Consciousness is experience considered as a kind of substance, considered, that by itself. As such it is subject to many kinds of strange internal relations, like causality but so much more general. The category of causality is an abstraction from the inwardly known co-arisals of consciousness. And it is closed in that the only things that can affect consciousness are consciousness, and necessarily the 'same' consciousness, although sameness and difference have a different a different and more original sense too. Consider, for example, how the other's consciousness appears to affect your own, how for this to happen there must be a common substrate beyond any theories of mind.