Chinese phrases

How to say why in Chinese

Why in Chinese is 为什么 (wèi shén me). When you are surprised, people often ask with 怎么 instead: 你怎么来了? means “What are you doing here?”

为什么

wèi shén me

why

The first syllable is wèi, fourth tone: wèi shén me.

Ways to say why

为什么
wèi shén me
Everyday
why
The neutral why. Works with anyone: 你为什么学中文?, “Why are you learning Chinese?”
怎么
zěn me
Everyday
how come
For surprise or a small complaint, often with a negative: 你怎么不吃?, “How come you’re not eating?”
干嘛
gàn má
With friends
why; what for
Casual and direct: 干嘛这么早?, “Why so early?”
为啥
wèi shá
With friends
why
Northern and casual. Also common in chats all over China.
凭什么
píng shén me
Everyday
why should I?; what gives you the right?
When you think something is unfair: 凭什么是我?, “Why me?!” It is a protest, not a question, and it can start an argument with anyone.
是什么原因
shì shén me yuán yīn
Formal
what’s the reason?
At work or at a service desk, when you need the cause: a payment that failed, a train that is late.

因为
yīn wèi
because
Start your answer with it: 因为下雨了, “because it’s raining.”
不为什么
bú wèi shén me
no reason
Light and friendly, or to close the topic.
没有为什么
méi yǒu wèi shén me
there’s no why; because I said so
Firm. What a parent says to a child who keeps asking.

Using 怎么 for a plain “why”
你怎么学中文? usually asks how you study Chinese, not why. 怎么 means “why” only for surprise, often with a negative: 你怎么不吃? For a plain why, use 为什么.
Using 凭什么 for a real question
凭什么 asks “What gives you the right?” and starts an argument. To ask for a reason, use 为什么.
Answering 为什么 with 因为…所以
The person who asks 为什么 already knows what happened, so give only the reason: 因为下雨了, or just 下雨了. A full 因为…所以 sentence is correct, but in a quick answer it sounds like a textbook.