While I was working on Lincoln’s Dreams , any number of people asked me why I was writing a book about the Civil War, but no one at all asked me why I was writing a book about dreams. Instead, when I told them what the book was about, they began telling me about dreams they had had, as if I could tell them what they meant.

I had no idea. I have no idea what any dreams mean. All the latest research seems to indicate that they don’t mean anything—that they are nothing more than the nervous system’s charwoman, tidying up after the day’s events, taking out the trash. And that makes very good sense. (Why else would we dream about empty creamer packets that steal a parakeet?) But something in us rebels at the idea that they’re the day’s detritus, because dreams so obviously mean something.

Freud thought so, too. He wrote his dreams down in painstaking detail (they are as ridiculous as ours—full of flower monographs and false teeth) and pored over them, trying to decipher their meaning. He decided they were dispatches from our unconscious: longing sighs and murmured memories and cries for help, all sent in a complicated code.

And that seems logical, too, until it comes to the deciphering. (“The creamer packets clearly represent your yearning for your mother’s breast …”) Because it’s not a code, it’s another language. And their images can’t be reduced to symbols. Dreams are something more, something else.