  It is a common view in philosophy of physics that thermodynamics is a
non-fundamental theory. This is motivated in particular by the fact that
thermodynamics is considered to be a paradigmatic example for a theory that can
be reduced to another one, namely statistical mechanics. For instance, the
statement "temperature is mean molecular kinetic energy" has become a textbook
example for a successful reduction, despite the fact that this statement is not
correct for a large variety of systems. In this article, we defend the view
that thermodynamics is a fundamental theory, a position that we justify based
on four case studies from recent physical research. We explain how entropic
gravity (1) and black hole thermodynamics (2) can serve as case studies for the
multiple realizability problem which blocks the reduction of thermodynamics.
Moreover, we discuss the problem of the reducibility of phase transitions and
argue that bifurcation theory (3) allows the modelling of "phase transitions"
on a thermodynamic level even in finite systems. It is also shown that the
derivation of irreversible transport equations in the Mori-Zwanzig formalism
(4) does not, despite recent claims to the contrary, constitute a reduction of
thermodynamics to quantum mechanics. Finally, we briefly discuss some arguments
against the fundamentality of thermodynamics that are not based on reduction.
