Many philosophers presume that an adequate moral theory can in principle determine what is morally right and wrong given all the relevant empirical facts. Many such philosophers believe that modern moral theories, such as Kantian and consequentialist theories, can meet this determinacy criterion while Aristotelian moral theory cannot. This charge of indeterminacy has become a standard objection to Aristotelian moral theory. In this dissertation, however, I argue that meeting this determinacy criterion is not necessary for a moral theory to be adequate. I argue that Kantian and consequentialist moral theories are more indeterminate than philosophers often presume. I also argue that Aristotelian moral theory is not as indeterminate as many philosophers believe. This dissertation is a call to modesty in response to philosophers inflating the power of modern moral theory to determine right and wrong. Indeterminacy, I also argue, is also not necessarily a bad feature for Kantian, consequentialist, or Aristotelian moral theory. All three types of moral theory are what I call "teleological ideal theories" that require phronesis (good practical and normative judgment) for an agent (or philosopher) to determine right — be it in terms of Kantian respect for persons, consequentialist maximizing, or Aristotelian virtue.