  The Boltzmann distribution describes a single parameter (temperature) family
of probability distributions over a state space; at any given temperature, the
ratio of probabilities of two states depends on their difference in energy. The
same family is known in other disciplines (economics, psychology, computer
science) with different names and interpretations. Such widespread use in very
diverse fields suggests a common conceptual structure. We identify it on the
basis of few natural axioms. Checking whether observables satisfy these axioms
is easy, so our characterization provides a simple empirical test of the
Boltzmannian modeling theories.
