Thomas Kuhn’s The Structure of Scientific Revolutions

I just finished listening to Thomas Kuhn’s The Structure of Scientific Revolutions. Yes, I said listening. Living in Boston, you walk everywhere and I have tried to maximize my efficiency in my scholarly pursuits by using that walking time (up to three hours each day) by listening to audiobooks. Some books are more difficult to listen to than others. The Structure of Scientific Revolutions was one of the easier ones.

Most generally, the book (or “essay,” as Kuhn calls it in the preface) is a work in the philosophy of science which is trying to explain how scientific knowledge, and more specifically, scientific theory, develops. Kuhn is adamant that scientific theories do not emerge as the product of a mere accumulation of scientific facts and data. Rather, new theories emerge as products of changing circumstances and and a new intellectual milieu. New theories are the expressions of a new way of seeing, of perceiving the world.

The framework in which a scientist perceives the world is what Kuhn calls a paradigm, and a shift in perception leading to a new way of perceiving the world is called a paradigm shift. A paradigm shift is the result of an anomaly, a failure of a paradigm to explain certain phenomena. For example, in the Ptolemaic universe, the solar system was made up of a series of concentric circles with Earth as its center and the planets moving in perfect circles around the earth. This was a paradigm, a way of seeing the world. According to this way of seeing the world, Mars appears to go backwards in the night sky, what astronomers call retrograde motion. This discrepancy in observed astronomical data could only be explained with the development of a new heliocentric (Copernicus) solar system with elliptical orbits (Kepler). This paradigm shift is literally a new way of seeing the solar system and indeed the entire universe. The knowledge that Mars is not actually going backwards is not just the accumulation of new knowledge but a new mode of perception.

Kuhn basic insight is a psychological one–the expectations we bring into our observations influences our conclusions. He cites an interesting experiment in which subjects were quickly shown the playing cards of ordinary deck except for certain cards in which the suit of a certain color was exchanged for its opposite. So, for example, a subject might be shown a red three of clubs or a black king of hearts. The subjects overwhelmingly identified the card according to color–what they expected to see. So instead of correctly identifying the card as a king of hearts (despite its black color), the subjects would say “king of spades,” changing the suit according to what they expected to see. The more they were exposed to the anomalous card, the more uncertain they would become, but at first, what they saw matched their expectations, or in Kuhn’s language, their paradigm–black curvy suits are spades, not hearts, and are identified accordingly. The moral: our expectations shape what we see. Two scientists immersed in two different paradigms can observe the same phenomena and actually see two totally different phenomena.

Scientific knowledge is a lot like this, according to Kuhn. New scientific knowledge and new theories are not just the result of an increase in knowledge (though this is certainly a part of it, as more refined tools for observation are developed). But to even develop new tools, we have to know what it is that we are measuring. So new knowledge is not just the result of better tools, but rather, the result of shifts in perception, the ability to see what we once thought was a duck as a rabbit, to cite the example Kuhn himself uses. In another example, Kuhn cites an experiment where a person wears certain glasses which flip her vision, causing her to see everything upside down. Within a few minutes, her vision adapts, allowing her to see everything right side up. A person wearing the inverting lenses and a person not wearing the inverting lenses would then see the world in exactly the same way despite the fact that each had two opposite retinal impressions (one right side up, the other upside down). If the person were to take off the inverting lenses, at first, she would see everything upside down again, until her vision re-adapted. At this point, she and the person who had never had the inverting lenses on would see two different things (one right side up, the other upside down), despite having the same retinal impressions.

What Kuhn wants us to take away from the text is that there is no such thing as purely objective or purely neutral observational language. Scientists don’t get to claim that they just “examine the facts.” The “facts” are always products of perception. Some may call this relativism, but at least at this point, I would disagree. I think its a nice way of introducing epistemic humility into the sciences.

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