  We elucidate constraints imposed by confinement and dynamical chiral symmetry
breaking on the infrared behaviour of the dressed-quark and -gluon propagators,
and dressed-quark-gluon vertex. In covariant gauges the dressing of the gluon
propagator is completely specified by P(k^2):= 1/[1+Pi(k^2)], where Pi(k^2) is
the vacuum polarisation. In the absence of particle-like singularities in the
dressed-quark-gluon vertex, extant proposals for the dressed-gluon propagator
that manifest P(k^2=0)=0 and Max[P(k^2)]~10 neither confine quarks nor break
chiral symmetry dynamically. This class includes all existing estimates of
P(k^2) via numerical simulations.
