The model is provided for us by these things in front of us which at first glance seem entirely determinate: this stone is white, hard and cool, and it seems that the world is crystallized in it, that it has no need of time in order to exist, that it wholly unfolds itself in the instant, and that any additional existence would involve it in a fresh coming into being, so that we are tempted to think that the world, if it is anything at all, can be only a collection of things analogous to this stone, and time a collection of perfect instants.