Themes are the fundamental and often universal ideas explored in a literary work.
Whether we read Slaughterhouse-Five as a science-fiction novel or a quasi-autobiographical moral statement, we cannot ignore the destructive properties of war, since the catastrophic firebombing of the German town of Dresden during World War II situates all of the other seemingly random events. From his swimming lessons at the YMCA to his speeches at the Lions Club to his captivity in Tralfamadore, Billy Pilgrim shifts in and out of the meat locker in Dresden, where he very narrowly survives asphyxiation and incineration in a city where fire is raining from the sky.
However, the not-so-subtle destructiveness of the war is evoked in subtle ways. For instance, Billy is quite successful in his postwar exploits from a materialistic point of view: he is president of the Lions Club, works as a prosperous optometrist, lives in a thoroughly comfortable modern home, and has fathered two children. While Billy seems to have led a productive postwar life, these seeming markers of success speak only to its surface. He gets his job not because of any particular prowess but as a result of his father-in-law’s efforts. More important, at one point in the novel, Billy walks in on his son and realizes that they are unfamiliar with each other. Beneath the splendor of his success lies a man too war-torn to understand it. In fact, Billy’s name, a diminutive form of William, indicates that he is more an immature boy than a man.
Vonnegut, then, injects the science-fiction thread, including the Tralfamadorians, to indicate how greatly the war has disrupted Billy’s existence. It seems that Billy may be hallucinating about his experiences with the Tralfamadorians as a way to escape a world destroyed by war—a world that he cannot understand. Furthermore, the Tralfamadorian theory of the fourth dimension seems too convenient a device to be more than just a way for Billy to rationalize all the death with he has seen face-to-face. Billy, then, is a traumatized man who cannot come to terms with the destructiveness of war without invoking a far-fetched and impossible theory to which he can shape the world.
In Slaughterhouse-Five, Vonnegut utilizes the Tralfamadorians, with their absurdly humorous toilet-plunger shape, to discuss the philosophical question of whether free will exists. These aliens live with the knowledge of the fourth dimension, which, they say, contains all moments of time occurring and reoccurring endlessly and simultaneously. Because they believe that all moments of time have already happened (since all moments repeat themselves endlessly), they possess an attitude of acceptance about their fates, figuring that they are powerless to change them. Only on Earth, according to the Tralfamadorians, is there talk of free will, since humans, they claim, mistakenly think of time as a linear progression.
Throughout his life, Billy runs up against forces that counter his free will. When Billy is a child, his father lets him sink into the deep end of a pool in order to teach him how to swim. Much to his father’s dismay, however, Billy prefers the bottom of the pool, but, against his free will to stay there, he is rescued. Later, Billy is drafted into the war against his will. Even as a soldier, Billy is a joke, lacking training, supplies, and proper clothing. He bobs along like a puppet in Luxembourg, his civilian shoes flapping on his feet, and marches through the streets of Dresden draped in the remains of the scenery from a production of Cinderella.
Even while Vonnegut admits the inevitability of death, with or without war, he also tells us that he has instructed his sons not to participate in massacres or in the manufacture of machinery used to carry them out. But acting as if free will exists does not mean that it actually does. As Billy learns to accept the Tralfamadorian teachings, we see how his actions indicate the futility of free will. Even if Billy were to train hard, wear the proper uniform, and be a good soldier, he might still die like the others in Dresden who are much better soldiers than he. That he survives the incident as an improperly trained joke of a soldier is a testament to the deterministic forces that render free will and human effort an illusion.