JJ Thompson (discoverer of electron) in 1916 said that pure science was one which was motivated by curiosity and a desire to learn more about the laws of nature. Applied science on the other hand is an attempt to answer specific questions. In Sociology too, this tussle between understanding society for its own sake, or to use that knowledge to reform society dates back to the beginning of the discipline. Thus sociology gas been identified with having two tasks:
Pure Sociology: to study the basic laws of social change and social structure
Applied Sociology: Involved the conscious use of this knowledge to attain a better society.
This dual purpose is evident from the works of early sociologists onwards. Comte and Durkheim were disturbed by the social unrest caused due to the French Revolution and Enlightenment. Comte developed social physics to understand social statics and social dynamics (the pure sociology part). This knowledge was to be used by sociology to assist in the ‘reforms’ that were propelling society towards the positivistic stage (the applied part of sociology).
Durkheim too, perturbed by the social disorder of his times (industrial strikes, church-state discord, political anti-Semitism), was driven to seek an improved understanding of society. He developed a research tool- ‘social fact’. Through this he identified the differences in earlier societies and modern societies. Durkheim argued that early societies were characterized by strong collective conscience (common morality) which provided cohesion to the society and support to its members. Alternatively modern societies had a weak collective conscience. This was the pure science part of his sociological theory. In applying this knowledge Durkheim argues that common morality could be strengthened in modern societies which would help people to cope better with the pathologies of their society.
For, feminist theorists the understanding of society is invariable succeeded by using the knowledge in social reform. This activism was as much part of their doing sociology as creating theory was.
Source: George Ritzer 2000, Sociological Theory