In Tonnies' usage an opinion expressed in public is not public opinion. Nor are opinion polls which reveal many publics with diverse opinions the same thing as general public opinion. The latter is defined by its consensual nature. It may be strong or weak. A firm public opinion is more characteristic of values and broad principles than of current events.
Firm opinion has a normative quality and exerts social pressure.
In the United States this field grew out of the work of Robert Park and Herbert Blumer at the University of Chicago. Park studied in Germany at the turn of the Century and wrote his thesis on the crowd and the public, although Tonnies does not refer to it here. A central concern of this field is to study the processes through which individuals come together to form a public with a common focus. Through interaction individuals grapple with how best to respond to novel or contentious situations lacking resolution, such as the disruption following a natural disaster or lack of agreement on a society s system of stratification. He noted the potential of the modern press system to eviscerate national borders and create a world culture and single market.