Must I do what I ought (or will the least I can do do)?

Appears to give the first model-theoretic account of both "must" and "ought" (without conflating them with one another). Some key pre-theoretic semantic and pragmatic phenomena that support a negative answer to the main title question are identified and a conclusion of some significance is drawn: a pervasive bipartisan presupposition of twentieth century ethical theory and deontic logic is false. Next, an intuitive model-theoretic framework for "must" and "ought" is hypothesized. It is then shown how this hypothesis helps to explain and predict all the pre-theoretic phenomena previously observed. Next, I show that the framework hypothesized possesses additional expressive and explanatory power (e.g. derivatively predicting the existence of supererogatory and permissibly suboptimal alternatives), thus adding further confirmation that it is on the right track.