Positivism is an epistemological position that holds that the goal of knowledge is simply to describe the phenomena that we experience. The purpose of science is sticking to what we can observe and measure. Knowledge of anything beyond that is impossible. In the positivist view, the universe is deterministic. It operates by laws of cause and effect that we could discern if we apply the unique approach of the scientific method. Science is largely a mechanical affair. The key approach of the scientific method is the experiment, the attempt to discern natural laws through direct manipulation and observation.
However, since the middle part of the 20th century things have changed in our views of science. Probably the most important has been our shift away from positivism into what is called post-positivism. Postpositivism recognizes that the way scientists think and work and the way we think in our everyday life are not distinctly different. Scientific reasoning and common sense reasoning are essentially the same process. There is no difference in kind between the two, only a difference in degree. Postpositivism recognizes that all observation is fallible and has error and that all theory is revisable. Where the positivist believed that the goal of science was to uncover the truth, the post-positivist believes that the goal of science is to hold steadily to the goal of getting it right about reality, even though we can never achieve that goal.
Hacking, Ian. (1983). Representing and Intervening, Introductory Topics in the Philosophy of Natural Science, Cambridge, UK: Cambridge University Press.
Creswell, J.W. (2013). Qualitative inquiry & research design: choosing among the five approaches. Thousand Oaks, CA: Sage Publications, Inc.