  A phenomenological approach to the ferromagnetic two dimensional Potts model
on square lattice is proposed. Our goal is to present a simple functional form
that obeys the known properties possessed by the free energy of the q-state
Potts model. The duality symmetry of the 2D Potts model together with the known
results on its critical exponent {\alpha} allow to fix consistently the details
of the proposed expression for the free energy. The agreement of the analytic
ansatz with numerical data in the q=3 case is very good at high and low
temperatures as well as at the critical point. It is shown that the q>4 cases
naturally fit into the same scheme and that one should also expect a good
agreement with numerical data. The limiting q=4 case is shortly discussed.
