We are conscious. Rocks and trees are not. Why? The obvious answer is that we have brains and they do not. But all sorts of physical events occur in our brains that have nothing to do with consciousness.

Think of the neurophysiological mechanisms responsible for our continuing to breath or our hearts beating. What is it about the neurological goings-on underlying our conscious states that explains why they generate the conscious states they do or why they generate anything conscious at all for that matter? This is the hard problem of consciousness.