  We analyze the scaling and finite-size-scaling behavior of the
two-dimensional 4-state Potts model. We find new multiplicative logarithmic
corrections for the susceptibility, in addition to the already known ones for
the specific heat. We also find additive logarithmic corrections to scaling,
some of which are universal. We have checked the theoretical predictions at
criticality and off criticality by means of high-precision Monte Carlo data.
