“為何”更偏向書面。他們都是一個意思。 為什麽 和 爲什麽 都是對的。為字有2種寫法，都是可以的。

意思相同 區別就在於 中國古代經常用為何 而現在經常用爲什麽 Same meaning ，distinguishes between ancient China often use 为何 ，now often use 为什么

為何 is more written and archaic. in ancient times, chinese used to say 為何, but today we use 為什麽 more. in modern chinese, the most difference is that u can use 爲什麽 alonely, such as:——A says."他说的是对的。”——B wonders, then answers." 爲什麽?" but u can not use 為何 alonely. in the upper example, B can not answer "為何?" if B used, A would think," r u an eld?.." factually, it is rarely that we use 為何 in oral chinese :)

为什么= 为何 为什么不还我的钱？=为何不还我的钱？ 后者，更书面化

Don't be so complex. both of them could use nowadays: 1. they have the same effect while you use them to ask other people,and detail contents followed, example: 为什么这样？ = 为何这样？ 他为什么不愿意？= 他为何不愿意？ 2.when you want to ask why without a detail information , you should only use 为什么. This not means you can not use 为何 at all. but it will be a little unconfortable to the listener coz it sounds like an acient language.