  According to their specific star formation rate (sSFR), galaxies are often
divided into `star-forming' and `passive' populations. It is argued that the
former define a narrow `Main Sequence of Star-Forming Galaxies' (MSSF) of the
form $\sSFR(\Mstar)$, whereas `passive' galaxies feature negligible levels of
star formation activity. Here we use data from the Sloan Digital Sky Survey and
the Galaxy and Mass Assembly survey at $z<0.1$ to constrain the conditional
probability of the specific star formation rate at a given stellar mass. We
show that the whole population of galaxies in the local Universe is consistent
with a simple probability distribution with only one maximum (roughly
corresponding to the MSSF) and relatively shallow power-law tails that fully
account for the `passive' population. We compare the quality of the fits
provided by such unimodal ansatz against those coming from a double log-normal
fit (illustrating the bimodal paradigm), finding that both descriptions are
roughly equally compatible with the current data. In addition, we study the
physical interpretation of the bidimensional distribution across the
$M_*-\sSFR$ plane and discuss potential implications from a theoretical and
observational point of view. We also investigate correlations with metallicity,
morphology and environment, highlighting the need to consider at least an
additional parameter in order to fully specify the physical state of a galaxy.
