Full Idea
In Hare's theory I apply a "role-reversal test", and then acquire an actual agglomeration of preferences that apply to the hypothetical situation. The result is utilitarianism.
Gist of Idea
Hare says I acquire an agglomeration of preferences by role-reversal, leading to utilitarianism
Source
report of Richard M. Hare (Moral Thinking: Its Levels,Method and Point [1981]) by Bernard Williams - Ethics and the Limits of Philosophy Ch.5
Book Reference
Williams,Bernard: 'Ethics and the Limits of Philosophy' [Fontana 1985], p.83
A Reaction
It hits that traditional stumbling block, of why I should care about the preferences of others. Pure reason and empathy are the options (Kant or Hume). I may, however, lack both.