  In the radio - host galaxy optical luminosity plane FR I and FR II
radio-galaxies are clearly divided. Since the optical luminosity of an
elliptical galaxy is an indication of the mass of its central black hole, we
propose that the FR I - FR II dividing luminosity is a function of the mass of
the black hole powering the active nucleus. Furthermore, as the radio power
gives an estimate of the total kinetic power carried by the jet, the FR I - FR
II separation can be re-interpreted as occurring at a constant ratio between
the jet power and the black hole mass. There is also convincing evidence of a
correlation between the radio power and the luminosity in narrow emission
lines. As the latter results from photoionization by the radiation produced by
accretion, we can estimate the ionizing luminosity and find that the separation
luminosity can be also re-expressed as a constant accretion rate between
\~0.01-0.001 of the Eddington one. This possibly regulates the accretion mode
and the consequent presence and characteristics of nuclear outflows.
