As we identify in the "Classic Plot Analysis," one main conflict in The Catcher in the Rye is that Holden judges and decides he hates nearly everyone, but at the same time is lonely and needs to forge personal connections with others. This is quite a conundrum, and we see the same scene play out over and over: 1) Holden meets a person. 2) Often, but not always, Holden judges the person to be a "phony," a "moron," or a "pervert." 3) Holden tries to reach out to that person anyway, usually by asking them to have a drink with him. 4) The person refuses.
All the people Holden attempts connections with are similar in this way, so they're all foils for one another. To be specific, we're talking about Ackley, Mrs. Morrow, nameless cab driver #1, Faith Cavendish, Bernice, Marty, Laverne, cab driver #2 (a.k.a. Horwitz), Sunny, the two nuns, Sally, the little girl with the skates, Carl Luce, Valencia, Valencia's piano-player, the hat-check girl, the secretary at Phoebe's school, and countless others.
To take a specific example of the principle, the scenes that play out between Stradlater and Holden and then later between Maurice and Holden are foils for each other. In each instance, Holden is wronged, forces the issue, is threatened, given an opportunity to back down from a much stronger opponent, cries, insults the much stronger opponent's intelligence, and ends up getting socked. We think these two scenes are getting at Holden's self-destructive tendencies. Or maybe just his inability to let sleeping dogs lie.
Again, we're talking more about the scenes with these characters than the characters themselves. The Holden-Spencer conversation and the Holden-Antolini conversation mirror each other structurally – they're the book-ends to the novel, so to speak, one at the very beginning, one near to the end. Both feature a former teacher berating Holden for not taking education seriously. Both revolve around a strange physicality: with Mr. Spencer, it's Holden's visceral awareness of the man's body and its appearance; and with Mr. Antolini it's the physical contact between the two characters.
But being foils and all, there are some differences, too. Mr. Spencer's lecture is an alienating and actually rather annoying rant. When Mr. Antolini starts talking, we sort of expect the same thing. We're surprised to see that he actually has some real insight into Holden's character – and some real advice to offer him. Are the two teachers very different, or has Holden evolved over the course of the novel so much that he's now able to hear and accept help instead of rejecting it – and therefore presenting it to us – as phony and irritating? Good question.