Writing is really nothing more than setting down on paper what we would otherwise speak with our mouths. It would be impossible for a man to be a great speaker and a poor writer because all he needs to do is write down that which he would speak.
His main point is that knowledge of grammar, logic, and rhetoric should be enough to teach one to write. You don't need a separate course. I wonder, though, whether he overstates his case somewhat that there is no distinct art of writing that has its own rules. For instance, a well-written sentence isn't always as effective when spoken, as those who try to proclaim a literary translation of the Bible in liturgy have discovered.
Any opinions? Class, discuss!