Wikipedia: Post-normal science is a concept developed by Silvio Funtowicz and Jerome Ravetz, attempting to characterise a methodology of inquiry that is appropriate for cases where “facts are uncertain, values in dispute, stakes high and decisions urgent” (Funtowicz and Ravetz, 1991). It is primarily applied in the context of long-term issues where there is less available information than is desired by stakeholders.
According to a series of articles published between 1991 and 1993 post-normal science is simply an extension of situations routinely faced by experts such as surgeons or senior engineers on unusual projects, where the decisions being made are of great importance but where not all the factors are necessarily knowable. Although their work is based on science, such individuals must always cope with uncertainties, and their mistakes can be costly or lethal.
See also impact science, wicked problems, super-wicked problems