  The BRST quartet mechanism is briefly reviewed. A special emphasis is given
to the distinction of perturbative versus non-perturbative quartets. The field
contents of the non-perturbative BRST quartets generated by transverse gluons
or quarks in Landau gauge are presented. Corresponding truncated Bethe-Salpeter
equations for the respective first daughter and second parent states are
derived. It is discussed in which sense these equations provide evidence for
the existence of bound states as daughter states in non-perturbative BRST
quartets. It is noted that within the scaling solution of functional approaches
the infrared divergence of the quark-gluon vertex is exactly the right one
tomake the respective Bethe-Salpeter equation infrared consistent.
