Different moralities must share some general features if they are to perform their functions of coordinating beings having particular kinds of motivations. Morality is a cultural construction in something like the way bridges are. There would be no bridges unless human beings used them to move across bodies of waters or depressions in the earth, but a good bridge cannot be designed according to whim, but rather according to what would adequately fulfill their function and the nature of the materials that are available for their construction.