This thesis concerns the nature of the concept of feasibility and its role in constraining moral and political philosophy: to what extent and in what way facts about feasibility ought to constrain what moral and political theory say. I begin in my first chapter by giving an account of feasibility, that is, by attempting to understand what we mean when we say that some outcome is or isn’t feasible. I argue against the various attempts that have been made in the literature to give a binary definition (e.g. Gilabert and Lawford-Smith, Räikkä). There is a multiplicity of different possible sharpenings of the term ‘feasible’, no single one of which is obviously privileged. Different sharpenings hold fixed different ranges of facts, making different sets of proposals feasible. In the remainder of the thesis, I go on to relate this account of feasibility to moral and political theory. I argue that it is not clear which sharpenings of ‘feasibility’ constrain which sorts of moral theory. I engage with the literature on ‘ideal theory’, arguing that theory constrained only by expansive (permissive) sharpenings of ‘feasibility’ (which is one thing that could be meant by ‘ideal theory’) is useful and important for the purpose of practical action guidance. I thus draw two important conclusions. The first is the thesis of the first chapter about the concept of feasibility. I then build on this to get to a more substantive methodological conclusion, that theory constrained only by permissive (unrealistic) feasibility constraints is useful
