  Based on the foundations of thermodynamics and the equilibrium conditions for
the coexistence of two phases in a magnetic Ising-like system, we show, first,
that there is a critical point where the isothermal susceptibility diverges and
the specific heat may remain finite, and second, that near the critical point
the entropy of the system, and therefore all free energies, do obey scaling.
Although we limit ourselves to such a system, we elaborate about the
possibilities of finding universality, as well as the precise values of the
critical exponents using thermodynamics only.
