  We adopt in this work the idea that the building blocks of the visible
Universe belong to a class of the irreducible representations of the Poincare
group of transformations (the "things") endowed with classificatory quantum
numbers ("the properties"). After a discussion of this fundamentality, the
question of the nature of both "dark" components of the Universe which are
deemed necessary, but have not been observed, is analyzed within this context.
We broadly discuss the ontology of dark matter/dark energy in relation to the
irreducible representations of the Poincar\'e group + quantum numbers, pointing
out some cases in which the candidates can be associated to them, and others
for which a reclassification of both the dark and visible (ordinary) components
would be needed.
