Essayist: Some linguists claim that competent speakers of a language have explicit knowledge of the rules of grammar for that language. However, linguistic ability is not the possession and utilization of a body of knowledge, or rules of grammar, but is more similar to a skill like riding a bicycle. Just as the typical cyclist does not need to know physics, neither does the language user need to know grammar rules.
There is a difference between knowing a set of rules and behaving in accordance with a set of rules most accurately expresses a principle underlying the essayist's argument.