Vonnegut's novels are science fiction, will he or nil he. Listen, Slapstick is about a pair of telepathic twins whose intelligences synergize into super-genius when they're in close proximity but deteriorate to bright-normal when they're farther apart. They pretend to be idiots, however, as a form of protective coloration. Nice old science fiction device, first used by Olaf Stapledon around 1935, I believe. It also involves a scheme to relieve population pressures by breeding miniature humans—Bob Bloch did this in the 1960s. And there's a future plague which reduces most of the world to a state of neo-barbarism-in-the-ruins. Cf. Jack London, 1915. (pp. 52-3)

[Slapstick is] a science fiction novel if ever there was one….

As for whether Slapstick is a good science fiction novel or not, that's another matter. It has all of the trademarks of Vonnegut's novels, since the first few: a bitter zaniness, a deceptively simple...