This paper shows how the debate on information in Welfare Economics is enriched from the perspective of Lisa Herzog's thesis on citizen knowledge, and conversely. First, the two sources of information for welfare enhancing public decisions, individual utilities and knowledge, need articulated justification, insofar as knowledge may be used to revise individual utilities. The process of preference revisions implicitly assumes the coincidence between knowledge and truth, but there are compelling arguments why this assumption should be debated. Second, public decisions are ultimately based on an additional third component of information: collective ethical norms. They are decisive, but their legitimacy is conditional to their transparency in the debate between experts and citizens. Transparency on which knowledge is judged relevant hence constitutes a minimal condition for the design of democratic infrastructures involving public decision making.