Falsification, anomaly, and crisis

In my last post I discussed Karl Popper’s critical rationalism as illustrated by his interpretation of the ancient cosmological debate between Thales and Anaximander. Meanwhile I’ve been reading Thomas Kuhn’s classic 1962 work The Structure of Scientific Revolutions, which offers a rather different picture of the evolution of scientific theory. Near the end of the book Kuhn contrasts Popper’s view with his own, and raises the following objection [1]:

A very different approach to this whole network of problems has been developed by Karl R. Popper who denies the existence of any verification procedures at all. Instead, he emphasizes the importance of falsification, i.e., of the test that, because its outcome is negative, necessitates the rejection of an established theory. Clearly, the role thus attributed to falsification is much like the one this essay assigns to anomalous experiences, i.e., to experiences that, by evoking crisis, prepare the way for a new theory. Nevertheless, anomalous experiences may not be identified with falsifying ones. Indeed, I doubt that the latter exist. As has repeatedly been emphasized before, no theory ever solves all the puzzles with which it is confronted at a given time; nor are the solutions already achieved often perfect. On the contrary, it is just the incompleteness and imperfection of the existing data-theory fit that, at any time, define many of the puzzles that characterize normal science. If any and every failure to fit were ground for theory rejection, all theories ought to be rejected at all times. On the other hand, if only severe failures to fit justifies theory rejection, then the Popperians will require some criterion of “improbability” or of “degree of falsification.” In developing one they will almost certainly encounter the same network of difficulties that has haunted the advocates of the various probabilistic verification theories.

Popper emphasised falsification on the grounds that it provided a way around David Hume’s problem of induction. His insight can be illustrated by noting the asymmetry involved in justifying and refuting universal claims such as “all sheep are white”. If I believe this statement true, I could attempt to verify it by gathering observations of white sheep. But various probabilistic problems emerge as soon as it is wondered how many white sheep I will have to observe before I become justified in believing that all sheep are white. On the other hand, if I deny that all sheep are white all I will need to do to be justified is observe (e.g.) a single black sheep. Popper saw that since scientific hypotheses typically aim at generality, and so take the form of universal claims, a move that exploits this asymmetry can be made. If we view scientific theory not as requiring positive vindication by observation, but as a set of always-provisional conjectures whose acceptance depends on their robustness under attempts at refutation, then Hume’s problem can be dodged.

But as Kuhn notes, this account relies on one-off falsification events acting as conclusive refutations. If they don’t then judgements need to be made about the degree to which a theory is falsified by a given observation, which simply reintroduces all the probabilistic problems that the Popperian move was supposed to avoid. But if they do then every scientific theory ever conceived has already been definitively refuted, because there are always observations that are inconsistent with any given theory. For Kuhn as with Popper these inconsistencies prove to be critical, though not just in how they help to precipitate theory change, but also for the pivotal role they play in setting the agenda for scientific research in a particular field.

The notion most famously associated with Kuhn is that of a scientific ‘paradigm’. A paradigm is something more than a theory — it is what a theory becomes when it is universally or near-universally accepted by a scientific community, to the extent that it can no longer be thought of as answering a set of prior questions but rather as posing the questions to be tackled by the community. The space of all possible scientific problems is just too vast to be approached systematically, and so according to Kuhn a paradigm functions by identifying and isolating a small domain of relevant mysteries. This is why Kuhn sees it as not only unproblematic, but vital to scientific progress that observations which contradict the incumbent paradigm exist. Without them science would be akin to a random search through the Library of Babel, and equally as hopeless. Solving the problems posed by the current paradigm thus becomes the primary task of what Kuhn refers to as ‘normal science’.

Clearly, on Kuhn’s account observations inconsistent with the paradigm cannot be seen as falsifying it. In fact the working assumption of normal science is (indeed must be) that such inconsistencies can be assimilated by the paradigm. The task of normal science is to develop the resources to do so: creating new mathematical techniques to better articulate the theories which constitute the paradigm, working through more and more of its implications, improving the quality and quantity of observational data, building more elaborate technology to enable this, and so on. But sometimes an inconsistency will persist despite the efforts of normal science, and at this point it ceases to be a mystery and takes on the status of an ‘anomaly’. If the anomaly continues to persist despite the increasing resources directed at it by the scientific community then it may provoke members of the community to start questioning the foundational principles of the paradigm itself. At this point the field can be said to be in crisis. For Kuhn this is where normal science ends and ‘extraordinary science’ begins.

With its paradigm in tatters a field may become increasing fragmented, until in the end there are as many competing theories as there are experts, each trying to reconstruct the entire field from the ground up. At some point one of the competing theories will begin to dominate, ultimately becoming established as the new paradigm. The factors involved in the acceptance of the new paradigm may be varied — they will likely involve its ability to deal with the anomaly which led to crisis in the first place along with its successful interpretation of previous experimental results, as well, perhaps, of its ability to meet certain extra-scientific pressures (such as aesthetic standards). But one thing is sure: the new paradigm will come with its own set of mysteries, inconsistencies, and unexplained phenomena. Far from refuting the paradigm before it has even left the ground, these serve to define a new problem space, and in doing so to set the course for the next phase of normal science.

Notes:

1. Thomas S. Kuhn – The Structure of Scientific Revolutions (50th Anniversary Edition) pp.145-146