We provide an axiomatization of an additively separable social welfare function in the context of Harsanyi’s impartial observer theorem. To do this, we reformulate Harsanyi’s setting to make the lotteries over the identities the observer may assume independent of the social alternative....

In this paper we extend Harsanyi's impartial observer theorem by showing that the large domain of social lotteries can be significantly restricted – it is sufficient that the domain consists only of constant extended lotteries. Copyright Springer-Verlag Berlin Heidelberg 2003