The very concept of a mind would appear to have little purpose if the mind were able to neither to have some influence on the physical body nor to be influenced by it. Moreover, if the mind is merely an ´epiphenomenon´ - some specific, but passive, feature of the physical state of the brain - which is a byproduct of the body but which can have no influence back upon it, then this might seem to allow the mind just an impotent frustrated role. But if the mind were able to influence the body in ways that cause its body to act outside the constraints of the laws of physics, then this would disturb the accuracy of those purely physical scientific laws. It is thus difficult to entertain the entirely ´dualistic´ view that the mind and the body obey totally independent kinds of law. Even if those physical laws that govern the action of the body allow for a freedom within which the mind may consistently affect its behaviour, then the particular nature of this freedom must itself be an important ingredient of those very physical laws.

Roger Penrose