Thomas Kuhn's Theory of Scientific Revolutions
Natural Phenomena, Science, and Philosophy of Science

Kuhn's Model of Scientific Revolutions

Some Philosophical Aspects of Kuhn's Theory

Questions for Study

Natural Phenomena, Science, and Philosophy of Science

Now that we have looked at what is often referred to as the first major scientific revolution in modern history -- the cosmological revolution from Copernicus to Newton -- we will go on to look at philosophies of science that attempt to explain the historical dynamics of scientific revolutions. The process can be conceptualized, in a preliminary and somewhat simplistic way, as a three tiered one:

Natural phenomena exist which we wish to study. (The extent to which natural phenomena exist independently of the observer is a major philosophical problem, especially in philosophy of quantum mechanics. But we will assume a fairly robust degree of independence to start with; this may be modified later as we reflect further).

Natural scientists investigate these natural phenomena and develop theories that make predictions and can be tested against the reality which they attempt to describe, classify, and explain. (Again, a note of caution. It is easy -- and almost any high school textbook does so -- to invoke "the scientific method" as a nearly infallible means by which scientists develop their theories. But this is once again to oversimplify -- much of philosophy of science is devoted to demystifying this simplification, by showing the complex and varying approaches which science has taken to natural phenomena).

Philosophers of science investigate the logical structure of scientific theories and the historical dynamics of their development, modifications, and even replacement (for example: the replacement of the geocentric cosmology with a heliocentric one which we have just examined). Philosophers of science (allied often enough, though not always, with historians of science), are therefore twice removed from the natural phenomena which are the subject matter of science. But at the same time, this "distance" allows them to adopt a more critical approach.

Kuhn's Model of Scientific Revolutions

Perhaps the best known philosopher of science in the last half century is Thomas Kuhn (1922-1996), who was for many years a professor of philosophy and history of science at MIT. Kuhn, who died just a few years ago, held his PhD in physics, but was asked as a young faculty member to teach a course in history of science. He became fascinated with the process by which theories, once held to be true, were replaced by very different ones, also held to be true. For example, the view that all matter was made of Earth, Air, Water and Fire held sway for over two millenia; yet it now seems crude and even child-like in comparison to the modern theory of chemical elements. Nonetheless, it was held to be adequate for a much longer period of time.

For Kuhn, the problem was two-fold: (i) to explain why scientific theories are accepted, and (ii) to explain why scientific theories are replaced. These two aspects are intimately related, and the key concept that Kuhn develops is that of "paradigm" -- a reigning or dominant approach to solving problems in a given area of science.

Kuhn presented his views in Structure of Scientific Revolutions (first edition 1962, second edition 1970). He argued that scientific revolutions proceed through the following stages:

"Normal Science", that is to say everyday, bread-and-butter science, is a "puzzle-solving" activity conducted under a reigning "paradigm".

The paradigm is the example or model of a great scientific achievement (such as Newton's theory of gravity, or Einstein's theory of relativity) which provides an inspiration and a guide showing how to do scientific research. It is not quite an explicit set of rules and regulations (not a recipe or formula), but it does clearly "show the way".

"Puzzle solving" is the normal or everyday activity of scientists, and consists of problems which are believed, in advance, to have a solution, if only enough ingenuity and effort is brought to bear, using the paradigm as a guide.

An "anomaly" arises when a puzzle, considered as important or essential in some way, cannot be solved. The anomaly cannot be written off as just an ill-conceived research project; it continues to assert itself as a thorn in the side of the practicing scientists. The anomaly is a novelty that cannot be written off, and which cannot be solved. Examples of anomalies include:

According to Newtonian mechanics, there should be a difference in the speed of light when it is issued from a moving source. Careful experiments in the late 19th century found no such difference, despite the most accurate of instruments.

According to the Theory of the special creation of species, a divine being created each species separately and individually, perfectly adapted to its environment. The discovery of the fossil remains of species not corresponding to any existing species (extinct species) contradicted this key assumption of biology before Darwin.

This opens up a period called the "crisis", during which time new methods and approaches are permitted, since the older ones have proved incapable of rising to the task at hand (solving the anomaly). Views and procedures previously considered heretical are temporarily permitted, in the hope of cracking the anomaly.

One of these new approaches is successful, and it becomes the new paradigm through a "paradigm shift". This constitutes the core of the scientific revolution.

The new paradigm is popularized in text-books, which serve as the instruction material for the next generation of scientists, who are brought up with the idea that the paradigm -- once new and revolutionary -- is just the way things are done. The novelty of the scientific revolution recedes and disappears, until the process is begun anew with another anomaly-crisis-paradigm shift.

Some Philosophical Aspects of Kuhn's Theory

Kuhn also has made a number of major philosophical claims in the context of developing his model of how science produces revolutions in theory. I mention them here in passing, as just the critical examination of these claims could be the subject of a whole course:

(1) Scientists cannot by themselves "translate" between and old and a new paradigm; these paradigms are "incommensurable", and can be (partially) translated only with the aid of historians and philosophers of science. For example, the explanation for combustion before the oxygen theory invoked a substance, widely accepted in the 18th century, known as "phlogiston", which was given off when a material burned. The modern theory explains the same phenomena as due to the taking-in of oxygen, not the expulsion of the non-existent "phlogiston". A student of chemistry would need a specialist to translate the older theory into modern terms, and even then, aspects of it would remain somewhat mysterious, since taken out of their 18th century context where they made sense.

(2) Scientists escape the dominant paradigm which forms, as it were, their "skin", inside of which they conduct their research. Consequently, there is no "higher authority" who can adjudicate, or decide once and for all, competing truth-claims. All we have are the paradigms of today (the context for on-going research) and those of the past (partially translated by historians and philosophers of science). Not only can there be no absolute truth (true once and for all), but Kuhn makes the more radical claim that the concept of "truth" can be dispensed with entirely, replaced by that of "successful problem solving within a paradigm". Similarly, "objectivity" as a notion independent of the inquiring scientist has no meaning, and is replaced by the methods adopted as standard within the community of scientists.

(3) Kuhn believed, however, that science progresses over time. This is not, however, a question of approaching or achieving "the truth" (see (2) above),. but a matter of solving more problems under the current paradigm than under past ones. (Some old problems drop out as "pseudo-problems" for the new paradigm, but overall, more new problems get solved).

Questions for Study