Question

Olá, eu estava vendo uma música na internet e me deparei com a seguinte frase

"What the hell were we fighting for?"

No caso o What ta sendo usado no lugar do Why. Isso é possível? É usado na fala?

Answer 1

Olá, nesse caso pode usar tanto o "what" como o "why". Porém ao usar o "why", não se deve adicionar a preposição "for" no final, ou a sentença ficará incorreta.

"What the hell were we fighting for?"

"Why the hell were we fighting?"

"For what the hell were we fighting?" (Mais formal)

Answer 2

What for is used when the question is about a purpose, whereas why is used when the question is about a reason.

In your sentence, it has the same meaning as "what was the purpose of our fighting?". Had it been written as "why the hell were we fighting?," the meaning would be "what was the reason of our fighting?"

In short, the difference is in the semantics.