The Structure of Scientific Revolutions

Author: Thomas Kuhn
Date: 1962


1   Introduction: A Role for History

Inevitably, however, the aim of [textbooks] is persuasive and pedagogic; a concept of science drawn from them is no more likely to fit the enterprise that produced them than an image of a national culture drawn from a tourist brochure or a language text. This essay attempts to show that we have been misled by them in fundamental ways. Its aim is a sketch of the quite different concept of science that can emerge from the historical record of the research activity itself.

The historian appears to have two main tasks:

Additional research makes it hard to answer questions. Perhaps science does not develop by the accumulation of individual discoveries and inventions.

Simultaneously, the same historians confront growing difficulties in distinguishing the "scientific" component of past observation and belief from what their predecessors had readily labeled "error" and "superstition".

If these out-of-date beliefs are to be called myths, then myths can be produced by the same sorts of methods that lead to scientific knowledge, else if they are to be called science, then science has included beliefs incompatible with the ones we hold today. Historians choose the latter, but that makes it hard to see science as a process of accretion.

Rather than seeking permanent contributions of an older science to our present vantage, they attempt to display the historical integrity of that science in its own time. They ask, for example, not about the relation of Galileo's view to those of modern science, but rather about the relationship between his views and those of his group, i.e., his teachers, contemporaries, and immediate successors in the sciences. Furthermore, they insist upon studying the opinions of that groups and other similar ones from the view point - usually very different from that of moder science - that gives those opinions the maximum internal coherence and the closest possible fit to nature.

2   The Route to Normal Science

"Normal science" means research firmly based upon one or more past scientific achievements, achievements that some particular scientific community acknowledges for a time as supplying the foundation for its further practice.

Science textbooks recount such achievements, illustrate the body of accepted theory, illustrate many of its successful applications, and compare the application with exemplary experiments. Before textbooks, famous classics fulfilled a similar function.

Paradigms share two essential characteristics:

The study of paradigms is what prepares student for membership in the particular scientific community which he will later practice.

There was a time before universal paradigms emerged. (Kuhn uses the example of theories of light.) During that time, there were multiple competing schools of thought that 'derived strength from its relation to some particular metaphysic' emphasizing the phenomena that its own theory could do most to explain. Each of them produced significant contributions from which Newton drew the first nearly uniformly accepted paradigm for physical optics.

Kuhn calls that time immature and notes it is not unfamiliar in creative fields today, nor is it incompatible with significant discovery and invention.

We see this all the time in CS. Religious wars and such.

> For example, did you plan to shoot a film in 35 mm when cheaper digital video would do? A lower-grade material is not necessarily a lower-quality material. As long as the grade of material is appropriate for its intended use, it might still be of high quality. As another example, fast food and gourmet are two grades of restaurant food, but you may find high-quality and low-quality examples of each.

> Yet though all the experiments were electrical and though most of the experimenters read each other’s works, their theories had no more than a family resemblance.3

History suggests the road to a firm research consensus is extraordinarily arduous.

History also suggests some reasons:

What the fluid theory of electricity did for the subgroup that held it, the Franklinian paradigm later did for the entire group of electricians. It suggested which experiments would be worth performing and which, because directed to secondary or to overly complex manifestations of electricity, would not. Only the paradigm did the job far more effectively, partly because the end of interschool debate ended the constant reiteration of fundamentals and partly because the confidence that they were on the right track encouraged scientists to undertake more precise, esoteric, and consuming sorts of work.9 Freed from the concern with any and all electrical phenomena, the united group of electricians could pursue selected phenomena in far more detail, designing much special equipment for the task and employing it more stubbornly and systematically than electricians had ever done before... Both fact collections and theory articulation became highly directed activities. Both fact collection and theory articulation became highly directed activities. The effectiveness and efficiency of electrical research increased accordingly, providing evidence for a societal version of Francis Bacon’s acute methodological dictum: “Truth emerges more readily from error than from confusion.”10

How does the emergence of a paradigm affect the structure of the group that practices the field?

When an individual or group first produces a synthesis able to attract most of the next generation’s practitioners, the older schools gradually disappear. The new paradigm implies a new and more rigid definition of the field. Those unwilling or unable to accommodate their work to it must proceed in isolation or attach themselves to some other group.11 Historically, they have often simply stayed in the departments of philosophy from which so many of the special sciences have been spawned.

As these indications hint, it is sometimes just its reception of a paradigm that transforms a group previously interested merely in the study of nature into a profession or, at least, a discipline. The formation of specialized journals, the foundation of specialists’ societies, and the claim for a special place in the curriculum have usually been associated with a group’s first reception of a single paradigm.

The more rigid definition of the scientific group has other consequences. When the individual scientist can take a paradigm for granted, he need no longer, in his major works, attempt to build his field anew, starting from first principles and justifying the use of each concept introduced. That can be left to the writer of textbooks. Given a textbook, however, the creative scientist can begin his research where it leaves off and thus concentrate exclusively upon the subtlest and most esoteric aspects of the natural phenomena that concern his group. No longer will his researches usually be embodied in books addressed, like Franklin’s Experiments . . . on Electricity or Darwin’s Origin of Species, to anyone who might be interested in the subject matter of the field. Instead they will usually appear as brief articles addressed only to professional colleagues, the men whose knowledge of a shared paradigm can be assumed and who prove to be the only ones able to read the papers addressed to them.

Today in the sciences, books are usually either texts or retrospective reflections upon one aspect or another of the scientific life. The scientist who writes one is more likely to find his professional reputation impaired than enhanced. Only in the earlier, pre-paradigm, stages of the development of the various sciences did the book ordinarily possess the same relation to professional achievement that it still retains in other creative fields.

In dynamics, research became similarly esoteric in the later Middle Ages, and it recaptured general intelligibility only briefly during the early seventeenth century when a new paradigm replaced the one that had guided medieval research.

Ever since prehistoric antiquity one field of study after another has crossed the divide between what the historian might call its prehistory as a science and its history proper. These transitions to maturity have seldom been so sudden or so unequivocal as my necessarily schematic discussion may have implied. But neither have they been historically gradual.

Sometime between 1740 and 1780, electricians were for the first time enabled to take the foundations of their field for granted. From that point they pushed on to more concrete and recondite problems, and increasingly they then reported their results in articles addressed to other electricians rather than in books addressed to the learned world at large. As a group they achieved what had been gained by astronomers in antiquity and by students of motion in the Middle Ages, of physical optics in the late seventeenth century, and of historical geology in the early nineteenth. They had, that is, achieved a paradigm that proved able to guide the whole group’s research. Except with the advantage of hindsight, it is hard to find another criterion that so clearly proclaims a field a science.

3   The Nature of Normal Science

In established usage, a paradigm is an accepted model or pattern.

A successful paradigm is so because:

  1. It is more successful than its competitors in solving a few problems that practitioners recognize as acute
  2. It shows promise of success in selected and incomplete examples (notably,it is not completely successful and leaves many problems open)

During period of normal science, most scientists spend their careers doing "mop-up" work on these new paradigms (as mature sciences leave a lot of mop-up work to do) which mostly involves explaining nature according to the new paradigm. Normal science essentially does not try to come up with counter examples and often ignores them as well as new theres. This seems bad at first, but period of normal science are important to focus research on a small range of esoteric problems in such depth that would otherwise be unimaginable (and never undertaken).

The three foci of normal scientific research are:

  1. Determination of significant fact
  2. Matching of facts with theory
  3. Articulation of theory (filling in details)

On the experimental side (factual scientific investigation), these three include:

On the theoretical side, these three include:

# 04. Normal Science as Puzzle-Solving

If the aim of normal science is not major substantive novelties then why are these problems undertaken at all?

  1. To scientists at least, the result gained in normal research are significant because they add to the scope and precision with which the paradigm can be applied.
  2. Though its outcome can be anticipated, often so well that the actual result is uninteresting, the way to achieve that outcome remains very much in doubt. The man who succeeds proves himself an expert puzzle-solver.

Puzzles are, as the standard definition, that special category of problems that can serve to test ingenuity or skill in solution. It is no criterion of goodness in a puzzle that its outcome be intrinsically interesting or important. On the other hand, assured existence of a solution is.

One of the things a scientific community acquires with a paradigm is a criterion for choosing problems that can be assumed to have solutions. To a great extent these are the only problems that the community will admit as scientific or encourage its members to undertake. Other problems, including many that had previously been standard, are rejected as metaphysical or too problematic to be worth the time. A paradigm in that matter can insulate that community from important problems that not reducible to puzzle form because they cannot be stated in terms of conceptual and instrumental tools the paradigm supplies. Such problems can be a distraction. One of the reasons why normal science seems to progress so rapidly is that its practitioners concentrate on problems that only their own lack of ingenuity should keep them from solving.

A scientists motivation is to succeed in solving a puzzle that no one before has solved or solved so well.

A puzzle has an assured solution, rule that limit both the nature of acceptable solutions and the steps by which they are to be obtained. If we can accept a considerably broadened use of the term 'rule' (one that will occasionally equate it with 'established viewpoint' or with 'preconception') then the problems accessible within a given research tradition display something much like this set of puzzle characteristics.

One of the rules is validity. Do measuring tools measure what they purport to measure? Until they can be shown to, they cannot be used to solve problems.

> The man who builds an instrument to determine optical wave lengths must not be satisfied with a piece of equipment that merely attributes particular numbers to particular spectral lines. He is not just an explorer or measurer. On the contrary, he must show, by analyzing his apparatus in terms of the established body of optical theory, that the numbers hi instrument produces are the one that enter theory as wave lengths. If some residual vagueness in the theory or some unanalyzed component of his apparatus prevents his completing that demonstration, his colleagues may well conclude that he has measured nothing at all. Before they became measures of anything, they had to be related to a theory that predicted the wave-like behavior of matter in motion. - Kuhn, Chapter 4

# 05. The Priority of Paradigms # 06. Anomaly and the Emergence of Scientific Discoveries # 07. Crisis and the Emergence of Scientific Theories # 08. The Response to Crisis # 09. The Nature and Necessity of Scientific Revolutions # 10. Revolutions as Changes of World View # 11. The Invisibility of Revolutions # 12. The Resolution of Revolutions # 12. Progress Through Revolution