  We test the hypothesis that radio galaxies are a random subset of otherwise
normal elliptical galaxies. Starting with the observed optical luminosity
functions for elliptical galaxies, we show that the probability of an
elliptical forming a radio source is a continuous, increasing function of
optical luminosity, proportional to L squared. With this probability function
and the luminosity function of normal elliptical galaxies as input to Monte
Carlo simulations, we reproduce the observed distribution of radio galaxies in
the radio-optical luminosity plane. Our results show that radio galaxies are a
luminosity-biased but otherwise random sample of elliptical galaxies. This
unified view of radio-loud and radio-quiet ellipticals also explains the well
known difference of ~0.5 mag in average optical luminosity between FRI and FRII
radio galaxies as a simple selection effect. Specifically, FRII appear
preferentially in smaller galaxies because both radio and optical luminosity
functions are steep, so there is a negligible probability of observing a
powerful radio source associated with a bright galaxy; no intrinsic physical
differences between FRI and FRII host galaxies are required.
