Here you will find a description and explanation of the major themes from Joseph Heller's Catch-22.
Brave New Bureaucracy
Have you read 1984? Written in the aftermath of the Second World War and set in a grim "future," this novel by George Orwell portrays a society completely at the mercy of its bureaucracy. Microphones, video cameras and neighbors all become tools of the state in enforcing not only obedience in action, but obedience in thought as well. The main character of the novel, for example, is responsible for changing the journalistic archives of the past to ensure that the historical record only contains what the government wants it to contain. The leader of his society, Big Brother, never appears except in posters. The true source of authority comes from thousands of agents sitting at thousands of desks, pursuing thousands of "dissidents" in maintaining enough fear to keep the "proles" (commoners) content and quiet.
One of the primary themes from Catch-22 appears in the fact that the men in Yossarian's squadron do not have the freedom to choose whether or not to die; in fact, most of the decisions do not come from one individual. Instead, they come from an invisible bureaucracy that operates with no discernible sense of purpose. Even though the Allies have already come close to vanquishing Germany, the men at Pianosa must still fly more and more combat missions -- even though their necessity is unclear.
The menace of the bureaucracy appears in several interrogation scenes -- that of Clevinger and that of the chaplain. The chaplain's interrogators do not even know what he did wrong: they are hoping that he will slip up and tell them. Clevinger does not get to establish his innocence, because Scheisskopf keeps reprimanding him for his syntax. When Yossarian is menaced by a mysterious man who says he has taken Yossarian's "pal," the insidious ways in which this organization can menace the individual take a monstrous turn.
The bureaucracy also has a comic side, though, as Yossarian's adventures as a letter censor show. His forged signatures as "Washington Irving" and "Irving Washington" tie the organization up in knots.
The Spectre of Death
After the death of Snowden, Yossarian's primary objective changes from serving the U.S. military to preserving his own life until the end of the war. The fact that Yossarian relives Snowden's death on multiple occasions throughout the novel shows how close Death remains to his thoughts. He considers the number of ways that death can happen and finds his way into the squadron hospital as soon as possible.
Rather than depressing him (at least for the most part), the certainty of death makes Yossarian try to seize as much as he can from each day. His love affairs are passionate (if brief), and he keeps looking for opportunities to enjoy himself.
Religion vs. Belief
One of the more controversial themes from Catch-22 has to do with the contradictions between outward signs of piety and genuine belief in God. Colonel Cathcart wants to make his own squadron look good by copying ideas that got other units into magazines. He wants prayers before missions, as long as they don't involve God too much. He wants the chaplain to send home personalized letters of condolence to each fallen airman, but he is happy with the form letter that the chaplain's assistant puts together, because it basically takes care of the purpose without making too much work for him. The chaplain's assistant, in a further twist of irony, happens to be an atheist. He just enjoys the fact that his role brings him visibility within the squadron and insulates him from having to do more combat missions.
Yossarian has a discussion about religion with Scheisskopf's wife during one of their sexual romps. Neither of them believe in God, but they both have a concept about what they think God is like. They frame it in an interesting way: Yossarian does not believe in a feckless, ineffective deity, while Mrs. Scheisskopf does not believe in a God who is just and loving. What is interesting here is that both of them have contexts that have built in them an idea of what God is like, even though they claim not to believe in His existence.
So does this mean that both Yossarian and Mrs. Scheisskopf are true atheists? Or are they merely disappointed in the God that they expected to act differently with regard to the world?
Yossarian takes God's lack of involvement in the world as license to come to his own conclusions about right and wrong and live by those conclusions. When he changes his purpose to self-preservation, that is one such decision. At the end, when he refuses to sell out the rest of the men in the squadron and tries to escape rather than take the deal from Colonel Cathcart and Colonel Korn, which would send him home with honor instead of having to fly more missions, that is another. In his own way, Yossarian has chosen to go out a hero.