Question on Main Point - Metaphors Question Stem

Hello! I got the answer right for this LR question, but was having a hard time unpacking the last sentence of the prompt. I know starting with "for unless" is a premise but the wording is a bit convoluted.

"Some extremists claim that all uses of language are metaphorical. But this cannot be so, for unless some uses of words are literal, there can be no nonliteral uses of any words.