Time and memory
The science fiction elements of the novel include time travel. Billy leaps in time, experience his life's events out of order and repeatedly. He learns on the alien world of Trafalmadore that all time happens simultaneously; thus, no one really dies. But this permanence has its dark side: brutal acts also live on forever. Memory is one of the novel's important themes; because of their memories, Vonnegut and Billy cannot move past the Dresden massacre. Billy leaps back in time to Dresden again and again, but at critical points we see Dresden simply because Billy relives it in his memory.
Narrative versus non-narrative and anti-narrative
This is a broad theme that encompasses many important ideas. Vonnegut is interested in protecting his novel from becoming a conventional war narrative, the kind of conventional narrative that makes war look like something exciting or fun. Throughout the book, we see narratives of this kind in history texts and the minds of characters. But this novel is more interested in non-narrative, like the nonsense question asked by birds at the novel's end, or anti-narrative, like the out-of-order leaping through the many parts of Billy's life. Vonnegut does not write about heroes. Billy Pilgrim is more like a victim.
The relationship between people and the forces that act on them
This theme is closely connected to the idea of narrative. Vonnegut's characters have almost no agency. They are driven by forces that are simply too huge for any one man to make much of a difference. Vonnegut drives home this point by introducing us to the Trafalmadorians and their concept of time, in which all events are fated and impossible to change.
Acceptance
One of the book's most famous lines is "So it goes," repeated whenever a character dies. Billy Pilgrim is deeply passive, accepting everything that befalls him. It makes him able to forgive anyone for anything, and he never seems to become angry. But this acceptance has it problems. When Billy drives through a black ghetto and ignores the suffering he sees there, we see the problem with complete acceptance. Vonnegut values the forgiveness and peace that come with acceptance, but his novel could not be an "anti-war book" if it called on readers to completely accept their world.
Human dignity
In Vonnegut's view, war is not heroic or glamorous. It is messy, often disgusting, and it robs men of their dignity. The problem of dignity comes up again and again in the novel, as we see how easily human dignity can be denied by others. But Vonnegut also questions some conceptions of dignity; he sees that they have a place in creating conventional war narratives that make war look heroic.
