Thomas Kuhn's The Structure of Scientific Revolutions was a landmark book in the history of science. Up until its publication, scholars and scientists had generally held to the notion of gradualism, by which they meant that scientific discovery was a process that moved slowly forward and was constantly being reshaped and modified based on the results of an ever-succeeding set of experimental results. Kuhn argued against this line of reasoning, saying that rather than the result of conscious and purposeful scientific experimentation, the most significant discoveries in science happen at the most unexpected moments due to unforeseen circumstances, either in methodology or in scientists’ basic understanding of theory. The result was a sudden and revolutionary “paradigm shift,” or, in other words, a complete rethinking of a particular scientific field of study. These paradigm shifts are the basis of what Kuhn calls scientific breakthroughs.
Kuhn contrasted the occurrence of paradigm shifts with what he called “normal science.” Normal science is a period of relative inactivity in a given field of study where no real significant scientific breakthroughs are made. The reason that science can have such periods of stasis, Kuhn argued, is because most scientists do their work under the assumption of certain principles of thought, which Kuhn called scientific “commitments.” By “commitment,” Kuhn meant general ways of thinking about any kind of scientific subject matter or commonly accepted theoretical axioms that guide scientific work. Most scientists, he maintained, are not trying to upset the established norms of scientific thought, but are rather trying to work within those norms to elucidate certain natural characteristics according to a shared and accepted set of scientific knowledge—the commitments to which he referred. Only when (usually by accident) a scientist deviates from these established norms in an extreme way and when the result produces a revolutionary way to rethink a paradigm are scientists in general willing to cast off older commitments for new ways of doing their work.
Kuhn’s theory of scientific revolutions is mirrored in the thought of his contemporary, Stephen Jay Gould, who forcefully argued against the Darwinian theory of gradualism as an explanation of evolution. Gould, rather, came up with his theory of “punctuated equilibrium,” which claims that organisms do not evolve slowly over time, but rather in explosive bursts that punctuate relatively long periods of stability and changelessness. Both Kuhn and Gould have contributed to a reevaluation of the ways in which scholars think about science as a field of study.