Public opinion is the sum of individual opinions, that interconnect in various ways using the tools of communication: in this way each person becomes maker of the decisions of those who represent them.

According to Professor Luciana Giacheri Fossati the concept of public opinion can be used to denote the set of ideas that a particular human agglomeration (city, nation, group of nations) feels right and true at a given time; it is the set of people which make up the community judging the facts that happen, based on the cultural, social, religious and economic references. It is an expression that refers, therefore, to a complex and ambivalent concept and that, according to the contexts, can vary and assume different meanings and senses.

The theme of the relationship between the public and private spheres, with all its implications as the crux of the relationship between morality and politics, from that moment begins to take on a central role. One of the first thoughts dates back to the English philosopher J. Locke. In his ‘Essay on human intelligence’,  he attributed to public opinion a control function of society, establishing a clear distinction between the moral law, expressed by the classes, and the civil law, issue of political power, distinction then picked up by I. Kant, who stressed on the public use of reason in all fields.

In 1922 the American sociologist W. Lippmann published the essay ‘Public opinion’, in which he examined the relationship established in advanced societies between a public becoming increasingly differentiated and the media. In this regard he noted that necessarily "what the individual does is based not on direct and confident knowledge , but on images that he forms or he is given."

The pioneering work of Lippmann was then taken up in the sixties by Habermas, a member of the Frankfurt School, in a context strongly characterized by increasing dynamic competition of the media. In his work, ‘Structural Transformation of the Public’ (1962), Habermas analyzes the transformation of the public sphere, from the point of view of the welfare state and changes in the structures of communication, under the influence of the media (press, radio, cinema and television). Habermas examined the transformation  in advanced industrial societies of the boundary between public and private spheres which tends increasingly to thin, while the public more and more loses its democratic value because of the continuous influence of the media.

Kant, laid stress, in particular, on the public space in which people make public use of their private reason against the absolutist power becoming the necessary condition of a rationalization policy in the name of morality.

The work of demystification of public opinion that will take place starting from the late nineteenth century, is considered generally prepared by authors such as Tocqueville and J.S.Mill. If the power gained by the public represented for the Enlightenment thinkers the end of the reign of coercion and violence and the advent of government by means of argument and persuasion, to Tocqueville and Mill, the domination of general opinion has its specific coercive force. To say that it now rules the world is equivalent to saying that the mass and general mediocrity exerts a constant moral violence on minorities.

From an instrument of emancipation, public opinion, no longer an emanation of the public of private educated of the eighteenth century, but of an amorphous and undifferentiated mass, seems to become an instrument of integration rather than criticism.

To mark the beginning of the process of degeneration of the public sphere is, according to Habermas, the transformation of civil society intervened in the late nineteenth century with the decline of the autonomy of the social thrust of state intervention, requested by the entrance of the mass in the political activity and by a new phase of capitalist development. With the invasion of society by the administrative state, the relationships between public and private will reshape, with phenomena such as the publicizing of privacy and the privatization of the public domain. A further boost to the degradation of the latter, starting in the same period, is the gradual subjugation of the press and publishing laws of a mass market, which is reflected in the general lowering of the cultural level of the newspapers and periodicals, and the trend towards de-politicization of the messages they conveyed.

However, are the social sciences in the late nineteenth and early twentieth century which attack harder against the eighteenth-century concept of public opinion. The social psychology of Sighele, Tarde, Le Bon, McDougall, the behaviorism of Watson and the analysis of democracy by authors such as Bryce and Ostrogorsky combine to redefine the limits of democratic governments just starting from the difficulty of keeping the idea of a public opinion, critical or illuminated.

Among these protagonists of the social sciences in the late nineteenth century, a special place in the history of the concept of public opinion is certainly recognized to Tarde. Breaking away from what was the then prevailing scientific orientation, Tarde will be the first to distinguish the phenomenon of the crowd from the public and identify in the latter the true protagonist of the story take place, and reconnecting the power and the expansion to the spread increasingly universal of the press. The assessment of the phenomenon is interesting for the ambivalence that he tends to emphasize: on the one hand, he tracks in the public the same mechanisms of imitation and suggestion active in the crowds, on the other he will highlight the character more thoughtful and fragmented because anyone can be a member simultaneously of a multiplicity of classes. For these aspects the audience is, in the eyes of Tarde, a form of sociality more evolved than the crowd: it  is its character of intellectual phenomenon to make room for an evaluation not necessarily negative.

If the discredit of public opinion is, in part, due to the confidence in scientific knowledge, some of the contemporary attempts to re-evaluate the space of the feasible are certainly due to the difficulties in which we find the scientific language when it comes to addressing issues that are linked in particular to the beginning and end of life. Scientific language shows in these areas, and, more generally, in the political sphere, a lack of power in communication. It tends, in fact, to hide, and sometimes to deny, that the scientific practices involve choices of value. The program of a dialogue between experts and the public, between the demands of critical instance and the strength of beliefs, has found some form of construction with the creation of bioethics committees and associative movements challenging in the context of ecology.

Although the role of ethics committees remains controversial, the communication model to which they are based is that of a public space that involves an equal comparison between ordinary knowledge, resulting from the experience and knowledge of various kinds, even of a humanistic nature.