So a phase transition occurs when a system may minimize its free energy by spontanously breaking some symmetry. At least that is what I have learnt from my current course so far. However I also did another course concerning phase transitions. In this case phase transitions were always explained by some kind of instability, e.g. the divergence of for instance the electric susceptibility function χ. How does all this go together with the interpretation of spontanous symmetry breaking as caused by minimizing the free energy?