  Light constituent quark masses and the corresponding dynamical quark masses
are determined by data, the Quark-Level Linear $\sigma$ Model, and infrared
QCD. This allows to define effective nonstrange and strange current quark
masses which reproduce the experimental pion and kaon masses very accurately,
by simple additivity. Moreover, the masses of the light scalar mesons
$\sigma(600)$ and $\kappa(800)$ can be obtained straightforwardly from the
constituent quark masses. In contrast, the usual nonstrange and strange current
quark masses employed by Chiral Perturbation Theory do not allow a simple
quantitative explanation of the pion and kaon masses.
