Although the novella is short and spare, Steinbeck's Of Mice and Men explores major themes of loneliness and alienation, dreams versus reality, and friendship and loyalty. These universal themes are revealed through Steinbeck’s detailed characterization and succinct and graceful prose.

Loneliness and Alienation

Steinbeck explores the theme of loneliness and isolation through specific character interactions. For instance, Candy, Crooks, and Lennie all exemplify the experience of alienation.

Candy is an aging and disabled ranch hand who has been relegated to cleaning the bunkhouse. Due to his age and physical disability, he cannot participate with the other men in ranch work and is excluded by the men when they visit the town. Steinbeck uses Candy’s old dog to parallel Candy’s own advanced age and diminished ability on the farm. Despite Candy’s reservations, the other ranch hands advocate for killing Candy’s dog, whom they believe is too old to be useful anymore. The ranch hands view Candy as being just as useless as his old dog, representing how the farm treats its own members once they've outlived their purpose. The men can exercise the power of putting the dog “out of its misery,” which is something they cannot exercise over Candy.

Crooks embodies the isolation and loneliness that arise from racial differences. As the only African American on the ranch, Crooks is ostracized and mistreated. At the time of the Great Depression, when Of Mice and Men is set, African Americans experienced a great deal of racism. Crooks exhibits an understanding of this; he realizes how and why he has been alienated from the other men. When Crooks and Curley’s wife get into a disagreement, Crooks’s belief that he can partake in the dream of owning land is dashed. He is quickly broken down again by Curley’s wife’s threats against him. Crooks sees that living in isolation is safer than interacting with the white men and women, whom he obviously cannot trust, because they will inevitably mistreat him.

Lennie faces the fear and stigma attached to having a mental disability, and we see the reverberations of this alienation throughout the novella. Although Lennie is cared for by George, he is misunderstood by many who encounter him, such as Curley’s wife. Lennie doesn’t wish to hurt anyone, but he lacks the social knowledge and physical control to avoid doing so. Lennie is left out of activities such as going to the town with George and the other men. However, Lennie also stands as a foil to loneliness through his absolute loyalty and friendship to George.

Dreams versus Reality

The clash between the lure of dreams and the harshness of reality is a major theme in Of Mice and Men. Lennie and George hold on to their version of the American dream: owning their own piece of farmland. Steinbeck shows how the American dream is an ideal that is impossible—or at least very hard—to attain. For Lennie and George, their shared dream dissolves when Lennie accidentally kills Curley’s wife.

However, the dream is present throughout the novella, attracting the most isolated and desperate characters to begin, if only momentarily, to imagine a better life for themselves. Candy, who is physically disabled, aged, and almost useless on the ranch, takes comfort in George and Lennie’s dream and even offers to put his life’s savings toward it. Crooks, who is alienated for being an African American, takes comfort in the dream and imagines himself working alongside others. Lennie and George’s dream is to “live off the fatta’ the lan.’” Such land ownership and control of natural resources stands at the very core of the American dream. Last, for Lennie, the ideal future is one in which he owns rabbits on the land that he can take care of and pet, which is his strongest desire throughout the novella.

This dream also stands in juxtaposition to the Great Depression. The Great Depression was marked by a dire scarcity of land and wealth for the majority of Americans. For Lennie and George, life as itinerant workers means unsteady pay, unsteady work, and an unsettled life. It is hard for these two men to create savings with the low wages they are given.

Given that George and Lennie are job searching during the Great Depression, finding work is made even more difficult by the lack of job opportunities. Further, Lennie’s mental disability puts a strain on George as a caretaker. Lennie is presented as a character who is both George’s partner but unable to function on his own. Lennie’s innocence and mental disability stop him from being able to care for himself. Lennie’s innocent and simple state either cannot exist or will struggle to exist in society. Since Lennie kills Curley’s wife and is then killed in return, this suggests he is a danger to both himself and others and that there is no place for him in the current system. Similarly, the dream in its idealism and innocence cannot exist in reality either. For Lennie and George, the dream of owning their own space is a source of comfort and happiness. The dream represents an escape; however, their circumstances make their dream a nearly impossible goal to attain.

Friendship and Loyalty

The theme of friendship and loyalty is most clearly seen through the relationship between George and Lennie. George is Lennie’s caretaker, and although George openly admits to feeling trapped by his responsibility to Lennie, he refuses to leave Lennie to fend for himself. Lennie, in turn, shows a huge amount of loyalty towards George.

George had at first taken advantage of Lennie’s mental disability, but he realized that Lennie’s loyalty to him knew no bounds. When asked to jump into a river by George, Lennie did so, despite not being able to swim. Although George meant the request as a joke, it almost killed Lennie. George learned to stop messing with Lennie after that, because he realized his responsibility in the face of Lennie’s enormous trust in him.

George later shows his friendship and loyalty towards Lennie after seeing that Lennie has accidentally killed Curley’s wife. George understands that Lennie’s fate is either to be lynched by the ranch hands or to be locked up in an asylum. He knows that either end results in great suffering. George chooses to kill Lennie himself—quickly and humanely—after soothing Lennie with wistful reflections about their dream. Thus, Lennie’s final thoughts are joyful. Although a morally questionable action and possibly problematic commentary towards mental disability, George’s decision to kill Lennie reflects his loyalty and love for his friend. George chooses to end Lennie’s life in the best of circumstances, rather than let Lennie fall into the uncaring hands of the other men.