The theme of loneliness is a dominant theme in the novel. John Steinbeck exhibits it through characterisation. Although present in all the characters to some degree, loneliness is most notably present in Candy, Crooks, and Curley's wife. They all fight against their isolation in whatever way they can.
Candy is one of the characters who experiences loneliness. This is brought about after the death of his dog. Candy's dog was his only companion and stopped him from being alone in the world. After its death, Candy struggles against loneliness by sharing in George and Lennie's dream. However, this all comes to nothing when Lennie kills Curley's wife. Candy's disappointment is expressed in the bitter words he utters to Curley's wife dead body, whom he blames for spoiling his dream. As he says at this point in the novel: "You done it, di'n't you? I s'pose your glad. Ever'body knowed you'd mess things up.
You wasn't no good. You ain't no good now, you lousy tart".
Besides Candy, Crooks also suffer from isolation. Being black, he is not allowed in the bunkhouse with the other men; he has "his bunk in the harness room". Loneliness has made Crooks unfriendly and has formed bitterness towards everyone. When Lennie comes into his room, his first reaction was in fact one of hostility. In this part of the novel, Crooks's emotions are displayed where he tells Lennie about having no one to relate to and communicate with. "S'pose you didn't have nobody. S'pose you couldn't go into the bunkhouse and play rummy 'cause you was black." Although he spends much of the time reading books he "needs somebody - to be near. A guy goes nuts if he ain't got nobody. Don't make no difference who the guy is, long's he's with you. I tell ya a guy gets too lonely an' he gets sick."
Perhaps the loneliest character, which Steinbeck creates in the novel, is Curley's wife. She is the only female on the ranch and although she is married, her husband does not give her the attention, which she desires. Therefore, she seeks it among the men on the ranch by acting flirtatious, the way she dresses and her heavy make-up. However, the workers want anything to do with her because she means trouble. When Lennie was in the barn, Curley's wife comes along trying to convince Lennie to speak to her. Curley's wife remarked, "Why can't I talk to you? I never get to talk to nobody. I get awful lonely." She speaks about her disappointments in her life. Lennie was not listening or taking interest in what she was saying, he was only hearing. This did not matter for Curley's wife; having someone there was enough for her.
Friendships and unconditional love could have prevented such isolation of each character. Loneliness has affected each person differently, but the source of changes within the personalities is the same. Steinbeck uses George and Lennie as a contrast to the others because just as Lennie said, "I got you to look after me and you have got me to look after you and that's why". However, the friendship dies with Lennie's death and from this stage onwards, George is a victim of loneliness just like the other ranchmen.