Could the brain be working without consciousness? Does the brain interact with consciousness? Alternately, is it that consciousness can't really control the brain, and you only have the impression that you make the decisions, but your brain does.
If the answer to the last question is yes, it is impossible to know if someone else has a consciousness? Even if he doesn't, he'll say he does, because the brain thinks he does.
We can't be made only from matter. If we would, we'd be a mix of chemicals interacting with each other. What makes us be aware of our feelings, what we think, and our 5 senses?
When and how is consciousnesses created?