" Finance is concerned with the relations between the values of securities and their risk, and with the behavior of those values. It aspires to be a practical, like physics or chemistry or electrical engineering. As John Maynard Keynes once remarked about economics, “If economists could manage to get themselves thought of as humble, competent people on a level with dentists, that would be splendid.” Dentists rely on science, engineering, empirical knowledge, and heuristics, and there are no theorems in dentistry. Similarly, one would hope that nance would be concerned with laws rather than theorems, with behavior rather than assumptions. One doesn’t seriously describe the behavior of a market with theorems. "

― Emanuel Derman , The Volatility Smile (Wiley Finance)