Musicological research of the Middle Ages has always been confronted with a strong domination of church testimonies, which lead towards the idea of the predominant importance of church music, both for the Middle Ages and for subsequent music developments in Europe. Based on research of singing, this study shows how church sources as testimonies of a relatively small but strong social group can be interpreted, and how the value of their messages within a society can be relativised. it is elaborated how the social features of the education, professionality and male gender of the clergy were decisive for the singing style, and how the theoretical construction of the 'ars' demanded for itself a higher evaluation than that for the 'musica vulgaris'. The features of the notion of 'ars' were valid as the modern notion of 'art' far into the 20th century. If they are to be understood as a historically created heritage, and thus relativised in meaning, this will at the same time lead both to the discovery of new relations in the writing of Mediaeval history and to new evaluations.