A compelling script by Julius and Philip Epstein and Howard Koch, Michael Curtiz’ sleight-of-hand direction that cunningly diverts attention from weaknesses of plot, and above all, the miraculous pairing of co-stars, arguably make Casablanca Bergman’s best – and certainly most cherished – film.
Luminously feminine, Nordic Bergman and swarthy, American tough-guy Bogart went far beyond being merely a pair of screen lovers professionally fulfilling front-office hopes for a box-office bonanza. Together, they created two unforgettable individuals whose interaction never fails to fascinate.
For all Bogart’s burly brusqueness, he projects persuasively the world-weariness of an intellectual idealist turned sour.
Bergman, on the other hand, has the more difficult role, that of a vulnerable woman desperately torn between emotion and duty. Her former lover, Bogart, has changed, choosing to live for the moment and letting those destroy themselves who will; her husband, Henreid, is a passionately dedicated anti-Nazi idealist. That Bergman’s ardent portrayal projects believably and humanly the turmoil of being attracted to these opposite temperaments is testimony to her trained skill and great strength as an actress. In no other role has she demonstrated so well her ability to suggest a woman of romantic susceptibility who also has a strong sense of ethical commitment.
The Bergman-Bogart chemistry works because they persuade us that two intelligent sensibilities, drawn to one another in an adult love affair, have become alienated by events they cannot control. Bergman discussed the difficulty of working with an improvised script during the filming of Casablanca. She recalled that the cast frequently would not know what their lines or situations would be from day to day, and that none of them knew how the tangled plot would be resolved until the final scene was shot. Doubtless, the tentative atmosphere contributed to the actors’ convincing depiction of the characters’ uncertainty as to what is to become of them. (None of these incidental script problems prevented the authors from receiving a joint Academy Award for that year’s Best Screenplay.)

Curtis F. Brown, Ingrid Bergman, Pyramid Publications, New York 1973