Insanity—in clinical practice as in the popular imagination—is seen as a state of believing things that are not true and perceiving things that do not exist. Most schizophrenics, however, do not act as if they mistake their delusions for reality. In a work of uncommon insight and empathy, Louis A. Sass shatters conventional thinking about insanity by juxtaposing the narratives of delusional schizophrenics with the philosophical writings of Ludwig Wittgenstein.