The purpose of Steinbeck's inclusion of Candy and Curley's wife in Of Mice and Men is to further develop his theme of idealism versus reality. It is a theme that dominates the novella.
The theme of idealism versus reality is a major part of Lennie's and George's characterization. Lennie wanting to "tend the rabbits" and George wanting a place of his own so that he can be his own "boss" is what motivates both of them. Steinbeck broadens this idea and applies to many of the characters in the novella. Candy and Curley's wife are two examples of this. In doing so, Steinbeck universalizes the idea that individual dreams often crash into reality in life.
Curley's wife had dreams. At one point in time, before she became "Curley's wife," she dreamt of stardom in films:
’Nother time I met a guy, an’ he was in pitchers. Went out to the Riverside Dance Palace with him. He says he was gonna put me in the movies. Says I was a natural. Soon’s he got back to Hollywood he was gonna write to me about it...I never got that letter...I always thought my ol’ lady stole it. Well, I wasn’t gonna stay no place where I couldn’t get nowhere or make something of myself, an’ where they stole your letters.
Curley's wife is included because she is an example of someone's identity being linked to dreams. In this way, she is similar to Lennie and George. Like them, she represents how reality has a way of bringing down dreams. The humanity in Curley's wife is brought out when we realize that her dreams are broken. Steinbeck includes her in order to advance the theme of idealism versus reality. As with so many in the novella, she ends up being crushed by the weight of her own dreams.
The idealism versus reality theme is significant to Candy as well. The old swamper has little in his life when Lennie and George first meet him. His dog is the only real thing to which there is affection, something that Carlson addresses in his own way. When he overhears George and Lennie talk about their dream, Candy sees his own idealism emerge: "Maybe if I give you guys my money, you’ll let me hoe in the garden even after I ain’t no good at it. An’ I’ll wash dishes an’ little chicken stuff like that. But I’ll be on our own place, an’ I’ll be let to work on our own place.” Candy's dreams ends up giving him purpose. Even at the end, when George knows his dreams are over, Candy asks if they can still pursue their dreams together. Candy's inclusion in the novella is another reminder of how idealism versus reality is a defining part of human identity.
Steinbeck once said that it was important to "try to understand man." In trying to understand human beings, Steinbeck introduces us to characters who struggle with idealism in the face of reality. Candy and Curley's wife are two of the several characters in Of Mice and Men that we get to know because we know of their dreams and the struggle of trying to achieve them.