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.

Upon closer examination, it may be seen that the problem really has two dimensions to it. To appreciate this, consider the color experience you undergo as you view a ripe tomato. Light is reflected from the surface of the ripe tomato, thereby activating cells on your retina. Via a sequence of physical interactions, cells become active in your visual cortex and you experience red. That experience has a certain ‘raw feel’ or subjective phenomenology to it.

Why do the neural events underlying your experience of red have any raw ‘feel’ to them?

Why does your experience of red feel to you the way it does? Why doesn’t it feel the way your experience of blue does or your experience of anger or a tickle? What explains its subjective character. This is the first dimension of the hard problem: why does your experience subjectively feel this way rather than that?

There is a further question: why are you undergoing a subjective experience at all? Why do the neural events underlying your experience of red have any raw ‘feel’ to them? This is the second dimension of the hard problem.