Consider: 1. Energy is a system's ability to do work. 2. Work is force over a distance. 3. A force is applied over some distance. 4. All physical change (i.e. all change in a system through its phase space) is the result of force. ∴ Therefore, energy would seem to be a system's ability to change. (Here I mean "change" both transitiviely and intransivitiely, both "to change" as in to be changed and "to change" as in to effect change.) But that sounds too cute and nice. Or maybe it's just so general that no one would need it. Any guidance here? Is this reasoning actually flawed? If so, could some more accurate restatement reach the same conclusion? I'm trying to get a sort of root intuitive understanding here, something I've always lacked on the nature of energy.