Dave is stuck between boyhood and manhood and feels his manhood is threatened throughout the story. In order to become a man, gun will help him reach his responsibility. The coming of age is a major theme.
Racism is also a theme in the story as Dave was excluded from the social order. Dave struggles to seek Power which is another theme of the story. He does not want to be treated like a boy so he wants to own a gun which symbolizes masculinity, adulthood and power. Lastly, the Mule symbolizes responsibility.
