We lead our lives in the social or human domain, the sphere of human co-existence and interaction. More particularly our lives unfold within and through our membership of groups. Much effort, ink and no little passion has been expended in assessing the nature of social groups, their relationship with their individual members and their role in description, explanation, evaluation and practical reasoning. Our language and our understanding of the world appear unable to dispense with families, tribes, gangs, peoples, cultures, teams (sporting and work based), companies, religious bodies, bureaucracies, governments, political organisations, states, economic classes, social classes, mobs and crowds.1