All animals, all material objects, are caught up in events that seem to have a temporal location, a temporal order and a temporal duration. Outside human life, however, this is implicit rather than explicit. We alone table time and clock it. What is it about us that enables us to do this? I want to argue that our sense of time as something in itself is due, at least in part, to the strange, even paradoxical, character of vision. It is this, I believe, that has set us on a path in which our scientific understanding and our lived experience of time have diverged, something of which I complained in the previous essay.

Our gaze sees not only what is visible, but also that there are things or parts of things that are in visible. An object that hid nothing, either its own interior or other objects behind it, because it was absolutely transparent would be invisible. The visual field is dappled with visible invisibility. It even has visibly invisible limits: the curtained window, the bend in the road, the outline of the hill, all visually display that which is not, but might be, seen. There is nothing comparable to this in the other senses. For example, although we sometimes talk of an audible, even a loud or deafening, silence, this is not meant literally. We do not hear the inaudible as we see the invisible.