistake
Learners try to soften the question by adding 吗 ('为什么吗？'). 吗 only attaches to yes/no questions; 为什么 is already a question word, so 吗 makes it ungrammatical. The neutral softener is 呢, not 吗.
为什么吗？
为什么？ (or 为什么呢？)
Don't Confuse With
为什么 [CLAUSE]？
Embedded in a full question — '为什么这么贵？' Use the standalone form only as a reactive follow-up; use the embedded form when you're asking about something specific in the same breath.
怎么了？
'What happened?' / 'What's wrong?' — asks about a situation, not a reason. Use 怎么了 when something seems off; use 为什么 when you want the cause of a stated fact.
为何？
Same meaning, formal/literary register. Use 为什么 in speech and casual writing; 为何 appears in news headlines and essays, almost never in conversation.
Practice
Reply with one Chinese word asking the reason: —我不去了。— ___？
Show answer
为什么
Fill in the missing character: 为___么？
Show answer
什
Arrange to ask a softened 'Why?': 呢 / 为什么
Show answer
为什么呢？
Translate the short dialogue: "I don't want to." "Why?"
Show answer
—我不想。—为什么？
Write a two-line dialogue where the second line is just 为什么？
Show answer
—明天不上课。—为什么？
Hear It in Real Episodes
This pattern appears in 1 Fluentide episode: