We have made huge progress in understanding the biology of mental illnesses, but comparatively little in interpreting them at the psychological level. The eminent philosopher Jonathan Glover believes that there is real hope of progress in the human interpretation of disordered minds.

The challenge is that the inner worlds of people with psychiatric disorders can seem strange, like alien landscapes, and this strangeness can deter attempts at understanding. Do people with disorders share enough psychology with other people to make interpretation possible? To explore this question,...