If the physical world is causally closed, then there is a physical reason we talk about something called "consciousness." Any claims we might make that it can't be physically explained become somewhat outlandish, since the reason we make these claims can be. But even if the physical isn't closed, we still identify consciousness with intrinsic properties that aren't defined solely by their causal roles. For example, the color yellow is more than just "that which causes us to judge things yellow." There is something it is like to be experiencing the color yellow. The problem is that anything we can say about yellow, or a yellow experience, or consciousness in general, must have been caused by something, be it physical or non-physical. If there are intrinsic (ie, non-extrinsic, or non-causal) properties, how could we ever talk about them, or even know about them? The problem is more tractable if it's broken up into two parts. First, does the specific nature of an experience have an effect. That is, if someone saw green as what I call red, could they still conceivably behave the same as me? The answer to this seems to be yes, and is evidence that there can be properties that do not cause and yet we can still know about (ie, I know what green looks like to me). There is nothing my inverted spectrum twin could say that would cause me to realize we see the color differently, and hence there is no infringement on the causal closure of the physical world. And yet, there is still a natural difference between me and him. The more difficult question is "Can the existence or absence of experience have an effect?" The trouble is, while we can't convey the specific nature of an experience, which meshes well with that nature not being able to cause, we can tell people that we have experiences. How can it be that intrinsic properties cause us to talk about their existence? What causes us to believe in things that can't cause?