The tune of "As Time Goes By" is one of Casablanca's most important themes, but the words are sung only on two occasions. Sam sings the first two verses at Ilsa's request on the night of her arrival with Laszlo in Casablanca. Rick, who has forbidden the song in his bar, reacts angrily, but he catches sight of Ilsa just as he begins to reprimand Sam. The song becomes the occasion of their re-acquaintance. Later, Sam sings the last two verses during Rick's Paris flashback. As the song plays, Ilsa and Rick stand beside the piano and Rick fills glasses with champagne. Ilsa is noticeably distracted, and presumably she has already learned that Laszlo is still alive. Rick casts a glance at Ilsa that suggests he knows something is bothering her, but he doesn't mention it in the dialogue that follows. In this case, the song marks a missed opportunity to tell the truth and prevent years of resentment.

The actual lyrics of "As Time Goes By" are also significant, since the message of the song suggests that the world is a complicated place full of continuous change, but that one thing remains constant: timeless, enduring romantic love. Casablanca does not accept these words at face value but puts them to the test. The passing of time is one of the film's main themes, and the question of whether love endures is one of its central questions. Before Ilsa shows up in Casablanca, Rick seems to have given up on the possibility of a pure, timeless love. Ilsa's confession of love in his apartment complicates the picture, but at the movie's finale, time, not love, triumphs. Time and history, in the form of the war, dominate the present and steer the future. If the love between Rick and Ilsa does survive, it will do so only as memory. The significance of the words of "As Time Goes By," therefore, is that they are ultimately false. The future can and does bring situations that interrupt love, and the fundamental things don't always apply.

Rick and Ilsa exchange these words in Rick's flashback to their time together in Paris. Rick remembers this exchange the night he first sees Ilsa in Casablanca, as he drinks alone late at night in the empty bar while Sam plays "As Time Goes By." Rick remembers the days in Paris as idyllic and untroubled. The war had not yet come to the city, and Rick believed he had found true happiness with Ilsa. In the flashback, Rick is lighthearted and smiling, a person altogether different from the heavy brooder we see in Casablanca. In this dialogue, Rick wants to know all about Ilsa, but she rebuffs his questions by reminding him that they agreed not to discuss each other's pasts. This agreement protects the innocence of their relationship, but it also prevents Rick from learning the truth about Ilsa, which might have saved him years of heartbreak. Although the war has not yet come to Paris, it has already spread to Czechoslovakia, where Ilsa's husband, Laszlo, was arrested, sent to a concentration camp, and, she believes, killed. The past is too painful for her to think about, and she most likely also fears Rick's reaction to the news of her marriage.

In Casablanca, whenever Ilsa tries to explain to Rick what happened in Paris, she points out that they knew very little about each other. In effect, this reminder becomes her excuse for the emotional pain she caused him, but it is also a rebuke to Rick. She intentionally maintained his ignorance about her. At the same time, had Ilsa answered honestly, the whole tone of the memory would be different. Ilsa and Rick's simple love would be turned on its head. Rick seems to have a choice: a painful present and a perfect memory, or a complicated understanding of both. As he remembers the Paris days, Rick seems to prefer to keep the memory pure. But eventually he embraces the truth about his time with Ilsa both in Paris and in Casablanca, which is necessary if he is going to move on with his life. He recasts the memory by repeating the line "Here's looking at you, kid" at the end of the film.

Louis makes this announcement in Rick's after the patrons' spontaneous rendition of “La Marseillaise” angers Strasser and he demands that Rick's be shut down. Louis must find some excuse to carry out the order, and gambling is what he comes up with. Louis is the film's great wit, and this is probably his best line. He delivers it with a straight face—then politely accepts his gambling winnings from that evening. Louis brings levity and comic relief to an ensemble of intense, brooding characters: Laszlo, the passionate politician; Ilsa, trapped in a heart-wrenching conflict; Rick, the silently suffering sentimentalist; and Strasser, the determined villain. In Casablanca, not all characters suffer from the anxiety of the war, and Louis lives a pleasant life of easygoing hedonism and harmless corruption.

Petty crime is everywhere in Casablanca, and this line serves as its official stamp of approval. It also reveals something fundamental about Louis's character. A gambler himself, he has known for some time that gambling takes place at Rick's. Not only does Louis shut down Rick's with his deadpan announcement, but he also effectively reminds us that he always could have shut down the bar in the past, but never did. Ironically, by flexing his muscle at this moment, and at the request of Strasser, Louis shows where his true loyalties lie. Had Strasser not said a word, Louis would have done nothing, as he always had before. Moreover, Louis knows that gambling is not the only illegal activity to go on at Rick's. Rick's is also a place where stolen letters of transit are sold and where members of the underground resistance meet to discuss their plans without arousing suspicion. That Louis uses gambling, rather than political activities, as the excuse to shut down Rick's is significant. Louis's eventual rejection of Vichy and collaboration is anticipated by this statement. At the height of Louis's moral hypocrisy, he reveals the seeds of his political idealism.

Rick says these words to Ilsa at the airport during the final scene. As the scene unwinds, who exactly will depart Casablanca that night and which man, Rick or Laszlo, will wind up with Ilsa remain unclear. Just before Rick says these words, he states clearly his decision: Ilsa and Laszlo will leave together on the plane, and Rick will remain in Casablanca. With these lines, which culminate the most dramatic exchange of dialogue in the film, Rick recasts the entire question. The real concern, he suggests, is not which man will get the woman. In the larger scheme of things, such a concern doesn't matter. A war is raging is Europe, and the happiness of these three people is insignificant.

These lines are the clearest statement of Casablanca's moral resolution: the triumph of the political over the personal. But Rick is saying more than just this. Although Rick calls himself, Ilsa, and Laszlo "little people," he also recognizes that Laszlo is something more. These lines are not a cry of despair but a recognition of the fact that large political considerations trump the individual concerns of lovers. Laszlo must survive in order to continue his political work. Ilsa must accompany him, not necessarily because she loves him, but because he loves her, and her presence will make him more effective politically. Through the personal sacrifice these words imply, Rick catapults himself from the realm of "little people" into the sphere of large causes. Like Laszlo, Rick becomes a partisan, a warrior, and a hero, and he seems to realize that whereas Laszlo's heroism is amplified by Ilsa's presence, Rick himself functions best on his own.

While Rick claims heroism for himself with these words, he denies the same privilege to Ilsa. Rick claims to have learned that their love means nothing, but Ilsa, he says, can't understand that yet. Only in the future will she figure it out. At best, her actions are passively, or accidentally, heroic. Those who see Rick as exacting some sort of revenge against Ilsa in the finale will find some proof in this scene, as Rick seems to write off as insignificant or foolish any heartbreak Ilsa may feel. He, of all people, should understand how devastating a broken heart can be, and in asking Ilsa to calmly accept and understand his decision, he is asking the impossible. Rick tries to comfort the heartbroken Ilsa with the words "Now, now," but he also calls attention to their differing priorities. She still believes in the importance of love, while he understands that some things are even greater. Shortly after this speech, Rick tells Laszlo that Ilsa visited him the previous evening and pretended still to be in love with him to get the letters. Rick prefers the certainty of being noble to the uncertainty of love, despite the ambiguities of each person's true feelings. In making the choice to let Ilsa go, he rebukes Ilsa, who, unlike Laszlo and Rick, seems still to consider love the higher value.

At the speech's finale, Rick repeats his favorite phrase of affection: "Here's looking at you, kid." The repetition of this phrase, like the consoling words "Now, now," suggests that love continues to endure, despite the circumstantial barriers that keep Ilsa and Rick apart. At the same time, the phrase takes on a new resonance. "Here's looking at you, kid," when Rick said it in Paris, implied a childlike sense of an interminable present, when the looking promised to last forever. The playful "kid" at the end suggests the innocence of Rick and Ilsa's love. In this final statement, we understand Rick to be saying, "Here's looking at you for the last time." The "kid" comes across as ironic, for the events of the past two years have forced both characters to see the world for what it is, a lawless and often hostile place that leaves no room for childish innocence or ignorance. Rick is not only saying goodbye to Ilsa here, but to the child within himself. His act of self-sacrifice is his political coming of age, just like that of his nation as it decided to enter World War II.

This sentence, spoken by Rick, concludes Casablanca. Rick says this to Louis after the plane carrying Ilsa and Laszlo to Lisbon has departed, Strasser has been killed, and Louis has abandoned his cynical neutrality to embrace the Allied cause. As Louis and Rick walk side by side down the airport's empty runway, we see that their fates are linked, most overtly in their shared decision to leave Casablanca for Brazzaville, in French Congo. Their fates are linked in other ways as well. On the one hand, friendship with Louis is a consolation to Rick after Ilsa's departure. However, the words speak of hope, not resignation. Both Rick and Louis have earned a new beginning. The friendship between Louis and Rick is not itself new, and their mutual affection has been evident throughout the film. Rick's calling this a "beginning," therefore, implies that the terms of the friendship have changed. Whereas the two were once joined by bonds of self-interest and generally interacted out of necessity, now they share a political bond. Political idealism, in the form of active resistance to Nazi rule and the consolidation of the American-French alliance, has replaced casino kickbacks as the cement of their relationship.