When we talk about ghosts, we are speaking in layers of metaphor. We are not usually speaking about wispy bodies in rotting shrouds, but about family secrets, buried impulses, unsolved mysteries, anything that lingers and clings. We are speaking of the sense of loss that sometimes overtakes us, a nostalgia for something that we can't name. There is a way in which the question "Do you believe in ghosts?" is unnecessary to ask: we all know a few, and they walk at all hours, if only through our memories. Our ancestors are encoded in our genes. Look at your face in the mirror, and one day you will see one of your parents, moving under your own skin; the next day it may be a grandparent who has come to visit. Within you, there are people you have never been able to mourn because you never knew them, people from the distant past; the traces of your animal ancestors still live in your instincts, in your physiology. As products of evolution, we carry all the past inside us; we are walking repositories of the lost.
I have written a memoir called Giving Up the Ghost, which is about my own childhood, but also about my ancestors and children who were never born, and about the ghosts we all have in our lives: the ghosts of possibility, the paths we didn't take, and the choices we didn't make, and expectations, which seemed perfectly valid at the time, but which somehow or other weren't fulfilled. I describe ghosts like this: "They are the rags and tags of everyday life, information you acquire that you don't know what to do with, knowledge that you can't process; they're cards thrown out of your card index, blots on the page."