This dissertation examines whether Thomas Scanlon’s contractualism satisfactorily explains its intended domain of morality which he terms “what we owe to each other.” Scanlon proposes that such interpersonal morality is based on justifying one’s actions to others by behaving according to principles that could not be reasonably rejected. This idea accounts for two key functions of a moral theory: explaining how moral judgments are made and why agents generally act according to these judgments. After reviewing the nature of constructivist moral theories to show why I chose to focus on Scanlon’s theory, I assess how effectively it fulfills these two roles. I argue that the concept of justifiability is necessary for making moral judgments becau...