Well, now I understand why you Salty (and many others) are strict materialists, I was wondering how you could reconcile the differences between matter and energy? Ahh, there is no essential difference. Perhaps all that you are saying is that they are interchangeable phenomena, thus not exclusively separate entities. But I think humans DO manage to perceive the difference Matter is substance that occupies space and has weight, and can exist as a solid, a liquid, or a gas; Energy is a capacity to do work. Light, heat, and electricity are forms of energy. Of course one can turn into the other and vice versa, energy is after all either kinetic or potential.