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Primary paper, PSA 1982, volume 2, pp. 669–688; the scanned publication carries 1983 copyright. The discussion distinguishes local translation difficulties from interpretation and learning a conceptual vocabulary. The chemical example connects phlogiston, element and principle.

The historical explanation that ordinary combustion and metallic calcination involve combination with oxygen, rather than release of phlogiston. It should not be extended into the false claim that every chemical acid contains oxygen.

The new chemistry prevailed because it coordinated experimental accounting, a persuasive interpretation of gases and a reproducible language of composition. Its success cannot be reduced to the isolated discovery of oxygen, to the first use of a balance, or to the claim that every part of Antoine Lavoisier's system was correct.

The crucial experimental change was to treat gases as material participants that must enter the account of a chemical reaction. In a simple version of phlogiston theory, a metal lost phlogiston when it became a calx. Yet the calx could weigh more than the original metal. This was a serious explanatory challenge, although it did not make every contemporary version of phlogiston theory logically identical or instantly untenable. The question was how to organize changes in solid material, gas volume and the properties of the surrounding air into one consistent account.

Antoine Lavoisier's sustained heating of mercury under a connected air reservoir provides a concrete example. Red calx formed while part of the confined air disappeared; the residual gas no longer supported ordinary combustion or respiration. Heating the red material more strongly released a gas that supported these processes exceptionally well, while restoring the metal. Recombining the released gas with the residual gas recovered the behaviour of ordinary air. The explanatory advantage was a connected cycle of transformations, rather than a single unexplained weighing. Importantly, his own narrative acknowledges combining results from repeated trials into its presentation: the textbook sequence should not be mistaken for one effortless, perfectly complete performance.^[ref]

The oxygen theory of combustion interpreted the increase in the mass of a calx as addition of a constituent of air. A closed material account could then relate consumed gas to the transformed solid. Conservation of mass served as a rule for experimental reasoning: one had to examine all the reactants and products, including otherwise easily missed gases. Antoine Lavoisier stated this accounting principle explicitly in his discussion of fermentation. It was not necessary to claim that he invented every earlier practice of weighing or all previous ideas about material conservation to recognize the power of making such accounting central to a system.^[ref]

The new account also supplied a language that trained its users to recognize composition. In the 1787 nomenclature collaboration, Louis-Bernard Guyton de Morveau, Claude Louis Berthollet, Antoine-François de Fourcroy and Antoine Lavoisier linked related names to related substances. The 1789 textbook organized a route from relatively simple substances to compounds and then to operations and apparatus. Thus chemical nomenclature was not merely a convenient set of labels attached after an experimental victory. It made the proposed system easier to learn, communicate and extend, while requiring a reader to adopt some of its theoretical distinctions.^[ref]

This was a collective and contested transition. Joseph Priestley and Carl Wilhelm Scheele had independently investigated the gas subsequently interpreted as oxygen. Joseph Priestley's description of unusually respirable air did not entail adopting the same explanation of it as Antoine Lavoisier. A shared experimental object could therefore support competing theoretical descriptions. The achievement was the construction and dissemination of a coherent explanatory package, not the possession of a gas inaccessible to every rival.^[ref][ref]

The limits of the victory are equally instructive. The caloric theory remained part of the system, and the table of simple substances was explicitly related to the available means of decomposition. Antoine Lavoisier's universal association of acidity with oxygen was false: hydrochloric acid, with formula $\mathrm{HCl}$, is a concrete oxygen-free counterexample. The permanence of the new chemical nomenclature did not require retaining all the assumptions embedded in its first construction.^[ref] The system triumphed through explanatory and practical advantages that survived correction. Neither its errors nor the rationality of some contemporary objections makes that achievement disappear.

Carl Wilhelm Scheele and Joseph Priestley independently prepared and investigated the gas now called oxygen; Antoine Lavoisier was central to interpreting it within a new account of combustion and chemical composition. Assigning a unique discoverer requires deciding whether discovery means first preparation, first public report, recognition of a distinct kind of gas, or a successful theoretical interpretation. The historical controversy is largely about why one of these achievements should be privileged over the others.

Carl Wilhelm Scheele's investigations, generally dated to the early 1770s, preceded publication of Chemical Treatise on Air and Fire by Carl Wilhelm Scheele in 1777. His work distinguished the component that sustained burning from the remainder of ordinary air. He obtained the active component through several chemical preparations, including heating suitable substances, and interpreted the results in terms of phlogiston. Delayed publication matters to public priority, but it does not show that the experimental work had not occurred. Equally, a publication date alone does not establish the precise date of every earlier trial.^[ref]

Joseph Priestley's 1775 account is unusually revealing because it records hesitation and revision. On 1 August 1774 he heated red mercury(II) oxide with a large burning lens and collected the released gas. A candle burned particularly strongly in it; later trials involving animals and comparison with nitric oxide helped him distinguish its properties from ordinary air. He initially lacked a settled understanding of what he had obtained. Calling the product dephlogisticated air eventually made it intelligible within his own framework: it had an unusually great capacity to accept the phlogiston supposedly released in burning and animal breathing.^[ref]

The modern chemical equation,is a useful reconstruction, but it must not be passed off as Joseph Priestley's own explanation. In modern terms, heating decomposes mercury(II) oxide into mercury and molecular oxygen. The eighteenth-century experimenter instead worked with such categories as calces and differently modified airs. The material operation can be recognized across the change in theory while the meaning of its product remains historically contested.

Antoine Lavoisier made a different contribution. His programme tracked what entered and left substances in calcination and combustion, placing gases within quantitative material balances. In the mercury experiment described in Elements of Chemistry by Antoine Lavoisier, a retort communicated with an enclosed supply of air over mercury. Prolonged heating formed a red calx and diminished the enclosed air. Stronger heating of the recovered calx released an especially combustion-supporting gas; adding it back to the residual air restored the properties of the original mixture. The persuasive feature was the linked decomposition and reconstruction, not just a single spectacular flame.^[ref]

That sequence supported the claim that air was a mixture and that calcination involved combining a metal with part of it. A metal could gain mass because material entered it from the air, without requiring an invisible substance to leave with anomalous properties. Conservation of mass made the weighing scale a constraint on the explanation. However, Antoine Lavoisier's entire system was not modern chemistry. He treated caloric as an explanatory principle and associated the newly named oxygen with the formation of all chemical acids. The latter universal claim is false: hydrochloric acid is an chemical acid whose solute, hydrogen chloride, contains hydrogen and chlorine but no oxygen. This concrete counterexample prevents us from defining discovery as possession of today's complete theory.^[ref]

There are consequently several legitimate allocations of credit. An investigator concerned with earliest preparation may emphasize Carl Wilhelm Scheele; one concerned with the well-documented 1774 experiment and its rapid communication may emphasize Joseph Priestley; one concerned with the explanatory reconstruction of combustion may emphasize Antoine Lavoisier. The last achievement depended on experimental results that the others had produced. Correct interpretation was neither a substitute for preparing the material nor an achievement wholly independent of communication between investigators.

Historians disagree because their accounts embody different pictures of scientific change. A simple accumulation story can make discovery look like identifying one additional item in a ready-made list of chemical elements. A conceptual-change story emphasizes that the list and its criteria were themselves changing: oxygen was not just another variety of modified air in the new chemistry. National priority narratives and the dramatic reputation of the Chemical Revolution can further encourage a single heroic winner. Yet replacing that winner with a collective label is insufficient unless the different experimental and theoretical contributions are explained.

The most defensible answer distributes credit while specifying the achievement. Carl Wilhelm Scheele and Joseph Priestley deserve independent experimental discovery credit; Antoine Lavoisier deserves central credit for the chemical interpretation and reorganization that gave oxygen its place in a new system. Discovery was a sequence of preparation, discrimination, communication and reinterpretation, rather than one instantaneous encounter with a theory-free fact.

Scientific knowledge is deeply shaped by historical context in the questions asked, evidence available and standards of credibility, but context does not make results arbitrary or determine their truth by itself. The strongest argument identifies mechanisms through which context enters inquiry and then examines what experimental or mathematical constraints can resist it. This avoids both the claim that facts emerge untouched by human activity and the opposite claim that a social explanation is a substitute for testing them.

First, inherited conceptual resources determine what an investigator initially thinks an observation might be. Joseph Priestley's experiments on oxygen illustrate this directly. Heating mercury(II) oxide produced an unusually combustion-supporting gas, but the experiment did not arrive labelled with a modern chemical formula. Phlogiston supplied an available vocabulary: the gas could be interpreted as exceptionally dephlogisticated air rather than a newly isolated chemical element. His own account acknowledges the difficulty of revising expectations even when striking observations appeared. This is specific evidence that interpretation has a history, rather than a general accusation that past investigators were irrational.^[ref]

Antoine Lavoisier's material balances reorganized the same field by treating the air consumed during calcination as a constituent incorporated into the product. The retort, enclosed air supply and quantitative examination of products made some interpretations more difficult to maintain. Yet his identification of oxygen as the universal acidifying principle was itself wrong: hydrogen chloride gives an chemical acid without containing oxygen. The example establishes two distinct conclusions. An interpretive framework helps make observations intelligible; further observations and successful alternative explanations can expose its limits. Historical situatedness is compatible with correction.^[ref]

Second, instruments and techniques shape what can become an observable object. In nineteenth-century embryology, an optical microscope did not simply magnify a transparent miniature adult. Investigators needed suitable organisms, controlled access to eggs and sperm, ways of preparing thin or fixed material, and conventions for ordering developmental stages. Transparent sea-urchin eggs and external fertilization made processes accessible that were much harder to observe in opaque mammalian material. Such a choice was productive but selective: knowledge gained from one organism needed further work before it could be generalized to others.^[ref]

The Wilhelm Roux–Hans Driesch comparison shows why the details of an intervention matter. Killing an attached frog blastomere and separating a living sea-urchin blastomere differ both in material and operation. Partial development in one setting and a complete small larva in another cannot honestly be flattened into an experiment with one obvious answer. Nevertheless, the second outcome constrains the universality of an exclusively fixed mosaic theory of development. A capacity for regulation is empirically established in the tested conditions even if disagreement remains about its explanation. Technical and theoretical contexts shape the result's significance without allowing the observer simply to choose its outcome.^[ref]

Third, social interests can supply a problem or analogy without fully fixing the resulting theory. Charles Darwin's adaptation of Thomas Robert Malthus's population argument is a clear case. A discussion of human subsistence helped him formulate a mechanism for changes among organisms. However, his broad struggle for existence includes dependence and physical conditions, not only direct competition. The resulting natural selection explanation must be evaluated through genetic variation, heredity and differential reproduction, not accepted or rejected merely because a stimulus came from political economy. The route by which a hypothesis is formed is a historical question; the evidence sustaining its application is a connected but distinct question.^[ref][ref]

Fourth, conventions of demonstration affect what a community can reliably criticize. Galileo Galilei's definitions of accelerated motion let readers derive a squared time relation and compare it with repeated descents on an inclined plane. A reader can dispute whether the apparatus sufficiently approximates the model, distinguish a rolling ball from a freely falling body, or check whether the mathematical conclusion follows. The idealization is historically chosen, but its consequences are not whatever the author wishes. For a constant acceleration from rest, the distance ratio for elapsed times in the ratio $1:2$ must be $1:4$; changing that conclusion requires changing the assumptions or the mathematics.^[ref]

These cases support degrees rather than a single all-purpose answer. Historical context strongly affects research priorities, available specimens, instruments, vocabularies and access to credibility. It also affects which uncertainties become urgent and which applications receive resources. Its influence on a particular measured relation or mathematical entailment must be demonstrated rather than presumed. The same social setting can sustain competing interpretations, and a mathematical framework can travel beyond the setting in which it was first developed. Conversely, the ability to reproduce a result elsewhere does not erase the historical work needed to make that reproduction possible.

Scientific knowledge is historically produced and materially constrained. Context helps explain why a claim was thinkable, testable and persuasive at a particular time; it does not alone tell us whether the claim survives comparison, intervention and criticism. A convincing history therefore traces both the circumstances that make knowledge possible and the resistant evidence through which those circumstances can themselves be challenged.

The transition from phlogiston theory to an oxygen theory of combustion, and the transition from Newtonian mechanics to special relativity, support a restricted account of incommensurability. They show changes in conceptual organization and standards of explanation. They do not establish that rival scientists cannot communicate, compare results or give reasons for preferring a new account.

In the chemical case, a common phlogistic treatment makes a metal a calx combined with phlogiston, so calcination removes the principle responsible for its metallic character. Antoine Lavoisier's treatment reverses the decomposition: a metal combines with part of the air to form the calx. In a closed vessel, the calx's gain in mass must be understood together with what happens to the remaining gas. The mercury-and-air investigation and the recovery of the gas from the calx organize these operations into a different account of composition. This is a change in the relations between elements, compounds and chemical processes, not merely a new name for an unchanged substance.^[ref]

For Thomas Kuhn, a translation which replaces every occurrence of phlogiston with one modern substance fails to preserve those interconnected roles. Yet historians can learn the earlier vocabulary and reconstruct the relevant experiments. His later account explicitly distinguishes interpretation and language-learning from a word-for-word translation into a fixed successor vocabulary. Local untranslatability does not imply that every term or observation is inaccessible to the other community.^[ref]

The mechanical example concerns the reorganization of space, time and motion. In special relativity, distant simultaneity depends on an inertial frame and a specified clock-synchronization procedure. Newtonian mechanics instead uses a common time independent of inertial motion. This affects more than numerical corrections to one law: it changes which events are simultaneous and how velocity and momentum are related.^[ref]

Nevertheless, quantitative comparison is possible. For an invariant rest mass $m$,Here $c$ is the speed of light and $\gamma$ the Lorentz factor. At $v=0.6c$, the respective momenta are $0.75mc$ and $0.6mc$, a directly comparable difference. For $v/c\ll 1$, the leading agreement explains an important domain of earlier success. It would be inaccurate to claim that modern special relativity invariably makes mass velocity-dependent: invariant rest mass remains invariant in this convention.

These examples therefore support conceptual discontinuity without total evidential isolation. Some explanatory aims and classifications change; many preparations, measurements and quantitative relations remain comparable. No unique algorithm follows from shared values such as accuracy and scope, but the absence of such an algorithm is weaker than the absence of rational assessment. The most defensible Kuhnian conclusion is local and historical: comparison can require learning a conceptual system, while still permitting criticism of both systems and empirically warranted preference between them.

The no-miracles argument, in its familiar form, principally supports claims about the truth or approximate truth of successful theories. It is not naturally an argument for the bare existence of theoretical entities independently of the correctness of what is said about them. Entity realism can share its interest in scientific success while relying on a different and more local evidential argument.

Hilary Putnam's formulation treats the success of mature science as something requiring explanation. If theories describe relevant features of the world approximately correctly, their predictive and practical achievements become intelligible. If their central claims are far removed from reality, the same success appears surprising. The proposed inference uses abductive reasoning: accept the explanatory account which best makes sense of the achievements. It is not a valid deduction from successful prediction to truth, since a false theory can yield true consequences.^[ref]

The content of the explanandum matters. If the achievement is a quantitatively accurate prediction from equations about charges, fields and interactions, saying merely that electrons exist leaves most of that accuracy unexplained. Their existence is compatible with innumerable false accounts of their behaviour. A realist explanation of this success must therefore retain some trustworthy description of relevant properties or structure, not only an inventory of entities. This need not mean accepting every idealization or every speculative extension of the full theory.

Ian Hacking's intervention-based case for entity realism shifts the emphasis. Once investigators reliably use electrons to produce or investigate other phenomena, the entities are functioning as experimental tools rather than merely appearing in an explanatory story. Their causal powers can be supported across different apparatuses and theoretical descriptions. This provides a way of committing to particular entities while remaining selective about high-level theory. The argument rests on how the entities are manipulated, not simply on the statement that an encompassing theory has been successful.^[ref]

That position has limits too. Identifying the instrument, controlling its effects and distinguishing those effects from alternatives require some theoretical assumptions. Entity realism cannot plausibly mean that an investigator believes literally nothing about the properties or causal roles of an entity. Its more defensible form distinguishes localized, repeatedly usable knowledge from commitment to a complete theoretical picture. One can accept robust causal regularities about an electron source without treating every claim of a fundamental theory as equally established.

The principal challenge to the general no-miracles argument is that history contains successful theories with rejected central posits. The pessimistic induction presses the example of theories of light which retained a mechanical luminiferous aether, or accounts of combustion which included phlogiston. Such cases defeat an unrestricted inference from some success to the truth of every central assertion. A selective realist may ask which parts produced the successful predictions and which relations survived change. That reply must identify those parts with evidence; labelling an entire abandoned theory approximately true without explaining the retained content would merely rename the problem.^[ref][ref]

A constructive empiricist can also agree that theories are successful while treating empirical adequacy, rather than full truth about unobservables, as the appropriate aim of acceptance. The dispute then includes whether explanatory superiority licenses belief in the proposed unobservable account. Calling alternatives miraculous does not settle that epistemic issue by definition.^[ref]

The resulting judgment is selective. The original explanatory form reaches beyond entity existence toward a trustworthy representation of how nature works. It can support entity commitments as part of that representation, but cannot by itself isolate entity realism from all theory realism. Conversely, experimental manipulation can provide particular reasons for entity belief without establishing the whole no-miracles inference. Both arguments are strongest when they specify the achievement, the alternatives and the exact realist commitment being defended.

There are good examples of incommensurability when the claim is that some scientific terms and standards cannot be carried unchanged from one framework into another. They do not establish that rival theories cannot be understood, compared or rationally assessed. The strongest cases concern local interrelations among concepts, rather than a total absence of common experience or language.

The chemical transition associated with phlogiston provides one example. In a phlogistic account, a metal could be treated as a calx combined with phlogiston, with calcination involving the removal of that principle. In an oxygen theory of combustion, the relation is reorganized: the metal combines with oxygen to form the calx. Replacing one word with another while leaving every explanatory relation fixed does not translate the earlier system into the later one. The classifications of elements, compounds and principles are implicated together.^[ref]

This illustrates semantic dependence within a conceptual network. It does not entail that historians cannot reconstruct earlier claims. They can learn how the older vocabulary was used, describe the associated operations and compare its expectations with experimental records. Thomas Kuhn's later treatment distinguishes such interpretation and language-learning from supplying a sentence-by-sentence translation into an unchanged later vocabulary. Explaining the earlier practice need not produce a modern expression which preserves every inferential role of each old term. The fact that the example can be discussed is therefore not, on its own, a refutation of this more restricted thesis.^[ref]

A second example is the changing classification of planets. An Earth-centred arrangement can classify the Sun and Moon with the wandering celestial bodies while excluding the Earth. A heliocentric model reorganizes those relationships: the Earth is a planet and the Moon orbits it. A word-by-word substitution loses a change in the categories and relations used to frame the problem. Yet the investigators can still share observations of apparent positions and disagree about how to explain them. A change in classification is not proof that they inhabit incomparable worlds.

The comparison of Newtonian and relativistic momentum is particularly useful for limiting the claim. With invariant rest mass $m_0$, modern special relativity gives $p=\gamma m_{0}v$, whereas Newtonian mechanics uses $p=mv$. Here $c$ is the speed of light and $\gamma$ is the Lorentz factor. For $v/c\ll 1$ and matched rest-mass convention,This supplies a precise comparison of predictions within a domain. It does not derive all the older interpretation from the newer one with every concept unchanged. Conversely, it would be false to claim that relativity universally replaces invariant mass by a velocity-dependent quantity: invariant rest mass is a standard part of the relativistic account. The historical use of relativistic mass must be distinguished from this convention. For example, at $v=0.6c$, the invariant rest mass is still $m_0$ while $p=0.75m_{0}c$; defining relativistic mass as $p/v$ would give $1.25m_0$. These conventions must not be silently identified. A changed conceptual setting and a controlled mathematical relation between models can coexist.

Methodological differences supply another sense of incommensurability. Investigators may disagree about which problems are central, how much explanatory mechanism is required or how competing virtues should be weighted. Such disagreement can obstruct an algorithmic verdict without abolishing shared values such as accuracy or consistency. Shared criteria may themselves be applied differently. Neither fact demonstrates that no reasons can be offered across the disagreement.^[ref]

The conclusion is accordingly local and discriminating. Chemical kinds, astronomical categories and physical quantities can change their roles in ways not captured by a simple dictionary of synonyms. These examples challenge an account of progress as the addition of truths expressed in an eternally fixed vocabulary. They do not establish wholesale untranslatability, the impossibility of learning a rival framework, equal evidential merit or the irrationality of theory choice. To defend a stronger conclusion one would need to identify the precise comparison that fails and explain why available interpretation, common observations and domain-limited mathematical correspondences cannot repair it.

The replacement is philosophically significant because it challenges the inference from a theory's practical success to the existence of its proposed entities. Phlogiston theory interpreted ordinary combustion and metallic calcination as the loss of phlogiston; the oxygen theory of combustion instead treated these processes as combination with oxygen. This changes the account of what matter is doing, not merely the spelling of an agreed substance. Antoine Lavoisier's systematic treatment links the new chemistry with quantitative mass accounting and a revised chemical nomenclature.^[ref]

For scientific realism, the difficulty is that a once-useful theoretical term may fail to refer. If earlier success coexisted with a nonexistent unobservable entity, present success alone cannot guarantee that every central term of our theories refers either. This is the force of the pessimistic induction; it rebuts an unrestricted success-to-truth inference rather than deductively proving every present theory false.^[ref]

Several replies reduce, but do not erase, the problem. A scientific realist can distinguish successful empirical regularities from the particular mechanisms used to explain them, retaining only claims independently supported by varied experiments. Structural realism can emphasize preserved quantitative relations; it must identify the actual relations and their physical interpretation rather than declaring any recurring mathematics a vindication. A causal account of reference may preserve a term across some mistaken descriptions, but it cannot automatically identify phlogiston with oxygen: their proposed roles in the reaction differ.

A defensible conclusion is therefore selective and fallible scientific realism. The historical episode motivates stricter criteria for commitment, including independent manipulation, cross-checks and successful novel tests. It does not force the view that all theoretical entities are mere instruments. Conversely, calling the abandoned theory approximately true without specifying which claims survived simply restates the difficulty.

Instrumentalism treats theoretical descriptions primarily as tools for organizing and predicting observations rather than as a literally true inventory of unobservable entities. Its attraction is epistemic economy: where empirical success is all the evidence establishes, using a successful calculation need not commit us to every mechanism appearing in it. The abandonment of phlogiston illustrates why such caution can be reasonable.

However, distinguish three claims: we can use a theory without believing it; we ought to suspend belief about some of its entities; and those entities do not exist or theoretical sentences are not truth-apt. The first is commonplace and does not establish the last two. Constructive empiricism interprets theoretical claims literally while distinguishing acceptance for empirical adequacy from belief in the whole theory. It therefore offers restraint without treating all theoretical language as a disguised calculation recipe.^[ref]

A scientific realist can answer that independent experimental access, successful interventions and unexpectedly accurate new predictions support some entities more strongly than mere curve fitting. The no-miracles argument treats this convergence as something needing explanation. The reply is not conclusive: explanatory success need not guarantee truth, and selectively retained successful theories can make retrospective success look stronger than it was. Equally, historical failures do not show that every present theoretical commitment is equally fragile.

There is therefore a good argument for instrumental use and selective suspension of belief where evidence does not discriminate ontologies. There is a weaker argument for universal instrumentalism about every scientific entity. A defensible position should compare the actual evidence for particular commitments and explain why empirical adequacy is the right stopping point, rather than infer global agnosticism from the bare possibility of error.

A historical account in which burning and related processes involved the release or transfer of a supposed principle, phlogiston. Its interpretation of metallic calces differed from the later account of oxidation.