  We discuss two categorical characterizations of the class of acyclic maps
between (path-connected) spaces. The first one is in terms of the higher
categorical notion of an epimorphism. The second one employs the notion of a
balanced map, that is, a map whose homotopy pullbacks define also homotopy
pushouts. We also identify the modality in the homotopy theory of spaces that
is defined by the class of acyclic maps, and discuss the content of the
generalized Blakers-Massey theorem for this modality.
