All human beings who possess a language have opinions on anything they have experienced, through direct sensory contact or through the words conveyed by others. Apparently, there may be only a short step from individual opinion to aggregates of opinion. But historically, the step is quite a giant one. And it is a matter of conceptual clarification and empirical observation to assess whether and how opinions perform a public function.

Public opinion requires that the public becomes both the subject and the object of shared beliefs. It grows out of major changes in the structure of the governmental apparatus constituting the public sphere, as well as in the rising of a new class of people determined to influence the public sphere with criticism and open-minded discussion. However, individual opinions, while a prerequisite for the forming of an informed public, can choose other channels of expression, the most relevant being electoral representation.

Two key factors account for the development and consolidation of a vigilant public opinion: strong and pluralistic media as both a source of information and a tribune for discussion, and the rational choice of individuals as the basic parameter of free and responsible judgement (ULQ). It has taken a five-centuries long process of intellectual progress and political adaptation for public opinion to fulfill its normative mission: the widespread mobilization of an informed citizenry to openly discuss and evaluate the running of governmental affairs. Yet, this also becomes the point where public opinion inevitably spills over into new directions - and quadrants - only partly coincident with the original idealtype. The first is the expansion of the voting franchise, which leads to alternative forms for representing individual orientations, through elections (LLQ) or referenda (LRQ). The second is the cultural massification of public opinion, which tends to be more and more perceived as - and reduced to - the sampling of a mere statistical aggregate (URQ). By providing an acceptable and credible method of measuring public opinion, polling could claim to be vox populi. Thus making a key democratic question all the more cogent: does the collective of opinion amount to more than the sum of all the opinions -- or less?