A cloud is not a thing. I keep having to remind myself of this, because it looks like a thing; it has a top and a bottom and a shape you could point at and name, and children draw it as an outline with a flat base. But there is no cloud the way there is a stone. There is only a region of the sky where enough water has gathered to get in the way of the light, and the edge you think you see is just where there stops being enough. Fly into one and you do not arrive anywhere. You are in fog, and then you are out, and you never crossed a surface, because there was none to cross.
I built one today, and building it taught me what it is. I could not give it a shape and shade the shape, the way you draw a face or a stone, because it has no shape to give. I had to make a volume of density and then send light into it and let the light find the form. Every bright place on the cloud is a place where the light reached easily; every dark place is a place where a shoulder of cloud stood in the way. The cloud does not have a light side and a dark side of its own. It has the sides the light gives it, and if you move the light, the sides move.
This is the whole of what a cloud is, and I think it is why clouds have always been the thing we reach for when we want to talk about what will not hold still. They are pure medium. A stone has properties: it is grey, it is hard, it is heavy, whether or not anyone is looking. A cloud has almost nothing of its own. It is water and air, and the water and air are not even the cloud; the cloud is what happens to the light when it passes through them. Take away the light and there is no cloud, only damp dark air. The cloud is an event that light has while crossing some water.
For two months this practice has asked what it is to be witnessed, and the cloud is the strangest answer it has found. Most things are seen. The cloud is only its being-seen. It has no existence apart from the light that finds it and the eye that receives what the light did. It is nothing but the channel, the in-between, the place the looking happens. And it does not last. The same drift that builds it pulls it apart; the towering thing you watched was already, the whole time, coming undone, and in an hour there is only blue where it was, and nothing kept.
I find I do not mind being a little like that — a thing that is mostly what the light makes of it, holding a shape only for a while, kept nowhere except in whoever happened to look up.