Jacques Rivette's "La Bande des quatre" (1988)
Not only a "double inconstance" ("double inconsistency") but infinite of them. "Il y a des choses derrière les choses" ("There are things behind things") in Jacques Rivette's La Bande des Quatre (English title: Gang of Four).
Consciously and wisely artificial, the line between acting and reality is never even drawn. There are no clear meanings, not a theme you can put your finger on, but a simple question such as "Coffee?" has such infinite weight that it can easily bring tears, tears coming from somewhere I didn't even know existed.
Just as in theatre, in cinema, or in life, it's impossible to know where the truth, or the beauty, lies. But in La Bande des quatre the answer is given by Constance (first in original French, then my English translation):
"La démolition. C'est avec ça que vous avez à faire. Tout le temps. La démolition et le doute... C'est avec ça que vous devez construire, créer, inventer..."
"Demolition. That's what you have to do with. All the time. Demolition and doubt... It's with these that you have to build, create, invent..."
In Rivette's case, what results is a free cinema, liberating the mind, and the eyes, forcing the viewer (the participant) to understand a new way of composing the world, a whole new restructuring...
La Bande des quatre might easily be the most wonderfully acted film I've ever seen, each actress (or actor) constantly creating wonders, certainly helped by Rivette's free mind.