Also called a paradigm shift, Paradigm change is the fifth and final step in the Kuhn Cycle. Earlier steps have created the new model of understanding (the new paradigm). In the Paradigm Change step the new paradigm is taught to newcomers to the field, as well as to those already in it. When the new paradigm becomes the generally accepted guide to one's work, the step is complete. The field is now back to the Normal Science step and a Kuhn Cycle is complete.
Why Paradigm Change is usually slow
People and systems resist change. They change only when forced to or when the change offers a strong advantage. If a person or system is biased toward its present paradigm, then a new paradigm is seen as inferior, even though it may be better. This bias can run so deep that two paradigms are incommensurate. They are incomparable because each side uses their own paradigm's rules to judge the other paradigm. People talk past each other. Each side can "prove" their paradigm is better.
Writing in his chapter on The Resolution of Revolutions, Thomas Kuhn states that: (pages 147 to 148)
If there were but one set of scientific problems, one world within which to work on them, and one set of standards for their solution, paradigm competition might be settled more or less routinely by some process like counting the number of problems solved by each.
But in fact these conditions are never met. The proponents of competing paradigms are always at least slightly at cross-purposes. Neither side will grant all the non-empirical assumptions that the other needs in order to make its case. Like Proust and Berthollet arguing about the composition of chemical compounds, they are bound partly to talk through each other.
Though each may hope to convert the other to his way of seeing his science and its problems, neither may hope to prove his case. The competition between paradigms is not the sort of battle that can be solved by proofs.
We have already seen several reasons why the proponents of competing paradigms must fail to make complete contact with each other's viewpoints. Collectively these reasons have been described as the incommensurability of the pre and post revolutionary Normal Science traditions....
Actually the incommensurate paradigms problem applies mostly to the Model Revolution step. But if incommensurability is acute the delay it causes spills out into the Paradigm Change step, slowing it down considerably.
The larger the difference between two paradigms, the slower the Model Revolution and Paradigm Change steps usually are.
An example of long Paradigm Change
In Business Dynamics: Systems Thinking and Modeling for a Complex World, John Sterman documented how long it took Paradigm Change to come to the British merchant marine: (page 19)
Prior to the 1600s, scurvy (vitamin C deficiency) was the greatest killer of seafarers—more than battle deaths, storms, accidents, and all others combined.
1601: Lancaster conducts a controlled experiment during an East India Company voyage. The crew on one ship received 3 tsp. of lemon juice daily; the crew on the other ships did not. Results: At the Cape of Good Hope 110 out of 278 sailors had died, most from scurvy. The crew receiving the lemon juice treatment remained largely healthy.
1747: Dr. James Lind conducts a controlled experiment in which scurvy patients were treated with a variety of elixirs. Those receiving citrus were cured in a few days. None of the other treatments worked.
1795: The British Royal Navy begins using citrus on a regular basis. Scurvy wiped out. [Just in the navy]
1865: The British Board of Trade mandates citrus use. Scurvy wiped out in the merchant marine.