Why can't we go?
We use the words what, which, why, where, who and how to introduce questions. The word order changes when we use them. When the main verb is to be, it comes after the question word (e.g. what is that?). For other verbs, we use an auxiliary (e.g. do, have)
We usually use how to ask about the way something is done, but we can use it with other words to express different ideas, usually to quantify things:
|When to use 'what' and 'which' in questions.||BBC Learning|