 A discussion of SM faces an immediate problem. Foundational debates in many other fields of physics can take as their point of departure a generally accepted formalism. Things are different in SM. Unlike, say, relativity theory, SM has not yet found a generally accepted theoretical framework, let alone a canonical  formulation.[12]  What we find in SM is plethora of different approaches and schools, each with its own programme and mathematical  apparatus.[13]  However, all these schools use (slight variants) of either of two theoretical frameworks, one of which can be associated with Boltzmann (1877) and the other with Gibbs (1902), and can thereby be classify either as ‘Boltzmannian’ or ‘Gibbsian’. For this reason we divide our presentation of SM into a two parts, one for each of these families of approaches.