Keywords: Churches in Modern State; Church and Deviance; Church and State in Late Middle Ages.
In modern times a plurality of religious communities are living together within a pluralist constitutional state, which is respectful for each of them. Otherwise in the middle ages: In the same manner as the social-political order of the kingdom presented the political structure of the whole community so presented the church its religious order. There was no plurality of different religious groups within the same people, only strangers and guests could be different. Therefore neither an interreligious dialogue nor an interconfessional 'ecumenism' could develop, particularly since different Christian 'confessions' are only a modern phenomenon. Thinking on 'unity' and 'union' of the church did only consider the problems of a 'schism' and or of heretical deviance. The essay shall persecute the criterias of unity in late medieval ecclesiology, mainly in later scholasticism from Thomas Aquinas to Nicolas of Cues. The philosophical instruments are taken into account, in order to look at the preconditions of unionist debates. Very seldom there we can see an opening for different attitudes and less still pluralistic freedom of organization. The medieval theory of unity for church and state does not seem to be a prospective way for future ecumenism.