How to say "why?" in Chinese

为什么 is a compound of 为 (wèi, 'for') and 什么 (shénme, 'what'), literally 'for what'. It functions as a single interrogative adverb meaning 'why'.

Use 为什么 to ask for reasons or causes. It's neutral in tone and works in any situation. In casual speech, you can also use it alone as a one-word question. Be aware that in Chinese, the question word often stays in place rather than moving to the front, so you might hear '你为什么要走？' (why do you want to leave?) with the subject before 为什么.