In his book The Commercialization of American Culture, Matthew P. McAllister says that "a well-developed media system, informing and teaching its citizens, helps democracy move toward its ideal state."
In 1997, J. R. Finnegan Jr. and K. Viswanath identified 3 main effects or functions of mass media:
The Knowledge Gap: The mass media influences knowledge gaps due to factors including "the extent to which the content is appealing, the degree to which information channels are accessible and desirable, and the amount of social conflict and diversity there is in a community".
Agenda Setting: People are influence in how they think about issues due to the selective nature of what media choose for public consumption. After publicly disclosing that he had prostate cancer prior to the 2000 New York senatorial election, Rudolph Giuliani, the mayor of New York City (aided by the media) sparked a huge priority elevation of the cancer in people's consciousness. This was because news media began to report on the risks of prostate cancer, which in turn prompted a greater public awareness about the disease and the need for screening. This ability for the media to be able to change how the public thinks and behaves has occurred on other occasions. In mid-1970s when Betty Ford and Happy Rockefeller, wives of the then-President and then-Vice President respectively, were both diagnosed with breast cancer. J. J. Davis states that "when risks are highlighted in the media, particularly in great detail, the extent of agenda setting is likely to be based on the degree to which a public sense of outrage and threat is provoked". When wanting to set an agenda, framing can be invaluably useful to a mass media organisation. Framing involves "taking a leadership role in the organisation of public discourse about an issue". The media is influenced by the desire for balance in coverage, and the resulting pressures can come from groups with particular political action and advocacy positions. Finnegan and Viswanath say, "groups, institutions, and advocates compete to identify problems, to move them onto the public agenda, and to define the issues symbolically" (1997, p. 324).
Cultivation of Perceptions: The extent to which media exposure shapes audience perceptions over time is known as cultivation. Television is a common experience, especially in places like the United States, to the point where it can be described as a "homogenising agent" (S. W. Littlejohn). However, instead of being merely a result of the TV, the effect is often based on socioeconomic factors. Having a prolonged exposure to TV or movie violence might affect a viewer to the extent where they actively think community violence is a problem, or alternatively find it justifiable. The resulting belief is likely to be different depending of where people live however.
Since the 1950s, when cinema, radio and TV began to be the primary or the only source of information for a larger and larger percentage of the population, these media began to be considered as central instruments of mass control. Up to the point that it emerged the idea that when a country has reached a high level of industrialization, the country itself "belongs to the person who controls communications."
Mass media play a significant role in shaping public perceptions on a variety of important issues, both through the information that is dispensed through them, and through the interpretations they place upon this information. They also play a large role in shaping modern culture, by selecting and portraying a particular set of beliefs, values, and traditions (an entire way of life), as reality. That is, by portraying a certain interpretation of reality, they shape reality to be more in line with that interpretation. Mass media also play a crucial role in the spread of civil unrest activities such as anti-government demonstrations, riots, and general strikes. That is, the use of radio and television receivers has made the unrest influence among cities not only by the geographic location of cities, but also by proximity within the mass media distribution networks.