Trying to capture the essence of a concept like energy is like being in a maze and having a great deal of difficulty finding the exit. There is always an exit out of the maze, albeit perhaps well hidden. Disguised beneath the facade of a particulate, mechanistic universe in which energy is transferred, used, lost or gained when one thing acts on another, there has been, throughout history, a subtle idea that energy is more than just the ability to do work. Energy is a phenomenon.