  We suggest a qualitative model of a high-$T_c$ superconductor, based on
considerations of thermodynamics of phase transitions. As an example, we
consider the Mott transition and classify 5 solid phases around it. In our
model, a combined electronic and structural instability causes segregation into
either neutral or charged phases. A charged precipitate with a quantized
electric charge is a collective excitation of electrons, stabilized by a
collective athermal displacement of ions; this local variation of the charge
density, accompanied by a local lattice deformation, can behave as a
quasi\-particle. A condensate of charged bosonic quasi\-particles is
responsible for the superconductivity.
