In this paper we develop a di¤erentiable approach to deal with incentives in a, possibly small, subset of a general domain of preferences in economies with one public and one private good. We show that, for two agents, there is no mechanism which is e¢ cient, strategy-proof and where consumption of both goods is positive for all agents. For the case of two or more agents the same result occurs when nondictatorship is replaced by Individual Rationality.Journal of Economic Literature Classi…cation Numbers: D61, D78, H41.We are very grateful to