Anna Mahtani (LSE) gives a talk at the MCMP Colloquium (16 December, 2015) titled "How (not) to make everyone better off". Abstract: he concept of ‘pareto superiority’ plays a central role in welfare economics. Pareto superiority is sometimes taken as a relation between outcomes, and sometimes as a relation between actions – even where the outcome of the actions is uncertain. Whether one action is classed as (ex ante) pareto superior to another depends on the prospects under the actions for each person concerned. I argue that a person's prospects (in this context) can depend on how that person is designated. Without any constraints on acceptable designators, then, the concept of pareto superiority is incomplete and gives inconsistent results. I consider various ways of completing the concept, and draw out the implications for debates in welfare economics.