Memory is a strange thing. Suddenly, for no apparent reason, it will pop up an image of you standing in a doorway, aged seven, and then a minute later refuse to tell you your PIN. Memory is a shape-shifter, interpreting and re-interpreting, sometimes explaining you to yourself, sometimes excusing, sometimes deceiving. We all have shared memories too—but surprisingly often they turn out to be not quite as shared as we might expect, for we remember similar experiences in strangely different ways. And then there are the cultural memories by which groups and communities and societies remember their recent past. Postmodernists…