A contribution to the theory of optimal utilitarian income taxation

The paper provides a new formulation of the Mirrlees–Seade theorem on the positivity of the optimal marginal income tax, under weaker assumptions and in a more general model. The formulation of the theorem is independent of whether the model involves finitely many types or a continuous type distribution. The formal argument makes the underlying logic transparent, relating the mathematics to the economics and showing precisely how each assumption enters the analysis.