Robert K. Merton in the context of "Merton Thesis"

In the social sciences, unintended consequences (sometimes unanticipated consequences or unforeseen consequences, more colloquially called knock-on effects) are outcomes of a purposeful action that are not intended or foreseen. The term was popularized in the 20th century by American sociologist Robert K. Merton.

Unintended consequences can be grouped into three types:

A sociological theory is a supposition that intends to consider, analyze, and/or explain objects of social reality from a sociological perspective, drawing connections between individual concepts in order to organize and substantiate sociological knowledge. Hence, such knowledge is composed of complex theoretical frameworks and methodology. These theories range in scope, from concise, yet thorough, descriptions of a single social process to broad, inconclusive paradigms for analysis and interpretation. Some sociological theories are designed to explain specific aspects of the social world and allow for predictions about future events, while others serve as broad theoretical frameworks that guide further sociological analysis. Dynamic social theory is the hypothesis that institutions and patterns of behaviour are the social science equivalent of theories in the natural sciences because they embody a great deal of knowledge of how society works and act as social models that are replicated or adapted to achieve predictable outsomes.

Prominent sociological theorists include Talcott Parsons, Robert K. Merton, Randall Collins, James Samuel Coleman, Peter Blau, Niklas Luhmann, Immanuel Wallerstein, George Homans, Theda Skocpol, Gerhard Lenski, Pierre van den Berghe and Jonathan H. Turner.

A self-fulfilling prophecy is a prediction that comes true at least in part as a result of a person's belief or expectation that the prediction would come true. In the phenomena, people tend to act the way they have been expected to in order to make the expectations come true. Self-fulfilling prophecies are an example of the more general phenomenon of positive feedback loops. A self-fulfilling prophecy can have either negative or positive outcomes. Merely applying a label to someone or something can affect the perception of the person/thing and create a self-fulfilling prophecy. Interpersonal communication plays a significant role in establishing these phenomena as well as impacting the labeling process.

American sociologists W. I. Thomas and Dorothy Swaine Thomas were the first Western scholars to investigate this phenomenon. In 1928, they developed the Thomas theorem (also known as the Thomas dictum): "If men define situations as real, they are real in their consequences." Another American sociologist, Robert K. Merton, continued the research, and is credited with coining the term "self-fulfilling prophecy" and popularizing the idea that "a belief or expectation, correct or incorrect, could bring about a desired or expected outcome." The works of philosophers Karl Popper and Alan Gewirth also contributed to the idea.

Jon Elster (/ˈɛlstər/; born 22 February 1940) is a Norwegian philosopher and political theorist who holds the Robert K. Merton professorship of Social Science at Columbia University and since 2005 professor of social science at the Collège de France.

He received his PhD in social science from the École Normale Superieure in 1972. He has previously taught at the University of Paris, the University of Oslo, and the University of Chicago, where he became professor of political science in 1984. Since 1995, he has held the Robert K. Merton professorship of Social Science at Columbia University, as well as being professor of social science at the Collège de France since 2005.

A role model is a person whose behaviour, example, or success serves as a model to be emulated by others, especially by younger people. The term role model is credited to sociologist Robert K. Merton, who hypothesized that individuals compare themselves with reference groups of people who occupy the social role to which the individual aspires, an example of which is the way young fans may idolize and imitate professional athletes or entertainment artists.

In the second half of the twentieth century, U.S. advocates for workplace equity popularized the term and concept of role models as part of a larger social capital lexicon—which also includes terms such as glass ceiling, networking, mentoring, and gatekeeper—serving to identify and address the problems barring non-dominant groups from professional success. Mainstream business literature subsequently adopted the terms and concepts, promoting them as pathways to success for all career climbers. In 1970 these terms were not in the general American vocabulary; by the mid-1990s they had become part of everyday speech. Although the term role model has been criticized more recently as "outdated", the term and its associated responsibility remains prominent in the public consciousness as a commonly used phrase, and a "powerful presence" in the entertainment industry and media.

Peter Michael Blau (February 7, 1918 – March 12, 2002) was an Austrian and American sociologist and theorist. Born in Vienna, Austria, he immigrated to the United States in 1939. He completed his PhD doctoral thesis with Robert K. Merton at Columbia University in 1952, laying an early theory for the dynamics of bureaucracy. The next year, he was offered a professorship at the University of Chicago, where he taught from 1953 to 1970. He also taught as Pitt Professor at Cambridge University in Great Britain, as a senior fellow at King's College, and as a Distinguished Honorary professor at Tianjin Academy of Social Sciences which he helped to establish. In 1970 he returned to Columbia University, where he was awarded the lifetime position of professor emeritus. From 1988 to 2000 he taught as the Robert Broughton Distinguished Research Professor at University of North Carolina, Chapel Hill in the same department as his wife, Judith Blau, while continuing to commute to New York to meet with graduate students and colleagues.

His sociological specialty was in organizational and social structures. He formulated theories relating to many aspects of social phenomena, including upward mobility, occupational opportunity, and heterogeneity. From each of his theories, he deduced an hypothesis which he would test against large scale empirical research. He was one of the first sociological theorists to use high level statistics to develop sociology as a scientific discipline using macro-level empirical data to gird theory. He also produced theories on how population structures can influence human behavior.

Opinion leadership is leadership by an active media user who interprets the meaning of media messages or content for lower-end media users. Typically opinion leaders are held in high esteem by those who accept their opinions. Opinion leadership comes from the theory of two-step flow of communication propounded by Paul Lazarsfeld and Elihu Katz. Significant developers of the opinion leader concept have been Robert K. Merton, C. Wright Mills and Bernard Berelson. This theory is one of several models that try to explain the diffusion of innovations, ideas, or commercial products.

Opinion leaders play an important role in information flow, because people tend to seek advice from others in the social environment. Information from the mass media does not directly flow to the target audiences, but through a mediation process, in which influential people digest the information and spread it to the public. Opinion leaders have certain characteristics that make them influential in the decision-making process and the behavior of the public. Through knowledge sharing, opinion leaders may help others do jobs better, facilitate personal development and improve personal recognition.