A former lecturer of mine once explained why, from a syntactic point of view, the English rule that negation and questions are formed with the auxiliary do follows from other syntactic facts about English.
More precisely, if you gave a good syntactician not familiar with English a corpus of English sentences containing everything but questions and negated phrases, then s/he could infer grammatical rules from it (such as headed-ness of phrases, what kind of arguments what word takes, etc.) From some of these rules, then, s/he could see that something specific would be wrong with the sentences "Gave you the present to Mary?" and "He went not to the cinema."
Can someone explain what exactly this something is and how it follows from other sentences?
FYI, my lecturer did this in Government & Binding with X-Bar theory. This may be more suitable a question for the proposed linguistics.stackexchange.com but as it's not online yet I'm trying it here first.
Edit: the beta is online now at http://linguistics.stackexchange.com/.