Imagine a strange and common experience—you reach for something concrete, immediately in front of you—only to find that the solid has evaporated. Accelerate towards a pool of water on the road, outline a column of light, cup your hand around smoke or fog. The reflection waits on the pavement before you, the column stands endlessly beside you. When you open your hand, it is empty. Only a residue, carbonate or cool, attests to the reality that was smoke or cloud.

Thus we create a curious category of realities undeniable but impossible to grasp. Older now, but still determined, we continue to fill the category: it grows more sophisticated, stranger and more various with our experience. It is fed each time we try to capture, this time in words or memory, a scent, a face, a motion that defies definition. It is fed by all the realities language cannot describe and by all that is known in the way of an old routine, with familiar and fading certainty. It is fed by everything eminently sensible and constantly elusive. Power perhaps.