Though scientists’ work relies on collecting empirical data, Thomas Kuhn’s treatise The Structure of Scientific Revolutions argues that scientists’ views of the world also play an important role, because their perceptions are what dictate which questions they ask and what they focus on in their research or experiments. As Kuhn sees it, each radically new scientific discovery ushers in a new way of perceiving the world—what Kuhn calls a paradigm—that the scientists in a given field agree on. But while Kuhn emphasizes that these paradigms are a useful way to solve problems, he also makes clear that a new paradigm is more like a fundamental shift in perception than an accumulation of knowledge that brings scientists closer to the truth. Kuhn therefore concludes that while scientists may find new ways of looking at new kinds of problems, they will never get closer to objective truth—and that, in fact, no such thing exists.
First, Kuhn shows how perception and belief are necessary in order to make any scientific work possible. Kuhn suggests that “the operations and measurements that a scientist undertakes in the laboratory are not ‘the given’ of experience but rather ‘the collected with difficulty.’” In other words, even to make basic decisions about what to write down from their experiments, scientists must make a great many decisions about what is important or useful. Kuhn argues that there is so much sensory information in the world that approaching it as a truly neutral observer is impossible. Instead, even when scientists believe they are being completely objective, they are in fact choosing to focus their attention on some data points at the expense of others. Crucially, Kuhn then emphasizes how that choice is guided by internal beliefs and values. Rather than depicting science as a collection of objective observations and experiments, Kuhn notes that “an apparently arbitrary element, compounded of personal and historical accident, is always a formative ingredient of the beliefs espoused by a given scientific community at a given time.” In other words, in order to decide what kind of questions to ask and techniques to use, scientists must draw on the “personal and historical” context of what is important to them. To illustrate his point, Kuhn draws on the metaphor of a Rorschach test in which there is a piece of paper with an ambiguous drawing on it. When held horizontally, the image on the paper looks like a bird, and there is no question about what kind of animal is one the paper. Similarly, when scientists draw on their innate, initial perceptions, they are looking through the world from a certain angle, and so their problems and solutions seem almost inevitable.
Using various moments in scientific history, Kuhn then posits that great discoveries always caused a fundamental shift in scientists’ perception of the world. In Kuhn’s metaphorical Rorschach test, the drawing initially appeared to be a bird—but when the paper is flipped 90 degrees, it suddenly appears to be an antelope. Kuhn argues that the same thing happened in the history of science when, for example, Copernicus’s discovery that the sun was at the center of the solar system transformed not only astronomists’ work but the very way they perceived the sky around them. That shift in experience, Kuhn explains, is why “paradigm changes do cause scientists to see the world of their research-engagement differently. In so far as their only recourse to that world is through what they see and do, we may want to say that after a [scientific] revolution scientists are responding to a different world.” When a bird becomes an antelope, or one’s understanding of the solar system is rearranged, the world as scientists perceive it is completely altered. Kuhn has made it clear that scientific engagement with the universe is always perceptual, so when scientific perception shifts, he then argues the universe itself becomes “different.” In emphasizing that paradigms are about shifts in perception, Kuhn is also careful to clarify that no one paradigm is better or more truthful than another. In his section on Galileo’s view of the pendulum, for example, Kuhn asks, “why did that shift of vision occur? Through Galileo’s individual genius, of course. But note that genius does not here manifest itself in more accurate or objective observation of the swinging body. Descriptively, the Aristotelian perception is just as accurate.” Though each paradigm involves a different set of perceptions, Kuhn is firm that one is not “more accurate or objective” than the other. Both merely involve different ways of looking at the same exact thing—and because it is impossible for humans to understand anything without looking at it, it is impossible to get a completely neutral observer who could declare whether Galileo’s view is better or worse than Aristotle’s.
Ultimately, then, Kuhn suggests that all science can offer is new paradigms of perception, not any objective truth. In one of the book’s most famous quotations, Kuhn blurs the line between myth and science: “if these out-of-date beliefs are to be called myths, then myths can be produced by the same sorts of methods and held for the same sorts of reasons that now lead to scientific knowledge. If, on the other hand, they are to be called science, then science has included bodies of belief quite incompatible with the ones we hold today.” Kuhn’s use of the word “myth” is particularly telling in this quotation; myths imply human feelings and narratives, while science suggests objective fact. But while scientists try to dismiss the conclusions of past eras, their own work is similarly dependent on instinct and intuition. Indeed, because all scientific language draws on particular points of focus or underlying beliefs, Kuhn believes that “language thus restricted to reporting a world fully known in advance can produce mere neutral and objective reports on ‘the given.’” In other words, no one can look at a pendulum swinging and view it without any lens or beliefs (which would be necessary for a “neutral and objective report”). And because no individual scientist can separate their particular view from what is actually happening, no scientific community will ever be able to articulate what is actually happening.
At the end of his treatise, therefore, Kuhn calls on his readers to “relinquish the notion, implicit or explicit, that changes of paradigm carry scientists and those who learn from them closer and closer to the truth.” If science can never be objective, one paradigm will always exclude the very facts that another paradigm holds dear; to put it in terms of Kuhn’s own metaphor, the Rorschach drawing can never be both bird and antelope at the same time, even though it contains both within it. Though it is radical, then, Kuhn’s final argument makes sense: science will hold great value, but it will never reach a solid, objective truth—perhaps because no such thing exists.
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Perception and Truth Quotes in The Structure of Scientific Revolutions
History, if viewed as a repository for more than anecdote or chronology, could produce a decisive transformation in the image of science by which we are now possessed.
If these out-of-date beliefs are to be called myths, then myths can be produced by the same sorts of methods and held for the same sorts of reasons that now lead to scientific knowledge. If, on the other hand, they are to be called science, then science has included bodies of belief quite incompatible with the ones we hold today.
No natural history can be interpreted in the absence of at least some implicit body of intertwined theoretical and methodological belief that permits selection, evaluation, and criticism. If that body of belief is not already implicit in the collection of facts—in which case more than “mere facts” are at hand—it must be externally supplied, perhaps by a current metaphysic, by another science, or by personal and historical accident. No wonder, then, that in the early stages of the development of any science different men confronting the same range of phenomena, but not usually all the same particular phenomena, describe and interpret them in different ways.
Mopping-up operations are what engage most scientists throughout their careers. They constitute what I am here calling normal science. Closely examined, whether historically or in the contemporary laboratory, that enterprise seems an attempt to force nature into the preformed and relatively inflexible box that the paradigm supplies. No part of the aim of normal science is to call forth new sorts of phenomena; indeed those that will not fit the box are often not seen at all.
There must also be rules that limit both the nature of acceptable solutions and the steps by which they are to be obtained. To solve a jigsaw puzzle is not, for example, merely “to make a picture.” Either a child or a contemporary artist could do that by scattering selected pieces, as abstract shapes, upon some neutral ground. The picture thus produced might be far better, and would certainly be more original, than the one from which the puzzle had been made. Nevertheless, such a picture would not be a solution. To achieve that all the pieces must be used, their plain sides must be turned down, and they must be interlocked without forcing until no holes remain.
That process of learning by finger exercise or by doing continues throughout the process of professional initiation […] One is at liberty to suppose that somewhere along the way the scientist has intuitively abstracted rules of the game for himself, but there is little reason to believe it. Though many scientists talk easily and well about the particular individual hypotheses that underlie a concrete piece of current research, they are little better than laymen at characterizing the established bases of their field, its legitimate problems and methods.
An investigator who hoped to learn something about what scientists took the atomic theory to be asked a distinguished physicist and an eminent chemist whether a single atom of helium was or was not a molecule. Both answered without hesitation, but their answers were not the same. For the chemist the atom of helium was a molecule because it behaved like one with respect to the kinetic theory of gases. For the physicist, on the other hand, the helium atom was not a molecule because it displayed no molecular spectrum. Presumably both men were talking of the same particle, but they were viewing it through their own research training and practice. Their experience in problem-solving told them what a molecule must be.
Philosophers of science have repeatedly demonstrated that more than one theoretical construction can always be placed upon a given collection of data. History of science indicates that, particularly in the early developmental stages of a new paradigm, it is not even very difficult to invent such alternates. But that invention of alternates is just what scientists seldom undertake […] The reason is clear. As in manufacture so in science—retooling is an extravagance to be reserved for the occasion that demands it. The significance of crises is the indication they provide that an occasion for retooling has arrived.
When acute, this situation is sometimes recognized by the scientists involved. Copernicus complained that in his day astronomers were so “inconsistent in these [astronomical] investigations . . . that they cannot even explain or observe the constant length of the seasonal year.” “With them,” he continued, “it is as though an artist were to gather the hands, feet, head and other members for his images from diverse models, each part excellently drawn, but not related to a single body, and since they in no way match each other, the result would be monster rather than man.” Einstein, restricted by current usage to less florid language, wrote only, “It was as if the ground had been pulled out from under one, with no firm foundation to be seen anywhere, upon which one could have built.”
The marks on paper that were first seen as a bird are now seen as an antelope, or vice versa. That parallel can be misleading. […] the scientist does not preserve the gestalt subject’s freedom to switch back and forth between ways of seeing. Nevertheless, the switch of gestalt, particularly because it is today so familiar, is a useful elementary prototype for what occurs in full-scale paradigm shift.
Examining the record of past research from the vantage of contemporary historiography, the historian of science may be tempted to exclaim that when paradigms change, the world itself changes with them. Led by a new paradigm, scientists adopt new instruments and look in new places. Even more important, during revolutions scientists see new and different things when looking with familiar instruments in places they have looked before. […] In so far as their only recourse to that world is through what they see and do, we may want to say that after a revolution scientists are responding to a different world.
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.”
But is sensory experience fixed and neutral? Are theories simply manmade interpretations of given data? The epistemological viewpoint that has most often guided Western philosophy for three centuries dictates an immediate and unequivocal, Yes! In the absence of a developed alternative, I find it impossible to relinquish entirely that viewpoint. Yet it no longer functions effectively, and the attempts to make it do so through the introduction of a neutral language of observations now seem to me hopeless. The operations and measurements that a scientist undertakes in the laboratory are not “the given” of experience but rather “the collected with difficulty.”
Chemists could not, therefore, simply accept Dalton’s theory on the evidence, for much of that was still negative. Instead, even after accepting the theory, they had still to beat nature into line, a process which, in the event, took almost another generation. When it was done, even the percentage composition of well-known compounds was different. The data themselves had changed. That is the last of the senses in which we may want to say that after a revolution scientists work in a different world.
These examples point to the third and most fundamental aspect of the incommensurability of competing paradigms. In a sense that I am unable to explicate further, the proponents of competing paradigms practice their trades in different worlds. One contains constrained bodies that fall slowly, the other pendulums that repeat their motions again and again. In one, solutions are compounds, in the other mixtures. One is embedded in a flat, the other in a curved, matrix of space.
Though a generation is sometimes required to effect the change, scientific communities have again and again been converted to new paradigms. Furthermore, these conversions occur not despite the fact that scientists are human but because they are.
We may, to be more precise, have to relinquish the notion, explicit or implicit, that changes of paradigm carry scientists and those who learn from them closer and closer to the truth.
The law-sketch, say f = ma, has functioned as a tool, informing the student what similarities to look for, signaling the gestalt in which the situation is to be seen […] After he has completed a certain number, which may vary widely from one individual to the next, he views the situations that confront him as a scientist in the same gestalt as other members of his specialists’ group. For him they are no longer the same situations he had encountered when his training began. He has meanwhile assimilated a time-tested and group-licensed way of seeing.
