We define the empirical content of an economic theory as the least restrictive observationally equivalent theory. We show that the empirical content of a theory is captured by a certain kind of axiomatization, with axioms that are universal negations of conjunctions of atomic formulae.

We explore the implications of four natural axioms in taxation: continuity (small changes in the data of a taxation problem should not lead to large changes in the tax allocation), equal treatment of equals (agents with the same pre-tax incomes pay equal taxes), consistency (the way in which a...