What has the optimal taxation paradigm taught us?

Mirrlees' 1971 article, An exploration in the Theory of Optimum Income Taxation is widely recognized as having shaped modern income tax theory. Mirrlees aims to find the principles that should govern income taxation by combining equity and efficiency objectives. The article's output is an optimal tax schedule. This working paper questions the relevance of the optimal taxation paradigm by returning to its origins in Mirrlees' article. Mirrlees' model is normative; it discusses what society should do. This paper argues that the paradigm is not convincing: people are not likely to change their views on policies based on this line of rea-soning. The model is hypotheticodeductive, but people usually have stronger ideas about the conclusions of the model in terms of marginal tax rates than about its hypothesis, in terms of a parameter for social preference for equality. Also, a normative model should be judged by its normative relevance, but the normative implications of the model itself are rarely discussed. The paradigm's success conditions have never been examined. The initial promise of Mirrlees was to disentangle normative and descriptive disagreements. It was never fulfilled.