  Active galactic nuclei (AGNs) form two distinct sequences on the
radio-loudness -- Eddington-ratio plane. The `upper' sequence contains radio
selected AGNs, the `lower' sequence is composed mainly of optically selected
AGNs. The sequences mark the upper bounds for the radio-loudness of two
distinct populations of AGNs, hosted respectively by elliptical and disk
galaxies. Both sequences show the same dependence of the radio-loudness on the
Eddington ratio (an increase with decreasing Eddington ratio), which suggests
that another parameter in addition to the accretion rate must play a role in
determining the efficiency of jet production in AGNs. We speculate that this
additional parameter is the spin of the black hole, assuming that black holes
in giant elliptical galaxies have (on average) much larger spins than black
holes in disc galaxies. Possible evolutionary scenarios leading to such a spin
dichotomy are discussed. The galaxy-morphology related radio-dichotomy breaks
down at high accretion rates where the dominant fraction of luminous quasars
being hosted by giant ellipticals is radio quiet. This indicates that the
production of powerful jets at high accretion rates is in most cases suppressed
and, in analogy to X-ray binary systems (XRB) during high and very high states,
may be intermittent. Such intermittency can be caused by switches between two
different accretion modes, assuming that only during one of them an outflow
from the central engine is sufficiently collimated to form a relativistic jet.
