‘Do you hear voices?’ It’s not always wise to answer in the affirmative. In a famous experiment in 1973, the Stanford psychologist David Rosenhan and seven other perfectly sane people requested admission to mental hospitals, claiming that they were hearing an inner voice saying ‘empty’, ‘hollow’ or ‘thud’. Seven of the eight participants were admitted, diagnosed with schizophrenia and released only after accepting the label.

In fact the great majority of us hear voices in our heads – when we read or write, when our mind wanders, as we drift off to sleep. As children we learn to speak by vocalising them, and inner monologues and dialogues become an essential part of thinking. As we discover when learning to meditate, it’s remarkably difficult to shut them up. 

When Charles Fernyhough began studying inner voices twenty years ago, the field was relatively untilled. There was no clear methodology: such irreducibly subjective phenomena are impossible to verify, and even the best descriptions distort the original experience. In the interim he has dedicated himself to mapping the contours of his