Chapter X of Kuhn, Structure of scientific revolutions (p. 53 - 56)
When a scientific-revolution occurs, scientists don’t just adopt new theories, they begin to work in a different world. Kuhn means that the experienced reality of scientific work genuinely changes, even though the physical stimuli reaching the scientist remain the same.
“when a paradigm changes, the world itself changes with them.”
World-change follows from theory-ladenness-of-observation that what we observe depends and changes based on our paradigms, and explains incommensurability of paradigms; if scientists inhabit different worlds and cannot appeal to shared observations, then different paradigms become incomparable. Scientists are literally talking about different worlds.
Examples
- Discovery of Uranus
- Herschel identifies Uranus as comet, and then Lexell identifies it as a planet after at least 17 different occasions on which a “star” had been observed in same location as Uranus
- Kuhn calls this a minor paradigm shift which allows 20 new minor planets (asteroids) identified
- Western astronomers first observe change in heavens (e.g., sunspots, comets, new stars) in 50 years after Copernicus (after the paradigm that the stars were not perfect)
Comparing to Gestalt switches
Kuhn uses compares paradigm shifts to Gestalt switches to illustrate world change.
Gestalt switch = an sudden involuntary shift in perception where an ambiguous stimulus is instantly reorganized by the brain from one coherent image to another, even though the image remains unchanged.
E.g. the duck-rabbit illusion = the lines on the page remains the same but it appears as a duck in one instant and a rabbit in another
Similarly, when paradigms change, scientists do not simply reinterpret fixed date, instead they begin to “see” phenomena differently.
“What were ducks in the scientist’s world before the revolution are rabbits afterwards.” (Kuhn, p. 111)
“Therefore, at times of revolution, when the normal-scientific tradition changes, the scientist’s perception of his environment must be re-educated—in some familiar situations he must learn to see a new gestalt. After he has done so the world of his research will seem, here and there, incommensurable with the one he had inhabited before.” (Kuhn, p. 112)
where the analogy breaks down
“The subject of a gestalt demonstration knows that his perception has shifted because he can make it shift back and forth repeatedly while he holds the same book or piece of paper in his hands. Aware that nothing in his environment has changed, he directs his attention increasingly not to the figure (duck or rabbit) but to the lines on the paper he is looking at … With scientific observation, however, the situation is exactly reversed. The scientist can have no recourse above or beyond what he sees with his eyes and instruments.” (Kuhn, p. 114)
Gestalt switches are reversible at will, but scientists are unable to switch back to discard paradigms. Kuhn gives a good example for this:
Looking at the moon, the convert to Copernicanism does not say, “I used to see a planet, but now I see a satellite.” That locution would imply a sense in which the Ptolemaic system had once been correct. Instead, a convert to the new astronomy says, “I once took the moon to be (or saw the moon as) a planet, but I was mistaken.” (Kuhn, p. 115)