In a work of literature, a theme is a recurring, unifying subject or idea, a motif that helps us better understand a work of art. With a novel as richly ambiguous as Catch-22, we look to themes as guides; but it is important to be open-minded and flexible while we do so. A good deal is left to individual interpretation so that one reader might disagree with another without necessarily being "wrong" or "right" about what the novel is saying. Heller employs themes in the manner of a musical composer, often introducing them briefly, then returning as the novel progresses, embellishing and augmenting as he goes. Some of the major themes involve the concept of Catch-22, the distortion of justice, the influence of greed, and the issue of personal integrity.
The code under which the airmen of the 256th Squadron exist is embodied in the theme of Catch-22. As a general rule covering most behavior, it establishes that the men who fight the war are going to have to do what those in authority tell them; and there is no way out of that. Doc Daneeka explains the concept to Yossarian in Chapter 5 when Yossarian asks if his tent mate, Orr, can be grounded. Anyone who is crazy can be grounded. Doc says that Orr certainly could be grounded, but first he would have to make a request. Orr doesn't make that request because he's crazy — he'd have to be crazy to keep flying missions. But if he asked to be grounded, that would mean he is sane. Anyone who wants out of combat duty isn't really crazy and thus cannot get out:
There was only one catch and that was Catch-22, which specified that a concern for one's own safety in the face of dangers that were real and immediate was the process of a rational mind. Orr was crazy and could be grounded. All he had to do was ask; and as soon as he did, he would no longer be crazy and would have to fly more missions. Orr would be crazy to fly more missions and sane if he didn't, but if he was sane he had to fly them. If he flew them he was crazy and didn't have to; but if he didn't want to he was sane and had to.
