Adam Smith, in Wealth of Nations, used gravitation as a rhetorical metaphor and not in a formal philosophical sense, as used by Newton, Aristotle or Empedocles. Physical gravitational attraction is predictable, accurate and rule-bound; metaphoric gravity, as in relationships between natural and market prices, are neither strictly rule-based nor predictable. Market exchange relationships between independent people are subject to the vagaries of imperfect rhetorical persuasion....