Steinbeck uses a number of motifs throughout the novella to heighten its intensity and impact. These recurring devices symbolize elements of the major themes within the book. One of these supporting devices is borne out in Steinbeck's unflattering depiction of women. They are represented as corrupting influences who are unnecessary --- and perhaps even undesirable --- for building a happy life, most obviously represented in Curley's wife. The motif of strength and weakness --- for example, Lennie's physical strength and mental weakness --- is also prevalent.
The themes Steinbeck explores in "Of Mice and Men" are very dark. Each character experiences, in different ways, loneliness and isolation and seems to be reaching blindly for true companionship and relationship. From this theme grows the even darker concept of the parasitic and predatory nature of humanity, as each character --- no matter how innocently --- uses the others for his own betterment or comfort. Steinbeck also portrays desperation in the overarching theme of the inevitable impossibility of paradise and the American Dream. One of the more positive themes is that of fraternity, powerfully evidenced in the loving relationship between Lennie and George.
Throughout the novella, Steinbeck foreshadows the grim events to come. When Candy lets another man put his faithful dog out of its misery, he expresses sorrow, using words that indicate that George will have to take responsibility for putting Lennie out of his misery in a way Candy did not. When Lennie accidentally kills a puppy, Curley's wife walks in, foreshadowing her own demise at Lennie's hands.
Steinbeck uses dialogue powerfully throughout the novella as a vehicle for his themes and motifs. Many characters speak with intense cruelty to one another, representing the ugliness of human nature. Lennie's gentleness and weakness are similarly represented through dialogue.
Steinbeck deftly uses symbols throughout the novella to speak to his broader themes. George and Lennie's dream farm represents their pursuit of both the American dream and fraternity, as they seek to create an insular world where they can be happy together and Lennie can be safe from outside influences. Lennie's puppy, which he accidentally kills, represents the struggle between strength and weakness; it dies because of Lennie's overpowering strength, but also because of his weakness, as he failed to realize he was harming it. Candy's beloved dog also represents the social aspect of the novel and its controversial euthanasia theme, symbolizing the necessary end of those who have outlived their own purpose.