A paradigm, in the context of theory and research, is a particular and accepted set of thoughts and assumptions about the way things are and the way research should be done. Thomas Kuhn, an American scientist, argued that the way most people see science is not quite accurate. It is not purely objective – at a particular point in time scientific research is done in a particular paradigm. Mainstream science therefore accepts the assumptions of that paradigm and views its conclusions within those basic assumptions. While it does that, there will be "radical science" that challenges those assumptions and it is possible for there to be a paradigm shift, and the radical science to become the new mainstream. So now scientists view their evidence with assumptions such as evolution and gravity taken for granted (just as scientists once took it for granted that the Earth was in the centre of the universe, or even that the Earth was flat).
As such, Kuhn argues that sociology is not a mature, mainstream science, because it hasn't found a unifying paradigm. Sociologists do not share a set of assumptions about the world or about how to do research. There are functionalists and Marxists, there are positivists and interpretivists. He concludes then that sociology is a "young science" but that it could in the future coalesce around one paradigm and become a science. However, it is a concept of science that differs significantly from that of positivist sociologists.