One difference is, Socialism wants capitalism and Marxism does not. Marxism believes that capitalism is the main cause for the current conditions.
Therefore, it is safe to say that F. Scott Fitzgerald is a Marxist with the philosophical teaching in all his books.
In The Great Gatsby, Fitzgerald creates an artificial world where money is the object of everyone's desire. The characters, the setting, and the plot are very deeply submerged in a Capitalism that ends up destroying many of them in the end. Fitzgerald's criticism of Capitalism can be seen as a move to subtly promote Socialism, an ideology in which value is placed on the inherent value of an object rather than its market value. Fitzgerald makes Gatsby a novel that is not inherently Marxist or even Socialist, but one that is infused with Marxist theory. He does this by denouncing non-humanitarianism, reification, and market value. Fitzgerald implies that the Capitalist system does not work because at the end of the novel, all of the characters that represent typical American Capitalism end up either dead or completely unhappy. Fitzgerald's criticisms work to warn 1920's Americans of their behavior and how destructive it can be.
Marxists believe very firmly in humanitarianism; they believe that as humans, we should look out for each other and care for each other since we are all on the same level. All of the characters in Gatsby nullify this idea, because they all use each other in one-way or another. For instance, Gatsby uses Nick to set up a meeting between he and Daisy. The characters also place very little value on individual