Lecture 13


Laudan on Kuhn's Theory of Incommensurable Theories

Before the break, we finished our discussion of Kuhn's theory of scientific revolutions by examining his notion of incommensurability between scientific theories. To review, Kuhn claimed that rival paradigms are always incommensurable. Roughly, that means that there is no completely neutral standpoint from which one can judge the relative worth of the two paradigms. As we discussed, incommensurability comes in three basic varieties in Kuhn's SSR:

As I noted then, the first sense of incommensurability is the fundamental one for Kuhn. That is because the paradigm (in the sense of exemplar, a concrete, definitive achievement) defines by example what problems are worth solving and how one should go about solving them. Since this defines the particular sense in which theories are deemed "simple," "explanatory," "accurate," and so one, the paradigm one adopts as definitive determines which standards one uses to judge theories as adequate.

Thus, according to Kuhn one's particular standards or cognitive values are determined by the paradigm one accepts. There is on his view no higher authority to which a scientist can appeal. There are no "deeper" standards to which one can appeal to adjudicate between two paradigms that say that different problems are important; thus, there is no neutral standpoint from which one can decide between the two theories. It is primarily in this sense that theories are "incommensurable" according to Kuhn.

In the next two weeks, we will examine the notion of cognitive values in science in detail, particularly as discussed in Laudan's book Science and Values. (Note that Laudan's book does not deal with ethical values, but with cognitive ones, and particularly with the notion that there is no paradigm-neutral algorithm for adjudicating between different sets of cognitive values.) Laudan's aim: to find a middle ground between the rule-bound view of Carnap and Popper, and the apparent relativism of Kuhn (i.e., his view that standards of theoretical worth are paradigm-relative, and that there is no higher authority to adjudicate between these standards).

Laudan's claim is that both approaches fail to explain some aspect or another of science, and go too far in predicting the degree of disagreement or consensus in science.

On the rule-bound view, there should normally be consensus as long as scientists are rational. To decide between two competing hypotheses, one has only to examine the evidence. Evidence can be inconclusive, but it can never be conclusive in one way for one person and conclusive in another way for another person. (It is this way according to Kuhn, since to a large extent paradigms are "self-justifying.") In any case, it is always apparent how one could proceed in principle to adjudicate between the two hypotheses, even if it is impossible or impractical for us to do so. If there is a neutral algorithm or decision procedure inherent in "the scientific method," then you can see how the degree of consensus that typically exists in science would be easy to explain. On the other hand, it is difficult to explain how there could be disagreement over fundamentals when people have the same body of evidence before them. Historical study does seem to suggest that indeed science is non-cumulative in important respects, i.e., that in scientific revolutions some standards and achievements are lost at the same time that new ones are gained. (Examples: Dalton, Newton).

On the other hand, it is hard to see how Kuhn could explain how consensus arises as quickly as it does in science, given his incommensurability thesis. Indeed, it is difficult to see how Kuhn can explain why consensus arises at all. Some of his explanations leave one cold, e.g., that all the young people adopt the new theory, and that the older people, who remain loyal to the older framework, simply die off. Why shouldn't the younger scientists be as divided as the older scientists? Similarly, arguing that some groups get control of the universities and journals does not explain why the others don't go off and found their own journals. To see this, consider Kuhn's own analogies between scientific revolutions and political revolutions of religious conversions. In these areas of human discourse, there is little consensus and little prospect for consensus. (Indeed, in the fields of philosophy and sociology of science there is little consensus or prospect for consensus, either.) Here we suspect that the groups differ with regard to their basic (political or religious) values, and that since there is no way of adjudicating between these values, the rifts end up persisting. If science is like that, and there is no "proof" but only "conversion" or "persuasion," then why should there ever be the unanimity that arises during periods of normal science, as Kuhn describes it?

To complicate matters, Kuhn often notes that it usually becomes clear to the vast majority of the scientific community that one paradigm is "better" than another. One important achievement leading to the adopting of the new theory is that it solves the anomaly that created a sense of crisis within the old paradigm. Additionally, the new paradigm may include very precise, quantitative methods that yield more accurate predictions, or they may simply be easier to apply or conceptualize. Often, Kuhn claims not that these are not good considerations in favor of adopting the new paradigm, but that they are "insufficient" to force the choice between scientists. In any case, they are not often present in actual historical cases (e.g., he notes that at first Copernican astronomy was not sufficiently more accurate than Ptolemaic astronomy).

When Kuhn talks like this, he sounds very little like the person who propounds radical incommensurability between theories. Instead, the issue at hand seems to be that the empirical evidence simply does not determine logically which theory is correct. This thesis is often called the "underdetermination" thesis. This is much less radical than saying that scientists "live in different worlds" (incommensurability of experience). Instead, we simply have it that empirical evidence does not determine which theory is correct, and that to fill in the gap scientists have to import their own cognitive values, about which they differ. (These may not be supplied by the paradigm, but rather the paradigm is favored because cognitive values differ.)

Laudan thinks that Kuhn shares many assumptions with Popper and Carnap, in particular the view that science (and pursuit of knowledge in general) is hierarchically structured when it comes to justification. That is, we have the following levels of disagreement and resolution.

Level of Disagreement

Level of Resolution







According to Laudan, Kuhn disagrees with Carnap and Popper about whether scientists share the same cognitive values insofar as they are acting professionally (i.e., as scientists rather than individuals). If so, this would provide a way of resolving any dispute. Kuhn says No; Carnap and Popper (in different ways) says Yes. They both seem to agree that differences in cognitive values cannot be resolved. Thus, the reason Kuhn sees paradigms as incommensurable is simply that on his view there is no higher level to appeal to in deciding between the different values inherent in competing paradigms. Next time, we will examine the implications of the hierarchical picture in detail.