It is argued that social representations and similar constructs can only be conceived of as mental structures containing meta-information about the group, within which the representation was formed and where it is part of social identity. The most important information will be to know the limits of its validity, that is, to know to which social group a representation pertains. Experiments on social projection have shown that people tend to project their opinions onto others, if they are perceived as being similar in background values. Such projection cannot be expected with idiosyncratic attitudes and beliefs. Consequently it is hypothesized that idiosyncratic and private attitudes, opinions, etc., are not attributed to specific social groups, whereas knowledge pertaining to social representations the subject subscribes to is projected onto the ingroup and less on the outgroup. This effect is expected to be independent of the relative number of people holding this opinion. This is what was found in a quasi-experimental questionnaire study. Implications of the findings are discussed with regard to the definition and criteria ofsociul representations and to the structure of the theory.