Writer or Author?

I understand we will be talking about this in class tomorrow, but I wanted to get some thoughts out there before. In class there was a distinction made between writer and author, a distinction, to be candid, I do not fully understand. As such, my comments are, more so than usual, an invitation for correction. It seemed clear that the writer was the person, the individual who composed the work in question. This includes, naturally, all the boring details of biological and biographical information. The author, I was slightly unclear about. I understand that Nehemas spoke of a postulated author as a hypothetical version of the writer that possessed the answers to all possible questions regarding the text. Is this the sole meaning of author we are using? Corey suggests that the author means: "the intentional agent who at the time of writing the work, has the motive of communicating something specific through the literary work." This seems to be a perfectly reasonable definition of author, but I fail to see how it should be distinct from the writer.

It seems that the distinction between writer and author is rather contrived and unhelpful.