On the formal argument that Boyhood (2014) makes about cinema and time.

Richard Linklater shot Boyhood over twelve years, using the same cast and allowing the actors to visibly age across the film. This is not a documentary technique. It's a fiction film using documentary time.

The formal achievement is that you believe in Mason's childhood not because of the performances or the writing, though both are excellent, but because you are watching time actually pass. The child you see in the first hour is the adult you see in the fourth hour. This is true in a way that makeup and casting changes cannot be.

What Boyhood loses by this technique is some degree of narrative control — Linklater had to work with what the actors and time provided. What it gains is irreplaceable: the experience of watching a specific human being grow up, with all the contingency and incompleteness that growth involves.

The film is controversial in cinephile circles partly because it's accessible and partly because its formal achievement is visible and describable. Easy formal achievements make people suspicious. Boyhood's achievement is simple in concept and technically impossible to replicate.