Checking Groups and Gaps

A housing association’s repairs report lists “heating repairs” beside “high-rise repairs”. A broken boiler on the ninth floor belongs to both. Add the two counts together and that repair is counted twice, and the report claims more work than was done.

Think of the pigeonholes in a sorting office. Every letter goes in exactly one hole, and there’s a hole marked “other”, so nothing is left on the floor. MECE, short for mutually exclusive, collectively exhaustive, is the same check for the groups under an argument: do they overlap, and do they cover everything they claim to? It checks the sorting, not whether what’s sorted is true.