One essay claims that theories of this concept must apply to beings whose minds are made of hydraulic pumps and men who cross their legs and snap when exercising on an empty stomach. Ninian Smart criticized a theory that prioritizes this concept with the example of a (*) "benevolent world-exploder." The absence of this concept is good but the absence of its opposite is not necessarily bad, according to David Benatar’s asymmetry argument. Public policy should prioritize this concept according to a “negative” theory developed by Karl Popper. David Lewis defended a theory of mind he developed with D. M. Armstrong in a paper on the ■END■