Aggregation and the relevance of some issues for others

A general collective decision problem is analysed. It consists in many issues that are interconnected in two ways: by mutual constraints and by connections of relevance. The goal is to decide on the issues by respecting the mutual constraints and by aggregating in accordance with an informational constraint given by the relevance connections. Whether this is possible in a non-degenerate way depends on both types of connections and their interplay. One result, if applied to the preference aggregation problem and adopting Arrow''s notion of (ir)relevance, gives Arrow''s Theorem, without excluding indifferences unlike in the existing general aggregation literature.