Why Do We Have Grammar

[?] may seem like a nuisance to study, but it surely helps us to [?] ourselves better and more accurately. Would not be nice if we could just speak and write as we like, without having to learn the [?] of grammar? Of course no.
Actually, if everyone spoke and wrote perfect [?] and everything we heard and read was expressed in perfect, accurate English, we probably would not need to study grammar. Grammar [?] us what corrections we should make in our speech and writing. The [?] of grammar helps us to improve the way we express ourselves by using English which is accurate, clear, varied, and [?].