  These insights were to drive linguistic theorizing for the next fifty years, and it's worth emphasizing just how radical and exciting they  were at the time. First, the idea that explaining language use  involves attributing knowledge to speakers flouted the  prevailing behaviorist view that talking about mental states was  unscientific because mental states are unobservable. It also raised  several pressing empirical question that linguists are still  debating. For example, what is the content of speakers'  knowledge of   language?[3]  What sorts of facts about language are represented in speakers'  heads? And how does this knowledge actually function in the  psychological processes of language production and comprehension:  what are the mechanisms of language use?