 Sen (1970b) and Gibbard (1974) propose, within the framework of social choice, paradoxes showing that it may not be easy to rank alternatives when some individuals have a special right to rank some alternatives that differ only in matters belonging to their private sphere, and when their preferences are sensitive to what happens in other individuals’ private spheres. For instance, as an illustration of Gibbard’s paradox, individuals have the right to choose the color of their shirt, but, in terms of social ranking, should A and B wear the same color or different colors, when A wants to imitate B and B wants to have a different color? There is a huge literature on this topic, and after Gaertner, Pattanaik and Suzumura (1992), who argue that no matter what choice A and B make, their rights to choose their own shirt is respected, a good part of it examines how to describe rights properly. The framework of game forms is an interesting alternative to the social choice model. Recent surveys can be found in Arrow, Sen and Suzumura (1997, vol. 2).