# Universality criterion

The Universality criterion requires that a system give unique results for a given set of ranked ballots. It was stated by Kenneth Arrow as part of his impossibility theorem, and it is such a basic criterion that it's satisfied by all non-random ranked systems. However, since it was defined by Kenneth Arrow before there had been theoretical analysis of rated voting systems, it does not apply to rated ballots, and so all rated systems technically violate universality. This is why some rated systems, such as MCA-P, can appear to violate Arrow's theorem by satisfying all of his more-interesting criteria such as monotonicity and independence of irrelevant alternatives. When not combined with (ranked) universality, those other criteria are not incompatible.