Can an axiomatic justification be given for the requirement that society picks all and only Pareto optimal alternatives at each profile of individual preferences? Using the framework of fixed-agenda social choice theory, we present a characterization of the Pareto optimal social choice correspondence. We introduce a new independence condition, P-independence. When combined with three natural assumptions, P-independence leads to the conclusion that the social choice set and the Pareto optimal set are the same. (C) 2020 Elsevier B.V. All rights reserved.