Are There Revolutions in Science?
In his speculations on scientific development in the original (1962) version of The Structure of Scientific Revolutions (SSR), Thomas Kuhn seems to reject the idea of scientific progress entirely, claiming that scientific theories form part of fixed, independent ‘paradigms’ which lack a common basis of comparison.
What exactly are these paradigms, and how do they relate to scientific revolutions?
First, let’s talk about the different phases of scientific development as outlined by Kuhn.
One of the central features of Kuhn’s model of scientific development is his notion of alternating phases of ‘normal science’ and revolutionary change. According to Kuhn, ‘normal science’ is focused on developing solutions to “puzzles” and engaging in problem-solving activities. This activity — problem-solving — is what Kuhn claims scientists “are trained to do and what… they spend most of their professional lives doing” ¹.
In normal science, he claims, scientists primarily function to engage in problem-solving activities, to arrive at problem-solutions to the particular problems in question.
Although the development of normal science is seen as progressing, with homogeneity present over problem-solving activities, the realist notion that scientific theories related to the truth are not, he emphasizes, a coherent idea. This is because scientific development in the revolutionary phase does not resemble the linear progression of truth associated with a secure foundation of truth, but involves a revision and consequent change of prevailing scientific belief and/or practice².
The sphere of meaning from which scientists assign statements truth-values is embedded in a ‘lexicon’ — a linguistic body of scientific expression — that derives meaning from the paradigm in which the lexis is used³.
Kuhn states that the theories, methods, assumptions, and values that enable scientific research form the basis of what he calls a ‘disciplinary matrix’. These shared theoretical beliefs and research agendas, characterized by a model of problem-solving, is what Kuhn describes as a ‘paradigm’⁴.
A paradigm is governed by a core theory supported by a collection of auxiliary hypotheses. The core theory remains unchanged over the course of a paradigm, while the auxiliary hypotheses are modified in light of incompatible anomalous data.
This modification eventually cannot bear the weight of mounting anomalous data, at which point the leading theory is abandoned or radically altered, thus starting the second phase of revolutionary change.
After this radical paradigm shift, Kuhn claims, the succeeding paradigm and its period of normal science “is not only incompatible but often actually incommensurable with that which has gone before”⁵.
‘Incommensurable’, Kuhn claims, refers to the observation that with no semantic or methodological similarities in form, alternative paradigms have no fixed norms or standards against which they can both be translated. It is impossible to make either a comparative assessment against or show progress between these paradigms.
Kuhn responded to this problem by introducing five values (his criteria) for theory choice, which can be used across paradigms.
Kuhn’s five criteria for theory choice, namely: accuracy, consistency, scope, simplicity, and fruitfulness. According to Kuhn, these values form the rational basis of theory appraisal both within and between paradigms. This proposed criteria for theory evaluation is relatively uncontroversial. But it has several limitations regarding theory choice. For instance, issues with the subjective application, the ambiguity of values, weighting individual interpretations, and paradigm-dependent theory appraisal. Let us briefly consider the first three.
The first limitation is that there is a significant aspect of subjectivity involved when using Kuhn’s criteria for theory choice since the application of the values on which the criteria are based is likely to differ between scientists.
The tension between emphasizing subjectivity and stressing the shared values within a paradigm is not resolved, since it is, of course, the application of these standards and the entailing divergence of judgments between scientists from which the subjectivity is derived.
The second and third limitations essentially follow from the first. According to the second limitation, because Kuhn’s criteria are open to many interpretations there is a large sense in which scientists will use it differently, and so unlike the comparison of (say) unequivocal truth-values Kuhn’s theory comparison bears an explicit ambiguity.
Clearly, Kuhn knows that the values that make up his criteria are open to over one interpretation. This equivocal nature, perhaps, is even more common between competing paradigms, since the likely variation in the analysis and weighting of the values between competing paradigms might increase because of the paradigm’s differing programs of scientific research.
Whether true, the fact remains that the subjective component in the application of the shared values points to enduring incommensurability in Kuhn’s later work.
The general point of the limitations is to say that because the values of Kuhn’s criteria may conflict — simplicity of theories over the accuracy, fruitfulness over scope, etc. — and because understanding the meanings of the five values is implicitly subjective, the criteria appear insufficient to establish which approach should be taken when engaging in science.
Therefore, they fail to uniquely establish what determines the best course of action when evaluating competing scientific theories within particular paradigms. If this is correct under Kuhn’s characterization of theory choice, there would seem to be little-to-no rationality controlling the relation between the criteria of theory choice and the choice verdict (i.e. determination of choice).
Despite these limitations, one thing is clear: Kuhn’s account of scientific development is unique and insightful. Whether there are periodic revolutions or “paradigm shifts” in science is an open question, but the idea itself helps us to question the true nature of scientific development and inquiry.
[1, 2, 3, 4, 5] Kuhn, T., (1969) The Structure of Scientific Revolutions, Chicago: University of Chicago Press.