  A classification is a surjective mapping from a set of objects to a set of
categories. A classification aggregation function aggregates every vector of
classifications into a single one. We show that every citizen sovereign and
independent classification aggregation function is essentially a dictatorship.
This impossibility implies an earlier result of Maniquet and Mongin (2016), who
show that every unanimous and independent classification aggregation function
is a dictatorship. The relationship between the two impossibilities is
reminiscent to the relationship between Wilson's and Arrow's impossibilities in
preference aggregation. Moreover, while the Maniquet-Mongin impossibility rests
on the existence of at least three categories, we propose an alternative proof
technique that covers the case of two categories, except when the number of
objects is also two. We also identify all independent and unanimous
classification aggregation functions for the case of two categories and two
objects.
