Grammar is used to refer to a number of different things: it can be used to refer to books that contain descriptions of the structure of a language; it can be used to refer to the knowledge that a native speaker has of his or her language and to descriptions of that knowledge; it can be used to refer to a set of rules developed to control certain aspects of the usage of native speakers; and it can be used to refer to a set of rules typically taught in school about "appropriate usage" and about writing.A descriptive grammar looks at the way a language is actually used by its speakers and then...