  There exist four pion nucleon coupling constants, $f_{\pi^0, pp}$,
$-f_{\pi^0, nn}$, $f_{\pi^+, pn} /\sqrt{2}$ and $ f_{\pi^-, np} /\sqrt{2}$
which coincide when up and down quark masses are identical and the electron
charge is zero. While there is no reason why the pion-nucleon-nucleon coupling
constants should be identical in the real world, one expects that the small
differences might be pinned down from a sufficiently large number of
independent and mutually consistent data. Our discussion provides a rationale
for our recent determination $$f_p^2 = 0.0759(4) \, , \quad f_{0}^2 = 0.079(1)
\,, \quad f_{c}^2 = 0.0763(6) \, , $$ based on a partial wave analysis of the
$3\sigma$ self-consistent nucleon-nucleon Granada-2013 database comprising 6713
published data in the period 1950-2013.
