For "choice under uncertainty" the twin assumptions of rationality and market efficiency, as more closely defined, lead to modern portfolio theory (MPT) with its capital asset pricing model (CAPM)—an equilibrium-based result—and to the Black–Scholes–Merton theory (BSM; often, simply Black–Scholes) for option pricing—an arbitrage-free result. Note that the latter derivative prices are calculated such that they are arbitrage-free with respect to the more fundamental, equilibrium determined, securities prices; see asset pricing.