In 1962, Thomas Kuhn published "On the Structure of Scientific Revolutions", a book that forever changed the reading lists of philosophy of science classes around the world.
Kuhn based his argument on the case of Copernicus. Despite the mass of evidence arguing against the Ptolemaic model of the solar system, astronomers continued to find it self-evident, and to construct ever more elaborate explanations and excuses for its failures. Then, rather suddenly, belief in the old model collapsed, the Copernican model was taken up as the new paradigm, and no one could imagine how anyone had believed in the Ptolemaic model.
All advances in science occur this way, said Kuhn. Such sudden changes become known as "paradigm shifts", and this phrase, in turn, was suddenly widely bandied about and applied to hundreds of instances, small and large, where something, anything, changed.
In order to impose a sensible order on this chaotic landscape of paradigm shifts, a committe has been assembled, and assigned the task of developing the ISO Paradigm Shift Scale, whose fundamental unit is the kuhn, with the definition
1 kuhn = Copernican model - Ptolemaic model
that is, the paradigm shift from the Ptolemaic model to the
Copernican model registered 1.0 on the Kuhn scale. This is an
absolute scale, since a measurement of 0 kuhns indicates that
a model has not changed at all.
Generally speaking, most things that are commonly called "paradigm shifts" will have to be measured in significantly smaller units, such as:
The ISO has urged the universal adoption of this scale, which should make it possible to objectively compare the importance of the various paradigm shifts that are regularly reported.