Computers have become an extension of us: that is a commonplace now. But in an important way we may be becoming an extension of them, in turn. Computers are digital — that is, they turn everything into numbers; that is their way of seeing. And in the computer age we may be living through the digitization of our minds, even when they are offline: a slow-burning quantification of human affairs that promises or threatens, depending on your outlook, to crowd out other categories of the imagination, other ways of perceiving.