What Is a Paradigm Shift?

This common phrase has a specific meanings in science and philosophy

Marine iguana in Galapagos
Darwin’s theory of evolution by natural selection is an example of a paradigm-theory.

Juergen Ritterbach/Getty Images

You hear the phrase “paradigm shift” all the time, and not just in philosophy. People talk about paradigm shifts in all sorts of areas: medicine, politics, psychology, and sports. But what, exactly, is a paradigm shift? And where does the term come from?

The term “paradigm shift” was coined by the American philosopher Thomas Kuhn (1922- 1996). It is one of the central concepts in his hugely influential work, "The Structure of Scientific Revolutions," published in 1962. To understand what it means, you first have to understand the notion of a paradigm theory.

Paradigm Theory

A paradigm theory is a general theory that helps to provide scientists working in a particular field with their broad theoretical framework—what Kuhn calls their “conceptual scheme.” It provides them with their basic assumptions, key concepts, and methodology. It gives their research its general direction and goals. It represents an exemplary model of good science within a particular discipline.

Examples of Paradigm Theories

  • Ptolemy’s geocentric model of the universe (with the earth at the center)
  • Copernicus’ heliocentric astronomy (with the sun at the center)
  • Aristotle’s physics
  • Galileo's mechanics
  • The medieval theory of the four “humors” in medicine
  • Isaac Newton's theory of gravity
  • John Dalton’s atomic theory
  • Charles Darwin's theory of evolution
  • Albert Einstein’s theory of relativity
  • Quantum mechanics
  • The theory of plate tectonics in geology
  • Germ theory in medicine
  • Gene theory in biology

Paradigm Shift Definition

A paradigm shift occurs when one paradigm theory is replaced by another. Here are some examples:

  • Ptolemy’s astronomy giving way to Copernican astronomy
  • Aristotle’s physics (which held that material objects had essential natures that determined their behavior) giving way to the physics of Galileo and Newton (which viewed the behavior of material objects as being governed by laws of nature).
  • Newtonian physics (which held time and space to be the same everywhere, for all observers) giving way to Einsteinian physics (which holds time and space to be relative to the observer’s frame of reference).

Causes of a Paradigm Shift

Kuhn was interested in the way science makes progress. In his view, science can’t really get going until most of those working within a field agree upon a paradigm. Before this happens, everyone is doing her own thing in her own way, and you can’t have the sort of collaboration and teamwork that is characteristic of professional science today.

Once a paradigm theory is established, those working within it can start doing what Kuhn calls “normal science.” This covers most scientific activity. Normal science is the business of solving specific puzzles, collecting data, and making calculations. Normal science includes:

  • Working out how far each planet in the solar system is from the sun
  • Completing the map of the human genome
  • Establishing the evolutionary descent of a particular species

But every so often in the history of science, normal science throws up anomalies—results that can’t easily be explained within the dominant paradigm. A few puzzling findings by themselves wouldn’t justify ditching a paradigm theory that has been successful. But sometimes the inexplicable results start piling up, and this eventually leads to what Kuhn describes as a “crisis.”

Examples of Crises Leading to Paradigm Shifts

At the end of the 19th century, the inability to detect the ether—an invisible medium posited to explain how light traveled and how gravity operated—eventually led to the theory of relativity.

In the 18th century, the fact that some metals gained mass when burned was at odds with phlogiston theory. This theory held that combustible materials contained phlogiston, a substance that was released through burning. Eventually, the theory was replaced by Antoine Lavoisier’s theory that combustion requires oxygen.

Changes That Occur During a Paradigm Shift

The obvious answer to this question is that what changes is simply the theoretical opinions of scientists working in the field. But Kuhn’s view is more radical and more controversial than that. He argues that the world, or reality, cannot be described independently of the conceptual schemes through which we observe it. Paradigm theories are part of our conceptual schemes. So when a paradigm shift occurs, in some sense the world changes. Or to put it another way, scientists working under different paradigms are studying different worlds.

For example, if Aristotle watched a stone swinging like a pendulum on the end of a rope, he would see the stone trying to reach its natural state: at rest, on the ground. But Newton wouldn’t see this; he’d see a stone obeying the laws of gravity and energy transference. Or to take another example: Before Darwin, anyone comparing a human face and a monkey’s face would be struck by the differences; after Darwin, they would be struck by the similarities.

Science Progresses Through Paradigm Shifts

Kuhn’s claim that in a paradigm shift the reality that is being studied changes is highly controversial. His critics argue that this “non-realist” point of view leads to a sort of relativism, and hence to the conclusion that scientific progress has nothing to do with getting closer to the truth. Kuhn seems to accept this. But he says he still believes in scientific progress since he believes that later theories are usually better than earlier theories in that they are more precise, deliver more powerful predictions, offer fruitful research programs, and are more elegant.

Another consequence of Kuhn’s theory of paradigm shifts is that science does not progress in an even way, gradually accumulating knowledge and deepening its explanations. Rather, disciplines alternate between periods of normal science conducted within a dominant paradigm, and periods of revolutionary science when an emerging crisis requires a new paradigm.

That is what "paradigm shift" originally meant, and what it still means in the philosophy of science. When used outside philosophy, though, it often just means a significant change in theory or practice. So events like the introduction of high definition TVs, or the acceptance of gay marriage, might be described as involving a paradigm shift.