WHEN I WAS A boy, after my mother died, I always tried hard to hold her in my mind as I was falling asleep so maybe I'd dream of her, only I never did. Or, rather, I dreamed of her constantly, only as absence, not presence: a breeze blowing through a just-vacated house, her handwriting on a notepad, the smell of her perfume, streets in strange lost towns where I knew she'd been walking only a moment before but had just vanished, a shadow moving away against a sunstruck wall.