by Stephen Denning
Prior to Kuhn, science was primarily seen as the steady accretion of new facts and relationships, one on top of the other.
Kuhn accepted that science experiences long periods of conceptual continuity and accretion. This is what he calls "normal science". However, it is punctuated by periods of revolutionary science with abrupt discontinuities, as the mental model changes in fundamental ways.
There are three distinct phases.
The first phase is a pre-paradigm phase in which there is no consensus on any particular theory. There may be several incompatible or incomplete theories.
The second phase occurs when a number of puzzles can be solved within a single mental framework or paradigm. This then becomes the dominant framework. Scientists gravitate to the new framework and normal science begins. There after, scientists try to solve to puzzles within the assumptions of the dominant paradigm. Most scientists spend their entire careers accepting the prevailing framework and proceed in a puzzle solving mode within its basic assumptions. It becomes unthinkable to view the world in any other way.
As times goes on however, anomalies appear that cannot be easily resolved within the dominant framework of assumptions. Yet, paradoxically, puzzle solving within the framework continues with even greater tenacity, because prior successes lead people to believe that resolving anomalies within the existing framework must be possible, even though solutions are hard to find.
Anomalies thus accumulate as the dominant paradigm is stretched and bent and adjusted in an increasingly desperate attempt to accommodate them yet with only partial success.
The third phase finally occurs when some scientists accept that the dominant framework cant resolve the anomalies. The scientists come to see that the basic framework cant be repaired. It must be replaced. They start exploring alternatives to long-held, seemingly obvious, self-evident assumptions and thus revolutionary science begins.
These scientists develop a new conceptual framework that they believe presents a better way of reconciling the known facts with the anomalies.
At first, the new framework itself has various gaps and contradictions because it is incomplete and needs further thought. When first presented, the new framework is greeted with hostility and derision from the establishment, people who's careers and lives have been based on the nurturing of the existing paradigm. The inevitable gaps and flaws of the new framework are cited for reasons for not adopting it.
Consequently, paradigm shifts do not occur quickly, or easily. There follows a period in which the adherents of different frameworks pursue their different theories.
The powers that be attack the revolutionary framework for being theoretically unsound, incomplete, and irresponsible, while the the revolutionaries point to the growing list of unresolved anomalies of the still-dominant paradigm.
In time, the gaps in the new framework are filled and the new framework is integrated and completed. Other scientists then converge on it as a more productive way of understanding how the world works. Once most scientists agree the new paradigm should replace the old, a paradigm shift has occurred, even though many individuals may remain intransigent and continue to think and teach in the old way.
As scientists look at the world in the new way, the direction of future scientific research in the field shifts. New questions are asked of old data. In due course, textbooks are rewritten and university courses are revised.
The period of conflict between frameworks may last for decades, especially if the new paradigm comes not from some of the existing leaders of the current scientific establishment, but rather from some peripheral, unexpected source.