Thomas Kuhn: Paradigm Shift Definition & Examples


  • Thomas Kuhn argued that science does not evolve gradually toward truth.
  • Science has a paradigm that remains constant before going through a paradigm shift when current theories can’t explain some phenomenon, and someone proposes a new theory.
  • A scientific revolution occurs when: (i) the new paradigm better explains the observations and offers a model that is closer to the objective, external reality; and (ii) the new paradigm is incommensurate with the old.
  • For example, Lamarckian evolution was replaced with Darwin’s theory of evolution by natural selection.

Paradigm Shift

Thomas Kuhn attacks “development-by-accumulation” views of science which hold that science progress linearly by accumulating theory-independent facts.  Kuhn looked at the history of science and argued that science does not simply progress by stages based upon neutral observations (e.g., Positivism ).

For Kuhn, the history of science is characterized by revolutions in scientific outlook. Scientists have a worldview or “paradigm.”  A paradigm is a universally recognizable scientific achievement that, for a time, provides model problems and solutions to a community of practitioners.

A paradigm is a basic framework of assumptions, principals and methods from which the members of the community work.

It is a set of norms that tell scientists how to think and behave and although in science, there are rival schools of thought, there is still a single paradigm that all scientists accept uncritically.

Scientists accept the dominant paradigm until anomalies are thrown up.  Scientists then begin to question the basis of the paradigm itself, new theories emerge which challenge the dominant paradigm. Eventually, one of these new theories becomes accepted as the new paradigm.

During different periods of science, certain perspectives held sway over the thinking of researchers.  A particular work may “define the legitimate problems and methods of a research field for succeeding generations of practitioners.”

Kuhn’s Phases of Science

According to Kuhn, knowledge that does not evolve according to the four main phases may not be considered scientific.

paradigm shift cycle

Phase 1: Pre-science

  • The pre-paradigmatic state refers to a period before a scientific
    consensus has been reached.
  • Disorganized and diverse activity.
  • The constant debate over fundamentals.
  • As many theories as there are theorists.
  • No commonly accepted observational basis. The conflicting theories are constituted with their own set of theory-dependent observations.

Phase 2: Normal Science

(most common – science is usually stable)

  • A paradigm is established, which lays the foundations for legitimate work within the discipline. Scientific work then consists of the articulation of the paradigm in solving puzzles that it throws up.
  • A paradigm is a conventional basis for research; it sets a precedent.
  • Puzzles that resist solutions are seen as anomalies.
  • Anomalies are tolerated and do not cause the rejection of the theory, as scientists are confident these anomalies can be explained over time.
  • Scientists spend much of their time in the Model Drift step, battling anomalies that have appeared. They may or may not know this or acknowledge it.
  • It is necessary for normal science to be uncritical. If all scientists were critical of a theory and spent time trying to falsify it, no detailed work would ever get done.

“Normal Science, the activity in which most scientists inevitably spend almost all of their time, is predicated on the assumption that the scientific community knows what the world is like. Much of the success of the enterprise derives from the community’s willingness to defend that assumption, if necessary, at considerable cost. Normal Science, for example, often suppresses fundamental novelties because they are necessarily subversive of its basic commitments” (Kuhn, 1996, p. 5).

Phase 3: Crisis

  • This is where the paradigm shift occurs.
  • Anomalies become serious, and a crisis develops if the anomalies undermine the basic assumptions of the paradigm and attempt to remove them consistently fail.
  • Under these circumstances, the rules for applying the paradigm become relaxed. Ideas that challenge the existing paradigm are developed.
  • In a crisis, there will be ‘extraordinary science’ where there will be several competing theories.
  • If the anomalies can be resolved, the crisis is over, and normal science resumes. If not, there is a scientific revolution that involves a change of paradigm.

Phase 4: Revolution

  • Eventually, a new paradigm will be established, but not because of any logically compelling justification.
  • The reasons for the choice of a paradigm are largely psychological and sociological.
  • The new paradigm better explains the observations and offers a model that is closer to the objective, external reality
  • Different paradigms are held to be incommensurable — the new paradigm cannot be proven or disproven by the rules of the old paradigm, and vice versa.
  • There is no natural measure or scale for ranking different paradigms.

Critical Evaluation

The enormous impact of Thomas Kuhn’s work can be measured in the changes it brought about in the vocabulary of the philosophy of science: besides “paradigm shift”, Kuhn raised the word “paradigm” itself from a term used in certain forms of linguistics to its current
broader meaning.

The frequent use of the phrase “paradigm shift” has made scientists more aware of and, in many cases, more receptive to paradigm changes, so Kuhn’s analysis of the evolution of scientific views has, by itself, influenced that evolution.

For Kuhn, the choice of paradigm was sustained by, but not ultimately determined by, logical processes.  Kuhn believed that it represented the consensus of the community of scientists. Acceptance or rejection of some paradigm is, he argued, a social process as much as a logical process.

This means Kuhn has been accused of being a relativist. Maybe all the theories are equally valid? Why should we believe in today’s science when it might be overturned in the future? Kuhn vigorously rejected this, claiming that scientific revolutions have always led to new, more accurate theories and represent true progress.

Does science make progress through scientific revolutions?  Are later paradigms better than earlier ones? No, Kuhn suggests, they are just different. The scientific revolutions that supplant one paradigm with another do not take us closer to the truth about how the world is.

Successive paradigms are incommensurable. Kuhn says that a later paradigm may be a better instrument for solving puzzles than an earlier one.  But if each paradigm defines its own puzzles, what is a puzzle for one paradigm may be no puzzle at all for

So why is it progressive to replace one paradigm with another which solves puzzles that the earlier paradigm does not even recognize? Kuhn used his incommensurability thesis to disprove the view that paradigm shifts are objective. Truth is relative to the paradigm.

Science does not change its paradigm overnight. Younger scientists take a new paradigm forward. As Kuhn put it, “a new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it.”

Thomas Kuhn showed contemporary philosophers could not ignore the history of science and the social context in which science takes place.  Science is a product of the society in which it is practiced.

Discussion Question: Is psychology a pre-science?

Was there a cognitive revolution from behaviorism that changed methodology and assumptions? Is cognitive psychology a new paradigm?  Hints: It’s still reductionist; input – the output still uses the experimental method.

How to reference this article:


Thomas, K. (1962). The structure of scientific revolutions Chicago: University of Chicago Press.

Olivia Guy-Evans

BSc (Hons), Psychology, MSc, Psychology of Education

Associate Editor for Simply Psychology

Olivia Guy-Evans is a writer and associate editor for Simply Psychology. She has previously worked in healthcare and educational sectors.

Saul Mcleod, PhD

Educator, Researcher

BSc (Hons) Psychology, MRes, PhD, University of Manchester

Saul Mcleod, Ph.D., is a qualified psychology teacher with over 18 years experience of working in further and higher education.