Incommensurability in Science

More than 50 years after the publication of Thomas Kuhn’s seminal book, The Structure of Scientific Revolutions, this volume assesses the adequacy of the Kuhnian model in explaining certain aspects of science, particularly the social and epistemic aspects of science. One argument put forward is that there are no good reasons to accept Kuhn’s incommensurability thesis, according to which scientific revolutions involve the replacement of theories with conceptually incompatible ones. Perhaps, therefore, it is time for another “decisive transformation in the (...) image of science by which we are now possessed.” Only this time, the image of science that needs to be transformed is the Kuhnian one. Does the Kuhnian image of science provide an adequate model of scientific practice? If we abandon the Kuhnian picture of revolutionary change and incommensurability, what consequences would follow from that vis-à-vis our understanding of scientific knowledge as a social endeavour? -/- The essays in this collection continue this debate, offering a critical examination of the arguments for and against the Kuhnian image of science as well as their implications for our understanding of science as a social and epistemic enterprise. (shrink)

In their reviews of The Kuhnian Image of Science: Time for a Decisive Transformation? (2018), both Markus Arnold (2018) and Amanda Bryant (2018) complain that the contributors who criticize Kuhn’s theory of scientific change have misconstrued his philosophy of science and they praise those who seek to defend the Kuhnian image of science. In what follows, then, I would like to address their claims about misconstruing Kuhn’s theory of scientific change. But my focus here, as in the book, will be (...) the evidence (or lack thereof) for the Kuhnian image of science. I will begin with Arnold’s review and then move on to Bryant’s review. (shrink)

Moti Mizrahi has argued that Thomas Kuhn does not have a good argument for the incommensurability of successive scientific paradigms. With Rouse, Andersen, and others, I defend a view on which Kuhn primarily was trying to explain scientific practice in Structure. Kuhn, like Hilary Putnam, incorporated sociological and psychological methods into his history of science. On Kuhn’s account, the education and initiation of scientists into a research tradition is a key element in scientific training and in his explanation of incommensurability (...) between research paradigms. The first part of this paper will explain and defend my reading of Kuhn. The second part will probe the extent to which Kuhn’s account can be supported, and the extent to which it rests on shaky premises. That investigation will center on Moti Mizrahi’s project, which aims to transform the Kuhnian account of science and of its history. While I do defend a modified kind of incommensurability, I agree that the strongest version of Kuhn’s account is steadfastly local and focused on the practice of science. (shrink)

The aim of this chapter is to explore the relationship between Kuhn’s views about science and scientific realism. I present an overview of key features of Kuhn’s model of scientific change. The model suggests a relativistic approach to the methods of science. I bring out a conflict between this relativistic approach and a realist approach to the norms of method. I next consider the question of progress and truth. Kuhn’s model is a problem-solving model that proceeds by way of puzzles (...) and anomalies rather than progress toward truth. I explore Kuhn’s views about scientific progress in connection with scientific realist views about truth and progress. This leads to consideration of Kuhn’s views about the incommensurability of paradigms, as well as brief consideration of an anti-realist interpretation of his talk of world-change. I conclude by indicating that the scientific realist may endorse some aspects of Kuhn’s view. (shrink)

In his late years, Thomas Kuhn became interested in the process of scientific specialization, which does not seem to possess the destructive element that is characteristic of scientific revolutions. It therefore makes sense to investigate whether and how Kuhn’s insights about specialization are consistent with, and actually fit, his model of scientific progress through revolutions. In this paper, I argue that the transition toward a new specialty corresponds to a revolutionary change for the group of scientists involved in such a (...) transition. I will clarify the role of the scientific community in revolutionary changes and characterize the incommensurability across specialties as possessing both semantic and methodological aspects. The discussion of the discovery of the structure of DNA will serve both as an illustration of my main argument and as reply to one criticism raised against Kuhn—namely, that his model cannot capture cases of revolutionary yet non-disruptive episodes of scientific progress. Revisiting Kuhn’s ideas on specialization will shed new light on some often overlooked features of scientific change. (shrink)

Comparative philosophy between two disparate cultural-philosophic traditions, such as Western and Chinese philosophy, has become a new trend of philosophical fashion in the late twentieth and early twenty-first centuries. Having learned from the past, contemporary comparative philosophers cautiously safeguard their comparative studies against two potential pitfalls, namely cultural universalism and cultural relativism. The Orientalism that assumed the superiority of the Occidental has become a memory of the past. The historical pendulum has apparently swung to the other extreme. The more recent (...) "reverse Orientalism" has started to reclaim the superiority of the Oriental. We have even been told that the twenty-first... (shrink)

The aim of this article is to discuss the relation between indigenous and scientific kinds on the basis of contemporary ethnobiological research. I argue that ethnobiological accounts of taxonomic convergence-divergence patters challenge common philosophical models of the relation between folk concepts and natural kinds. Furthermore, I outline a positive model of taxonomic convergence-divergence patterns that is based on Slater's [2014] notion of “stable property clusters” and Franklin-Hall's [2014] discussion of natural kinds as “categorical bottlenecks.” Finally, I argue that this model (...) is not only helpful for understanding the relation between indigenous and scientific kinds but also makes substantial contributions to contemporary debates about natural kinds.to contemporary debates about natural kinds. (shrink)

Incommensurability may be regarded as driving specialisation, on the one hand, and as posing some problems to interdisciplinarity, on the other hand. It may be argued, however, that incommensurability plays no role in either specialisation or interdisciplinarity. Scientific specialties could be defined as simply 'different' (that is, about different things), rather than 'incommensurable' (that is, competing for the explanation of the same phenomena). Interdisciplinarity could be viewed as the co- ordinated effort of scientists possessing complemetary and interlocking skills, and not (...) as the overcoming of some sort of incommensurable divide. This article provides a comprehensive evaluative examination of the relations between specialisation, interdisciplinarity, and incommensurability. Its aim is to defend the relevance of incommensurability to both specialisation and interdisciplinarity. At the same time, it aims at correcting the tendency, common among many philosophers, to regard incommensurability in a restrictive manner - such as, for example, as an almost purely semantic issue. (shrink)

The paper briefly reviews the main formulations of the incommensurability thesis by Feyerabend and Kuhn, as well as the main criticisms leveled against it. The question is then raised of whether there is a "phenomenon" of incommensurability that has been "discovered". It is argued that there is no such phenomenon.

Attempting to compare scientific theories requires a philosophical model of meaning. Yet different scientific theories have at times—particularly in early chemistry—pre-supposed disparate theories of meaning. When two theories of meaning are incommensurable, we must say that the scientific theories that rely upon them are meta-incommensurable. Meta- incommensurability is a more profound sceptical threat to science since, unlike first-order incommensurability, it implies complete incomparability.

Social studies of science have often treated natural field sites as extensions of the laboratory. But this overlooks the unique specificities of field sites. While lab sites are usually private spaces with carefully controlled borders, field sites are more typically public spaces with fluid boundaries and diverse inhabitants. Field scientists must therefore often adapt their work to the demands and interests of local agents. I propose to address the difference between lab and field in sociological terms, as a difference in (...) style. A field style treats epistemic alterity as a resource rather than an obstacle for objective knowledge production. A sociological stylistics of the field should thus explain how objective science can co-exist with radical conceptual difference. I discuss examples from the Canadian North, focussing on collaborations between state wildlife biologists and managers, on the one hand, and local Aboriginal Elders and hunters, on the other. I argue that a sociological stylistics of the field can help us to better understand how radically diverse agents may collaborate across cultures in the successful production of reliable natural knowledge. (shrink)

I reply to James Marcum’s “What’s the Support for Kuhn’s Incommensurability Thesis? A Response to Mizrahi and Patton”.

In this paper, I argue that there is neither valid deductive support nor strong inductive support for Kuhn’s incommensurability thesis. There is no valid deductive support for Kuhn’s incommensurability thesis because, from the fact that the reference of the same kind terms changes or discontinues from one theoretical framework to another, it does not necessarily follow that these two theoretical frameworks are taxonomically incommensurable. There is no strong inductive support for Kuhn’s incommensurability thesis, since there are rebutting defeaters against it (...) in the form of episodes from the history of science that do not exhibit discontinuity and replacement, as Kuhn’s incommensurability thesis predicts, but rather continuity and supplementation. If this is correct, then there are no compelling epistemic reasons to believe that Kuhn’s incommensurability thesis is true or probable. (shrink)

Scientists working within a paradigm must play by the rules of the game of that paradigm in solving problems, and that is why incommensurability arises when the rules of the game change. If we deny the thesis of the priority of paradigms, then there is no good argument for the incommensurability of theories and thus for taxonomic incommensurability, because there is no invariant way to determine the set of results provable, puzzles solvable, and propositions cogently formulable under a given paradigm.

This is a collection of my essays in the philosophy of science which have been translated into Spanish.

Epistemic relativists often appeal to an epistemic incommensurability thesis. One notable example is the position advanced by Wittgenstein in On certainty (1969). However, Ian Hacking’s radical denial of the possibility of objective epistemic reasons for belief poses, we suggest, an even more forceful challenge to mainstream meta-epistemology. Our central objective will be to develop a novel strategy for defusing Hacking’s line of argument. Specifically, we show that the epistemic incommensurability thesis can be resisted even if we grant the very insights (...) that lead Hacking to claim that epistemic reasons are always relative to a style of reasoning. Surprisingly, the key to defusing the argument is to be found in recent mainstream work on the epistemic state of objectual understanding. (shrink)

Incommensurability was Kuhn’s worst mistake. If it is to be found anywhere in science, it would be in physics. But revolutions in theoretical physics all embody theoretical unification. Far from obliterating the idea that there is a persisting theoretical idea in physics, revolutions do just the opposite: they all actually exemplify the persisting idea of underlying unity. Furthermore, persistent acceptance of unifying theories in physics when empirically more successful disunified rivals can always be concocted means that physics makes a persistent (...) implicit assumption concerning unity. To put it in Kuhnian terms, underlying unity is a paradigm for paradigms. We need a conception of science which represents problematic assumptions concerning the physical comprehensibility and knowability of the universe in the form of a hierarchy, these assumptions becoming less and less substantial and more and more such that their truth is required for science, or the pursuit of knowledge, to be possible at all, as one goes up the hierarchy. This hierarchical conception of science has important Kuhnian features, but also differs dramatically from the view Kuhn expounds in his The Structure of Scientific Revolutions. In this paper, I compare and contrast these two views in a much more detailed way than has been done hitherto. I show how the hierarchical view can be construed to emerge from Kuhn’s view as it is modified to overcome objections. I argue that the hierarchical conception of science is to be preferred to Kuhn’s view. (shrink)

Several recent works in history and philosophy of science have re-evaluated the alleged opposition between the theses put forth by logical empiricists such as Carnap and the so-called "post-positivists", such as Kuhn. Although the latter came to be viewed as having seriously challenged the logical positivist views of science, recent authors (e.g., Friedman, Reisch, Earman, Irzik and Grünberg) maintain that some of the most notable theses of the Kuhnian view of science have striking similarities with some aspects of Carnap's philosophy. (...) Against that reading, Oliveira and Psillos argue that within Carnap's philosophy there is no place for the Kuhnian theses of incommensurability, holism, and theory-ladenness of observations. This paper presents each of those readings and argues that Carnap and Kuhn have non-opposing views on holism, incommensurability, the theory-ladenness of observations, and scientific revolutions. We note at the very end - without dwelling on the point, however - that they come apart on other matters, such as their views on metaphysics and on the context of discovery/justification distinction. (shrink)

One of the objections against the thesis of underdetermination of theories by observations is that it is unintelligible. Any two empirically equivalent theories — so the argument goes—are in principle intertranslatable, hence cannot count as rivals in any non-trivial sense. Against that objection, this paper shows that empirically equivalent theories may contain theoretical sentences that are not intertranslatable. Examples are drawn from a related discussion about incommensurability that shows that theoretical non-intertranslatability is possible.

In this paper I analyze the difficult question of the truth of mature scientific theories by tackling the problem of the truth of laws. After introducing the main philosophical positions in the field of scientific realism, I discuss and then counter the two main arguments against realism, namely the pessimistic metainduction and the abstract and idealized character of scientific laws. I conclude by defending the view that well-confirmed physical theories are true only relatively to certain values of the variables that (...) appear in the laws. (shrink)

At first glance there seem to be many similarities between Thomas S. Kuhn’s and Ludwik Fleck’s accounts of the development of scientific knowledge. Notably, both pay attention to the role played by the scientific community in the development of scientific knowledge. But putting first impressions aside, one can criticise some philosophers for being too hasty in their attempt to find supposed similarities in the works of the two men. Having acknowledged that Fleck anticipated some of Kuhn’s later theses, there seems (...) to be a temptation in more recent research to equate both theories in important respects. Because of this approach, one has to deal with the problem of comparing the most notable technical terms of both philosophers, namely ‘‘thought style’’ and ‘‘paradigm’’. This paper aims at a more thorough comparison between Ludwik Fleck’s concept of thought style and Thomas Kuhn’s concept of paradigm. Although some philosophers suggest that these two concepts are essentially equal in content, a closer examination reveals that this is not the case. This thesis of inequality will be defended in detail, also taking into account some of the alleged similarities which may be responsible for losing sight of the differences between these theories. (shrink)

The paper explores the relativistic implications of the thesis of incommensurability. A semantic form of incommensurability due to semantic variation between theories is distinguished from a methodological form due to variation in methodological standards between theories. Two responses to the thesis of semantic incommensurability are dealt with: the first challenges the idea of untranslatability to which semantic incommensurability gives rise; the second holds that relations of referential continuity eliminate semantic incommensurability. It is then argued that methodological incommensurability poses little risk (...) to the rationality or objectivity of science. For rational theory choice need neither be dictated by an algorithm nor governed by a binding set of rules. The upshot of the discussion is deflationary. There is little prospect for a relativistic conception of science based on inflated claims about the incommensurability of scientific theories. (shrink)

This is a comment on Lena Soler's 'The Incommensurability of Experimental Practices'.

Scientific realism is the position that the aim of science is to advance on truth and increase knowledge about observable and unobservable aspects of the mind-independent world which we inhabit. This book articulates and defends that position. In presenting a clear formulation and addressing the major arguments for scientific realism Sankey appeals to philosophers beyond the community of, typically Anglo-American, analytic philosophers of science to appreciate and understand the doctrine. The book emphasizes the epistemological aspects of scientific realism and contains (...) an original solution to the problem of induction that rests on an appeal to the principle of uniformity of nature. (shrink)

Against the received translation-failure interpretation, this book presents a presuppositional interpretation of incommensurability, that is, the thesis of incommensurability as cross-language communication breakdown due to the incompatible metaphysical presuppositions underlying two competing presuppositional languages, such as scientific languages. This semantically sound, epistemologically well-established, and metaphysically profound interpretation not only affirms the tenability of the notion of incommensurability and confirms the reality of the phenomenon of incommensurability, but also makes some significant contributions to the discussion of many related issues, such as (...) the notion of conceptual schemes, the notion of truth-value status and truth-value conditions, and the issue of cross-language understanding and communication. (shrink)

This is a short introductory discussion of the idea of incommensurability as it is used in the philosophy of science.

This paper strengthens and defends the pluralistic implications of Einstein's successful, quantitative predictions of Brownian motion for a philosophical dispute about the nature of scientific advance that began between two prominent philosophers of science in the second half of the twentieth century (Thomas Kuhn and Paul Feyerabend). Kuhn promoted a monistic phase-model of scientific advance, according to which a paradigm driven `normal science' gives rise to its own anomalies, which then lead to a crisis and eventually a scientific revolution. Feyerabend (...) stressed the importance of pluralism for scientific progress. He rejected Kuhn's model arguing that it fails to recognize the role that alternative theories can play in identifying exactly which phenomena are anomalous in the first place. On Feyerabend's account, Einstein's predictions allow for a crucial experiment between two incommensurable theories, and are an example of an anomaly that could refute the reigning paradigm only after the development of a competitor. Using Kuhn's specification of a disciplinary matrix to illustrate the incommensurability between the two paradigms, we examine the different research strategies available in this peculiar case. On the basis of our reconstruction, we conclude by rebutting some critics of Feyerabend's argument. (shrink)

摘要：通常所接受对库恩有关不可通约性的分类学解释的理解建立在不可译性概念之上，因而是相当不完善的。为了弥补此不足，本文在分类之逻辑语义理论 (a logical-semantic theory of taxonomy)、真值语义理论 (a semantic theory of truth-value)，以及跨语言交流的真值条件理论 (a truth-value conditional theory of cross-language communication) 之基础上，对库恩有关不可通约性的分类学解释进行了重建。根据这种重建，如果两个科学语言具有不相匹配的分类结构，则当一科学语言的核心语句在其所属语境中具有真值、而在另一科学语言之语境中考虑缺乏真值时，这两 种科学语言乃不可通约。通过这种重建，库恩对于不可通约性的成熟解释并非基于保真 (truth-preserving) 可译性或不可译性的概念，而是基于保留真值状态 (truth-value-preserving) 的跨语言交流概念之上。这种重建使得库恩有关不可通约性的解释更具坚实的理论基础、也在概念上更加完整。.

Kuhn's alleged taxonomic interpretation of incommensurability is grounded on an ill defined notion of untranslatability and is hence radically incomplete. To supplement it, I reconstruct Kuhn's taxonomic interpretation on the basis of a logical-semantic theory of taxonomy, a semantic theory of truth-value, and a truth-value conditional theory of cross-language communication. According to the reconstruction, two scientific languages are incommensurable when core sentences of one language, which have truth values when considered within its own context, lack truth values when considered within (...) the context of the other due to the unmatchable taxonomic structures underlying them. So constructed, Kuhn's mature interpretation of incommensurability does not depend upon the notion of truth-preserving translatability, but rather depends on the notion of truth-value-status-preserving cross-language communication. The reconstruction makes Kuhn's notion of incommensurability a well grounded, tenable and integrated notion.Author Keywords: Incommensurability; Thomas Kuhn; Taxonomic structures; Lexicons; Truth-value; Untranslatability; Cross-language communication. (shrink)

Opening remarks delivered at "Incommensurability (and related matters)" conference, Hanover, June 1999.

Philosophers and historians of science have made the claim that successive scientific theories are incommensurable, that is, that many or all of their concepts fail to coincide. This claim has been echoed by cognitive psychologists who have applied it to the successive conceptual schemes of young children, or of children and adults. This paper examines the psychological evidence for the claim and proposes ways of reinterpreting it which do not involve imputing incommensurability. An alternative approach to understanding conceptual change is (...) suggested, according to which novel concepts are introduced against a background of shared concepts, rather than as part of incommensurable conceptual schemes. (shrink)

There are many ways of construing the claim that some categories are more “natural" than others. One can ask whether a system of categories is innate or acquired by learning, whether it pertains to a natural phenomenon or to a social institution, whether it is lexicalized in natural language or requires a compound linguistic expression. This renders suspect any univocal answer to this question in any particular case. Yet another question one can ask, which some authors take to have a (...) bearing on the issue of the naturalness of categories, is whether a system of categories constitutes a unique way of organizing a particular set of entities or phenomena, or whether there are other legitimate classification schemes that can coexist with it. Another way of putting this is by asking whether systems of categories can cut across one another, and if so, under what circumstances. Some philosophers have claimed that crosscutting systems of categories cannot exist as genuine natural kinds. This paper examines that claim and puts forward some counterexamples, concluding that this notion of natural kind is not in tune with scientific classification and ought to be rejected in favor of an alternative. (shrink)

If the term "relativism" is understood as relativists take it, everyone is a relativist. If, on the other hand, one understands "relativism" as absolutists do, no one really could consistently be a relativist, despite what they might think. As I hope to show, however, much of this positioning of persons and philosophies is foolish. It misses much that is important in philosophical discussion and focuses attention in directions that lead to dead ends.

According to the received translational interpretation of incommensurability, incommensurability is viewed as untranslatability due to radical variance of meaning or reference of the terms in two competing scientific languages. The author argues that the translational approach to incommensurability does not effectively clarify the concept of incommensurability. Since it cannot provide us with tenable, integrated concept of incommensurability, it should be rejected.

According to the accepted translation-failure interpretation, the problem of incommensurability involves the nature of the meaning-referential relation between scientific languages. The incommensurability thesis is that some competing scientific languages are mutually untranslatable due to the radical variance of meaning or/and reference of the terms they employ. I argue that this interpretation faces many difficulties and cannot give us a tenable, coherent, and integrated notion of incommensurability. It has to be rejected. ;On the basis of two case studies, I find that (...) the confrontations between many classical incommensurable languages are not confrontations between two untranslatable languages with different distribution of truth values, but rather the confrontations between incompatible fundamental presuppositions at the ontological level. We can always identify a truth-value gap between two incommensurable languages. Such a truth-value gap indicates a communication breakdown between the two language communities on the one hand, and is caused by the incompatible fundamental presuppositions underlying them on the other. ;I thereby identify the truth-value functional relationship between sentences, instead of the meaning-referential relationship between terms, as the dominant semantic relation between two incommensurable languages. According to my presuppositional interpretation of incommensurability, the real secret of incommensurability lies in the ontological setup of two competing presuppositional languages. When two presuppositional languages with incompatible factual commitments encounter with each other, the confrontation leads to a truth-value gap, and consequently a communication breakdown between them. Formally put, two scientific languages are incommensurable when core sentences of one language, which have truth values when considered within its own context, lack truth values when considered within the context of the other due to an ontological gap between them. ;The presuppositional interpretation makes many significant contributions to the discussion of the issue of incommensurability and the related metaphysical and epistemological issues: It confirms the existence of the phenomenon of incommensurability and makes it metaphysically and epistemologically significant. It establishes the tenability and integrity of the notion of incommensurability. It avoids many alleged unattractive epistemological and metaphysical consequences of the translation-failure interpretation. (shrink)

This is an Italian translation of a lecture on incommensurability given at the University of Genoa.

The incommensurability thesis is the thesis that the content of some alternative scientific theories is incomparable due to translation failure between the vocabulary the theories employ. This paper presents an overview of the main issues which have arisen in the debate about incommensurability. It also briefly outlines a response to the thesis based on a modified causal theory of reference which allows change of reference subsequent to initial baptism, as well as a role to description in the determination of reference. (...) On such a view. the content of theories may be compared on the basis of shared reference, despite failure of translation. Two recent developments involving the incomnensurability thesis are also examined: (i) the taxonomic version of the incomensurability thesis found in Kuhn’s later writings. (ii) Hoyningen-Huenc’s neo-Kantian interpretation of Kuhn’s metaphysics. (shrink)

The book is an “introductory” reconstruction of Davidson on interpretation —a claim to be taken with a grain of salt. Writing introductory books has become an idol of the tribe. This is a concise book and reflects much study. It has many virtues along with some flaws. Ramberg assembles themes and puzzles from Davidson into a more or less coherent viewpoint. A special virtue is the innovative treatment of incommensurability and of the relation of Davidson’s work to hermeneutic themes. The (...) weakness comes in a certain unevenness. While generally convincing and well written, the book has low points which may leave the reader confused or unconvinced. Davidson is the hero in this book, and our hero is sometimes over idealized. (shrink)

What factors are involved in the resolution of scientific disputes? What factors make the resolution of such disputes rational? The traditional view confers an important role on observation statements that are shared by proponents of competing theories. Rival theories make incompatible (sometimes contradictory) observational predictions about a particular situation, and the prediction made by one theory is borne out while the prediction made by the other is not. Paul Feyerabend, Thomas Kuhn, and Paul Churchland have called into question this account (...) of theory-resolution. According to these philosophers, substantially different and competing scientific theories are semantically incommensurable: those theories do not share a common observation language. Two charges have been leveled against the semantic incommensurability theories. The first is that it ignores that some semantic features of observational terms (e.g., their reference) can be expressed by proponents of competing theories. The second is that the semantic incommensurability thesis is self-defeating. In this paper I will argue that both of these charges are true but not for the reasons usually given. (shrink)

I confront Feyerabend's position and critical rationalism in order to have a foundation or starting point for my (historical) investigation. The main difference of his position towards falsificationism is the belief that different theories cannot be discussed rationally. Feyerabend is convinced that Galilei's observations with the telescope in the historical context of the Copernican revolution supports his criticism. In particular, he argues that the Copernican theory was supported by deficient hypotheses, and falsifications were disposed by ad hoc hypotheses and propaganda. (...) Furthermore, he claims that his philosophy of science reconstructs Galilei's defence of the Copernican theory. He introduces a central principle of his position (the principle of tenacity) in order to justify a research strategy of not eliminating falsified theories. He tries to show that the tenacious defence of a theory corresponds to Galilei's defence of the Copernican theory. Remarkably, Feyerabend's approach to explain the development of science earns an important support from his interpretation of Galilei's observations. On this basis I give a falsificationist interpretation of Galilei's observations with the telescope, and oppose this interpretation to Feyerabend's. From a falsificationist perspective, auxiliary hypotheses compete during the Copernican revolution which can (with some effort) be critically discussed. Then I analyse the historical case in order to test Feyerabend's interpretation of the Copernican revolution. Inter alias I investigate thoroughly whether Galilei, as Feyerabend claims, immunised falsifications of the Copernican theory by the introduction of ad hoc hypotheses. The investigation considers Galilei's explanation of Venus' phases, his establishment of the irradiation hypothesis, the explanation of the telescope's functionality, and the role of the reproducibility of the observations with the telescope. Finally I provide a rational reconstruction of Galilei's falsification of the Ptolemaic theory. The formalisation shows that Galilei was not a cautious critical rationalist, but a very confident scientist using the method of falsification. (shrink)