The theory of choice receives formal treatment in decision theory, game theory and substantial parts of economics. However there is cause for concern that the formal treatment of the subject has advanced beyond the substantive grounds on which it relies. For, the formal theories fundamentally rely on a concept of preference, which is itself lacking a viable substantive interpretation. Indeed the challenges to the substantive interpretation of ‘preference’ threaten to undermine the standard arguments used to justify the completeness and transitivity conditions on which Preference Theories rely. This discussion will explore whether a conception of rationality, anchored in a larger conception of practical reasoning, can justify the completeness and transitivity conditions. Specifically, this dissertation will draw on recent developments in philosophy of law, action theory and ethics to enumerate a conception of practical reasoning that takes reasons to be the basic normative concept. It will then seek to offer an account of rationality that is distinct from, but complementary to, the role of reasons. And from this foundation develop an account of preferences that includes many of the characteristics of standard accounts, yet is situated within this broader context. From this vantage point, the discussion will explore possible justifications for the completeness and transitivity conditions. Ultimately, it will be argued that both can be justified – though with different force – in specified domains. While the discussion will primarily focus on the justification of the completeness and transitivity conditions, it is in part motivated by the goal of exploring the connections between the treatment of choice in the distinct fields associated with Preference Theories and action theory broadly defined. In so doing, the hope is to suggest that there is promise in drawing together formal and substantive treatments of choice which is deserving of greater attention.