How to read Thomas Kuhn’s “The Structure of Scientific Revolutions”

The historian and philosopher of science Thomas Kuhn’s book The Structure of Scientific Revolutions is one of the most influential books of the 20th century. While I think it is a fantastic book, it also is a subtle one with layers I didn’t see until much later, and not in small part because of excellent guidance. I thought it might be useful if the structure of the book itself was presented, without the numerous scientific examples, and with a particular stress on what I believe Kuhn is aiming at along the way.

I. What is Kuhn upto?

A good place to begin is to ask what exactly Kuhn is arguing against, what his book is a response to. The answer to this can be found in the Introduction itself. He notices that scientists at every level are introduced to their various fields through textbooks, and the chief purpose of these books is to inform people of the latest developments. Since their purpose is to help create more scientists who will further progress, the history of science included in textbooks tends to be a superficial one that merely offers a gloss of the past, with past science portrayed as straightforwardly leading up to the current state of affairs. Dates, names, and discoveries may be mentioned, but in ways that suggest a kind of inexorable progress. While the ideas of previous scientists not believed to be wrong may be mentioned, it is usually without much importance and even sometimes to further bask in the certainty of progress (“even Newton believed in alchemy!”).

Thanks to this tendency towards superficial history, scientists can see themselves as the intellectual heirs of the giants of the past, not just in the generic sense of being interested in the truth, but as pursuers of similar questions itself.

In opposition to this view of science and its “history” as one of accumulation and progress, Kuhn observes that as historians of science learn more and more about the past, the harder it becomes to reconcile the complexities of what they find with the simple narrative textbooks teach.

The more carefully they study, say, Aristotelian dynamics, phlogistic chemistry, or caloric thermodynamics, the more certain they feel that those once current views of nature were, as a whole, neither less scientific nor more the product of human idiosyncrasy than those current today. If these out-of-date beliefs are to be called myths, then myths can be produced by the same sorts of methods and held for the same sorts of reasons that now lead to scientific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. Given these alternatives, the historian must choose the latter. Out-of- date theories are not in principle unscientific because they have been discarded.

In short, Kuhn urges us to take seriously the science of the past on its own terms to understand the nature of science and scientific change. The aim, as two historians put it, is to engage with “the specificity of the past, not with its foreshadowing of the present.”

It is important to note that Kuhn isn’t saying science textbooks are being irresponsible. If our goal is to inculcate knowledge about the forefront of science as quickly as possible, then brief, cherry-picked histories might very well be the best course of action. However, we shouldn’t mistake the assumption made assumptions for a self-evident truth.

Perhaps most radically, Kuhn claims that once history is taken seriously in this way, it complicates the presumption of scientific progress. Although he doesn’t quite make this distinction explicitly, there are two distinct positions he pushes for:

  1. Methodological: The history of Science shouldn’t antecedently assume progress is always made across time, and should instead investigate whether and what kinds of progress have been made.
  2. Empirical: As a matter of fact, when the history of various scientific disciplines are studied, we find points of discontinuity which make it difficult to believe in straight-forward progress.

The entire text can be seen as an argument that although science does mostly progress, there are occasional revolutions during which straightforward progress is threatened. To understand his argument though, we first need to understand what progress means, and to do that we need to understand his idea of a paradigm.

II. What’s the deal with paradigms?

To understand what paradigms are, I think it makes sense to begin again with why Kuhn invokes it. The answer lies in the fact that the way scientists work today is through highly specialized disciplines and groups, each of which have their own conferences, journals, problems, etc. To try to come to grip with how science works, he treats as his basic units groups working relatively cohesively. But he isn’t interested in these groups sociologically alone, but rather to get a sense of the ideas they share, the “scientific imagination” of the group.

But here’s a problem: methodologically, to characterize a community he will have to rely on the sociological dimension (looking at what textbooks are read, which journals are being published in, etc). But the sociological units are only invoked to characterize ideas supposedly shared, otherwise why choose certain journals and not others?

He is sensitive to this circularity in his Postscript:

The term ‘paradigm’ enters the preceding pages early, and its manner of entry is intrinsically circular. A paradigm is what the members of a scientific community share, and, conversely, a scientific community consists of men who share a paradigm.

While this circularity exists, Kuhn also believes it isn’t a vicious circularity, since the two aspects — the sociological and the ideas — can inform each other. Here’s one way this could happen: you could start by identifying a scientific sub-community through what seem like cohesive patterns of interaction, and then study their ideas closely. This study might reveal that the community is in fact made up of multiple somewhat independent sub-groups, or that its history is quite fragmented. These insights could then lead to a further revision of the initially identified group.

In this manner, taking the idea of a paradigm seriously can potentially help us identify groups small enough to study patterns of interactions in a sustained way, and big enough to understand the relevant group dynamics.

III. Cool, cool, but what’s a paradigm?

I imagine a reader at this juncture going: “It’s all very nice to know that paradigms are attempts to capture something like a shared scientific imagination of a group of people, but what does ‘paradigm’ even mean?”

Here Kuhn again relies on scientific pedagogy or how science is taught (Kuhn himself had a phD in Physics). He points out that although theories and principles are taught in textbooks, they are never taught as abstract sentences to be repeated endlessly. Instead, they are stated and then immediately fleshed out through illustrative examples and back-of the-text problems. Through the solutions provided for exercises, students learn what kind of problems are approachable and what a good solution looks like. Once these are taught, more difficult problems and questions are provided to expand the applicability of what was taught.

It’s this whole bundle that helps inculcate students into a specific discipline, and he calls this a paradigm:

In learning a paradigm the scientist acquires theory, methods, and standards together, usually in an inextricable mixture.

Paradigms historically emerge by being more successful than any alternative, but is by no means a comprehensive description of everything. Instead it is something like an approach, and most scientific work consists in making the paradigm more precise and further “articulating” the paradigm, that is, extending the paradigm to more of nature. This sounds easy, but to “shove” nature into the “boxes” of the paradigm, that is, to successfully use its concepts, methods, instrumental techniques, etc., is incredibly difficult and often required great ingenuity, which can involve the invention of whole mathematical techniques and instruments.

Kuhn suggests that there are three broad kinds of scientific work related to paradigms that occupy most scientists’ time during normal scientific work:

First is that class of facts that the paradigm [determines] both with more precision and in a larger variety of situations.
A second usual but smaller class of [independent] factual determinations is directed to those facts that…can be compared directly with predictions from the paradigm theory.
A third class of experiments and observations …consists of empirical work undertaken to articulate the paradigm theory, resolving some of its residual ambiguities and permitting the solution of problems to which it had previously only drawn attention…Often a paradigm developed for one set of phenomena is ambiguous in its application to other closely related ones. Then experiments are necessary to choose among the alternative ways of applying the paradigm to the new area of interest.

The reason paradigms are perfect for scientific work is because they are detailed and concrete enough to guide work, but there are enough spaces and limitations that scientists have enough to go on.

Paradigms gain their status because they are more successful than their competitors in solving a few problems that the group of practitioners has come to recognize as acute. To be more successful is not, however, to be either completely successful with a single problem or notably successful with any large number. The success of a paradigm-whether Aristotle’s analysis of motion, Ptolemy’s computations of planetary position, Lavoisier’s application of the balance, or Maxwell’s mathematization of the electromagnetic field-is at the start largely a promise of success discoverable in selected and still incomplete examples. Normal science consists in the actualization of that promise, an actualization achieved by extending the knowledge of those facts that the paradigm displays as particularly revealing, by increasing the extent of the match between those facts and the paradigm’s predictions, and by further articulation of the paradigm itself.

This restriction of the scientist’s attention isn’t a bad thing, since it is the shared focus on a narrow set of problems that allows for a range people to collaborate and work out a theory’s details:

By focusing attention upon a small range of relatively esoteric problems, the paradigm forces scientists to investigate some part of nature in a detail and depth that would otherwise be unimaginable…Normal science, the puzzle-solving activity we have just examined, is a highly cumulative enterprise, eminently successful in its aim, the steady extension of the scope and precision of scientific knowledge.

IV. Paradigms as ways of seeing

Importantly, for Kuhn a scientist’s relationship to a paradigm isn’t one of distance and voluntary use. Rather, the paradigm is a way of seeing the world itself. This might seem somewhat strange, but we have to remember that at the forefront of scientific work, you don’t usually have an abundance of options. Existing scientific work is the only guide to what the unknown could be like. This isn’t to say that no imaginative work goes on, but still, hardly anyone comes up with a brand new theory from scratch out of nowhere:

No part of the aim of normal science is to call forth new sorts of phenomena [i.e., unanticipated by the paradigm expectations]; indeed those that will not fit the box are often not seen at all. Nor do scientists normally aim to invent new theories, and they are often intolerant of those invented by others. Instead, normal-scientific research is directed to the articulation of those phenomena and theories that the paradigm already supplies.

This is important because some philosophers idealize a view of science where a theory (or a set of theories) has to make predictions, and then these have to be tested, and if they fail the theory has to be rejected. We can see how this picture makes no sense at all for Kuhn for at least two reasons.

First, scientific work is predicated on major theories having gaps and inaccuracy that needs to be worked out. Of course they are not going to make accurate predictions then, at least in some areas, and so the idea of falsification is highly unhelpful as a guide to any actual scientific practice.

Second, if paradigms are ways of seeing the world, what would testing a paradigm’s theories and their rejection even look like? Would we then retreat into skepticism? Therefore, Kuhn insists, testing a well-lodged theory never happens in isolation, but only in comparison with another theory.

Once it has achieved the status of paradigm, a scientific theory is declared invalid only if an alternate candidate is available to take its place. No process yet disclosed by the historical study of scientific development at all resembles the methodological stereotype of falsification by direct comparison with nature. That remark does not mean that scientists do not reject scientific theories, or that experience and experiment are not essential to the process in which they do so. But it does mean-what will ultimately be a central point-that the act of judgment that leads scientists to reject a previously accepted theory is always based upon more than a comparison of that theory with the world. The decision to reject one paradigm is always simultaneously the decision to accept another, and the judgment leading to that decision involves the comparison of both paradigms with nature and with each other.

But even these comparisons between paradigms and alternative theories do not always happen. If a paradigm is considered healthy and interesting work is being produced based on it, then the mere possibility of an alternative theory doesn’t really capture the attention of scientists. This is because as promising as an alternative might seem, any theory needs to be worked on by a number of people for it to be fleshed out adequately. Therefore, for an alternative to be taken seriously, an existing paradigm will first have to enter a period of crisis.

The restriction of the scientist’s attention by their paradigm, even if good policy for most of the time, obviously can’t hold forever. Nature does surprise us, and so often there are phenomenon that can’t be handled by the paradigm. If extended work cannot deal with it, it is considered an anomaly. Anomalies make scientists start suspecting that their working assumptions might not be adequate to deal with nature, and this opens up the door to a loosening of some assumptions, and the discovery of brand new, previously unthinkable phenomenon.

As anomalies accumulate, the faith in even fundamental assumptions gets shaken, and a period of crisis is entered. During the crisis, scientists are particularly open-minded to change, and if an alternative paradigm candidate makes an appearance and makes some long-standing problem suddenly tractable, a revolution is brought about.

V. Revolution

Because a paradigm is a way of seeing the world, a change to a whole new paradigm is bound to be discontinuous with the old.

The transition from a paradigm in crisis to a new one from which a new tradition of normal science can emerge is far from a cumulative process…Rather it is a reconstruction of the field from new fundamentals, a reconstruction that changes some of the field’s most elementary theoretical generalizations as well as many of its paradigm methods and applications.

There can be changes in what entities are thought to exist, what kinds of problems are worth pursuing, what standards should be followed, etc. Here’s where the distinction I made at the beginning, between the methodological point about simply refraining from assuming progress occurs, and an empirical observation that often there isn’t straightforward progress, becomes important. The actual historical record needs to be consulted to know what continuities exist and don’t.

On one hand, we shouldn’t be too confident that there will always be earlier discoveries carried over and simply re-interpreted. On the other hand, new paradigms never start from scratch. Kuhn insists that there “will be a large but never complete overlap between the problems that can be solved by the old and by the new paradigm” and that with regard to the work performed under normal science, “at least part of that achievement always proves to be permanent”.

The absence of perfect overlap between new and old paradigms complicates but doesn’t do away with a notion of progress. For instance, if we compare two theories, one that was held later than the other, then there will be a clear set of metrics according to which the later paradigm would be indubitably superior:

it should be easy to design a list of criteria that would enable an uncommitted observer to distinguish the earlier from the more recent theory time after time. Among the most useful would be: accuracy of prediction, particularly of quantitative prediction; the balance between esoteric and every· day subject matter; and the number of different problems solved…simplicity, scope, and compatibility with other specialties.

But what will be lost in this more complicated picture, is that ability to specify antecedently, or at the moment of crisis itself, a universally agreed upon and binding criterion for theory choice:

Debates over theory-choice cannot be cast in a form that fully resembles logical or mathematical proof. In the latter, premises and rules of inference are stipulated from the start. If there is disagreement about conclusions, the parties to the ensuing debate can retrace their steps one by one, checking each against prior stipulation. At the end of that process one or the other must concede that he has made a mistake, violated a previously accepted rule. After that concession be has no recourse, and his opponent’s proof is then compelling.

In contrast, scientists who disagree can only hope to convince more and more of their colleagues by showing that it makes better sense to either stick with the old or shift to the new. As the old paradigm continues to languish and the new starting to deliver more and more on its promise, more people will shift and a revolution occurs.

Instead of progress towards a goal, this is a view of science as progressing away from poorer paradigms to better ones, even if somewhat rockily. Although this conclusion is relatively modest, many readers of Kuhn have taken him to be some kind of propagandist for irrationality. For my part, I think a big reason Kuhn didn’t worry too much about whether he was introducing irrationality into the narrative was because as a scientist he had faith in the scientific community as a whole, that they would exercise good judgement even if not all at once. So on the whole, the rationality of science wouldn’t seriously be jeopardized. But of course, that won’t satisfy those who operate under a need for an imagined pure rationality, and so Kuhn is still mistrusted in some circles.

Parting Criticism

Structure is now more than 50 years old, and we are under no obligation to refrain from criticizing it.

As I’ve tried to indicate, Kuhn’s methods are often novel, and there are quite a few assumptions that go into this conclusions. For example, even if a paradigm shapes people’s way of seeing the world, does the paradigm always have to be taken monolithically? As later philosophers would suggest, it does seem more useful to think of certain parts of the paradigm being more central, while others more disposable. There are also probably a lot more theory-neutral observations than Kuhn lets on, and it’s not really clear if paradigms can blind people to them all. If a theory predicted an eclipse, will the mere presence of a different paradigm keep people from seeing the darkening, even if they ultimately interpret it differently?

Kuhn also thinks that because paradigms are distinct ways of seeing the world, communication during a paradigm change is necessarily partial (he does try to downplay this, but it seems half-hearted). But while this may be true for some scientists, it’s also quite clear that most scientists are quite fluent in Newtonian mechanics, even while thinking it is at best an approximation, so it’s not clear to what degree this communication barrier exists. Kuhn does argue at one point that once a paradigm changes, those in the new one cannot see “through” the old one as its true believers did, they can only play at doing so. Well maybe so, but doesn’t seem particularly important. A fascination with gestalt psychology characterizes the book a little too much, in my opinion. And while it is true that paradigms might use the same terms in different ways (eg: “mass”), I don’t think this is as intractable, or at least as important, a problem as he makes it out to be.

There are also stylistic choices which I think are unfortunate (stylistic and not substantive, at least under my reading). Talk of “puzzle solving” does make scientists sound trivial, even if there are good reasons to call it so (ie., they involve both rules and inventiveness). There are also a lot of phrasing which is just misleading — “No part of the aim of normal science is to call forth new sorts of phenomena” makes scientists aren’t engaged in a creative enterprise. And as a scientist who held science is quite high regard, I seriously doubt if Kuhn actually meant to demean the work scientists do.

But what’s unhelpful are bad readings of the book, which seem to proliferate. In my experience, this is because Kuhn is taking his specific background in science and attempting to apply historical analysis to understand its working. He isn’t engaged in metaphysical speculation about the nature of the relationship between science and some “nature” outside it. He isn’t particularly concerned with what what distinguishes science from pseudoscience. He also isn’t interested in an external history of science, where sociological and political conditions of scientific change is studied. And perhaps the avoidance of these is a shortcoming. Still, understanding the book on its own terms is a worthwhile endeavor, and we shouldn’t mistake shoddy readings for profound insight.

Originally published at on August 12, 2018.