Ambiguity - can the writer leave it up to the viewer?

I recently read a script with supernatural elements. Or were they? I wasn't sure if all the mad stuff that took place was real or not. The writer himself, when questioned, felt that the story operated on several possible levels - that the happenings in the script were supernatural or that they were caused by malevolent real people. He wasn't sure which it should be, and wondered if he had to even make the decision. Couldn't he just leave it up to the viewer to decide?

My opinion on this: yes, the viewer can decide for themselves, on watching the movie, what's actually going on. BUT - the writer must make a decision at an early stage of writing the film (this was a first draft) what he/she thinks the solution is. The writer, of all people, must be sure of what's happening! David Lynch knows what's going on in all his films, trust me - even if no one else does!

Take control of your story and make the call about which direction it's going in. Because otherwise, you are headed for a seriously vague mess of a final product, and we've all seen way too many of them....