The Novel - how is it defined?

I wanted to say this in class, and yet the idea of contradicting Professor Dimmock wasn't appealing to me. I really enjoyed her visit.

Last semester, I took a class, creatively entitled "the novel," in which, among many other topics, we discussed what it is that actually makes a novel a novel. After reading several thigns that had no plot, no narrative, no coherent characters, and perhaps no artistic merit, we were forced to conclude that a novel is really defined based on it's length. A novel is just a prose (or even a poetry) piece of a reasonable number of chapters. Feel free to disagree with me on that score, but that seems to be how publishers and bookstores are choosing to define it.

The fact that we seem to be able to define an entire genre based on it's length, and nothing else, is a bit bothersome to me. Yes, too much classification and forcing things into boxes can be frustrating, and yet broad categories like "novel" don't seem very helpful. If we're going to classify things by types of work, such as the novel, or a work of poetry, perhaps we should break them down into further, more descriptive categories. For example, can we classify a novel written in prose, and a novel written in verse differently? How about Shakespeare's plays? Are they plays, or poetry? Is everything that is meant to be performed inevitably a play?

And how short is a short story? Where's the line between short story and novella, and between novella and novel? Is it really as arbitrary as I think it is?