"For example, Christian writer and medievalist C. S. Lewis made the argument in his popular book "Mere Christianity" that if a supernatural, objective standard of right and wrong does not exist outside of the natural world, then right and wrong becomes mired in the is-ought problem.Thus, he wrote, preferences for one moral standard over another become as inherently indefensible and arbitrary as preferring a certain flavor of food over another or choosing to drive on a certain side of a road.