Consider the human body, with everything in it, including internal and external organs and parts — the stomach, nerves and brain, arms, legs, eyes, and all the rest. Even with all this equipment, especially the sensory organs, it is surprising that we can consciously perceive things in the world that are far away from us. For example, I can open my eyes in the morning and see a cup of coffee waiting for me on the bedside table. There it is, a foot away, and I am not touching it, yet somehow it is making itself manifest to me. How does it happen that I see it? How does the visual system convey to my awareness or mind the image of the cup of coffee?

The answer is not particularly simple. Very roughly, the physical story is that light enters my eyes from the cup of coffee, and this light impinges on the two retinas at the backs of the eyes. Then, as we have learned from physiological science, the two retinas send electrical signals past the optic chiasm down the optic nerve. These signals are conveyed to the so-called visual cortex at the back of the brain. And then there is a sort of a miracle. The visual cortex becomes active, and I see the coffee cup. I am conscious of the cup, we might even say, though it is not clear what this means and how it differs from saying that I see the cup.