> Doug distinguishes between "commercial" and serious" ambiguity.
I don't think that commercial or uncommercial is the relevant distinction here. The question is whether the text includes cues (or even just clues) that lead the audience to think one way or another. Brokeback Mountain has such cues: the audience hears what Jack's wife says, and then the audience is shown Jack getting beaten up; the point of view of the latter sequence -- whether it's an omniscient view or Jack's mind's eye -- is not clarified to the audience, which is a cue to think of a specific kind of ambiguity, i.e., an inability to decide between the two alternative interpretations.
Now, compare Jaws and Gojira (< http://www.imdb.com/title/tt0047034/> -- the recent American Godzilla is a spinoff of it). Both are commercial, but the latter includes a clue that it wants to do something more than simply scare the audience by making the monster a product of atomic testing, whereas the former doesn't include any clue like that. Why and how did the shark become so monstrous, single-mindedly pursuing its human preys? The film doesn't say anything about that.
Or you can compare Jaws with Poltergeist (co-written by Spielberg), again, both commercial. Unlike Jaws, Poltergeist includes an explicit cue to criticize unchecked real estate development that stops at nothing and even the history of dispossession of American Indian lands (see <http://www.filmsite.org/polt2.html>).
Yoshie Furuhashi <http://montages.blogspot.com> <http://monthlyreview.org> <http://mrzine.org>