Obviously, someone has to do the writing - the writer. Every writer brings a great deal of knowledge to every writing situation. We know how to form letters (with a pen/pencil or with the right key on the keyboard); we know how to shape grammatical sentences; we know about the topic we want to write about. Every writer also brings less obvious knowledge to the writing situation. We know when certain words might be offensive so we shouldn't use those in certain kinds of writing; we know from our own reading experiences that readers expect certain kinds of arrangements of material on the page; we know that e mail differs radically from a formal academic paper. In other words, as writers, we know a great deal about the language itself that we will use to construct the specific sentences, paragraphs, and text overall, and we tacitly know about formality (called register), types of formats (called genres), and cultural conventions for writing. But this latter kind of tacit knowledge can be slippery because we may not be aware of how much we know, and thus we may not think that knowledge is as important as the school-emphasized knowledge from writing classes.