  The axial-vector Ward-Takahashi identity is used to derive mass formulae for
neutral pseudoscalar mesons. Flavour symmetry breaking entails non-ideal
flavour content for these states. Adding that the \eta^\prime is not a
Goldstone mode, exact chiral-limit relations are developed from the identity.
They connect the dressed-quark propagator to the topological susceptibility. It
is confirmed that in the chiral limit the \eta^\prime mass is proportional to
the matrix element which connects this state to the vacuum via the topological
susceptibility. The implications of the mass formulae are illustrated using an
elementary dynamical model, which includes an Ansatz for that part of the
Bethe-Salpeter kernel related to the non-Abelian anomaly. In addition to the
current-quark masses, the model involves two parameters, one of which is a
mass-scale. It is employed in an analysis of pseudoscalar- and vector-meson
bound-states. While the effects of SU(N_f=2) and SU(N_f=3) flavour symmetry
breaking are emphasised, the five-flavour spectra are described. Despite its
simplicity, the model is elucidative and phenomenologically efficacious; e.g.,
it predicts \eta-\eta^\prime mixing angles of ~ (-15 degrees) and \pi^0-\eta
angles of ~ 1 degree.
