The intellectual journey on which I am about to embark, although not an unusual one in philosophy, may at first seem strange to those who are in the habit of looking to science for the answers to their big questions, including their philosophical questions. For I propose to shed light on the problematic relationship between two things, namely, mental illness and physical illness, by comparing their relationship to the relationship between two other things, namely, a rhyme for the eye—which will be explained shortly for the benefit of anyone unfamiliar with this concept—and a rhyme for the ear. Yet these two pairs of things are not related in any way by subject-matter. In philosophy, however, this sort of deliberate dislocation can be beneficial. As Wittgenstein himself once remarked, ‘A philosophical] problem can be solved only in the right surrounding, we must give the problem a new surrounding, we must compare it to cases we are not used to compare [sic] it with.’

To someone who is used to treating only scientific enquiries as serious enquiries my extended comparison between two such entirely different pairs of concepts may sound misguided, even frivolous. But a conceptual investigation is a very different sort of thing from a scientific investigation and I shall take heart from the words of a short untitled poem by Emily Dickinson which remind us of the existence of a kind of truth which is so disconcerting to its intended audience that, if it is eventually ever to do them any good, it needs to be presented to them gradually.