"We are familiar with the Aristotelian distinction between “verisimilitude” and “the necessary.” Corneille speaks of this in his Discours and applies it to the action, but not without extrapolating. Extrapolating in turn, we shall allow ourselves to apply it to the text and shall say: Everything in the text that is indispensable to the clarity of the intrigue is necessary. All that the characters say among themselves in a given situation that is not concerned with informing the audience is verisimilitude. For example, in Racine’s Andromaque, the fragment of the first verse, “…since I find such a faithful friend again,” is absolutely necessary (it informs us that Orestes and Pylades are friends and were separated) but not very true to life, as the interlocutor does not need this information: It is meant only for the reader. The “yes” that beings the verse makes the rest of the sentence seem like the continuation of a conversation that has already begun and is there to provide, among other things, the verisimilitude that is lacking.
“Thus, we see that in theater, the necessary takes precedence over verisimilitude and that its presence, even diffused, limits the sphere of the true-to-life. A film’s dialog, on the contrary, must use the necessary only as a last resort. Information is presented in an inoffensive manner, cloaked by pure verisimilitude. It reaches the attentive spectator, whose vigilance increase as he learns more, by a ricochet effect. Film dialogues from before 1960 seem unencumbered with necessary lines that modern film has left as commentary, monologues, or graphic signs, with an ease that is beginning to seem dates as well.
“Nothing goes out of style more quickly than the necessary—except verisimilitude, whose excess in the 1970s is beginning to show. In order to give free rein to the true-to-life, we have done away with written texts and have actors say “just anything.” It was believed that from this absolute contingency, a new necessary would be born, without any reference to the “rules” of the theater that were always lurking in the background. It did happen, sometimes felicitously, with Rouch, Godard, or Rivette. The true killed the true-to-life: The stopgap realism of the scriptwriters become unbearable. And here we are once, again, faced with the demands of the necessary."
---From “Film and the three levels of discourse: indirect, direct, and hyperdirect” by Eric Rohmer, Cahiers Renaud-Barrault 96, October 1977.
Thanks to Danny for finding this for me.