  The allegedly meaningless scenario is a case of interpersonal (or intersubjective) spectrum inversion: Invert is spectrally inverted with respect to another person, Nonvert. But there is another sort of inversion scenario, in which a single person’s qualia are inverted with respect to her qualia at an earlier time. As Shoemaker notes (1982, 327), a case of intrapersonal (or intrasubjective) spectrum inversion appears to have been first discussed by Wittgenstein: