Past exam of the history of science supplementary subject of the University of Oxford / 2018 (A14138W1)

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Acceptance was conditional, selective and historically constructed. Christian university authorities could employ Aristotelian natural philosophy because it offered a powerful account of an intelligible natural order and a teachable framework for reasoning about it. They did not thereby endorse every conclusion of Aristotle. The distinction between adopting an intellectual framework and granting its author unlimited authority is essential across this long period.

The attraction was partly explanatory. Aristotle treated natural objects as things with characteristic capacities for change, rather than as arbitrary collections of appearances. His distinctions between matter and form, potentiality and actuality, and the four causes supplied a connected vocabulary for discussing living bodies, physical change and explanation. Final cause could make the regular organization of nature intelligible in terms of ends. Such an ordered world was compatible with a creator whose works could be investigated through reason. Compatibility did not require identifying Aristotle's own conception of divinity with Christian doctrine.^[ref]

There were also institutional advantages. A curriculum organized around authoritative texts provided a common sequence of study, established questions for commentary, and standards for evaluating an argument. Aristotelian logic was useful in theology and other learned disciplines as well as in natural philosophy. Training students to distinguish a valid inference from an unsupported assertion could serve religious education. The university did not have to choose between intellectual discipline and religious authority: authorities could present disciplined reasoning as part of the preparation required for higher study.

The Paris statutes of 1215 nevertheless provide a decisive counterexample to any claim of uninterrupted acceptance. They prescribed the teaching of Aristotle's logical works while prohibiting his books of natural philosophy and metaphysics. The same document therefore exhibits both appropriation and restriction. A ban on particular books at one institution is not evidence that every Christian institution rejected all reasoning associated with Aristotle; conversely, later prominence does not erase the earlier prohibition.^[ref]

Thomas Aquinas illustrates a different strategy from wholesale prohibition. An argument could be philosophically valuable while failing to establish a revealed article of faith. Discussing the world's beginning, he rejected a necessary eternal world but also denied that reason could demonstrate its temporal beginning. Creation's dependence on God and a demonstrable beginning in time were distinct claims. This allowed extensive use of philosophical reasoning without letting an allegedly Aristotelian demonstration override revelation. It was not a doctrine that two contradictory propositions become true in separate compartments: the point was to distinguish the powers and limits of different kinds of justification.^[ref]

The resulting scholastic natural philosophy was consequently an interpreted tradition. Commentators could alter an explanation, distinguish its senses or deny that a particular conclusion followed, while retaining the questions and much of the vocabulary. This made the tradition more adaptable than a picture of students merely repeating an ancient book suggests. It also made departures possible from within university learning rather than only from outside it.

Its persistence into the seventeenth century should not be mistaken for scientific immobility or universal agreement. Galileo Galilei's telescopic account of lunar irregularities challenged a familiar contrast between terrestrial change and perfect celestial bodies. Yet the very argument addressed inherited problems about the constitution of the heavens. New observations could undermine particular Aristotelian claims without instantly replacing every part of a university curriculum.^[ref] The best explanation of acceptance is therefore a combination of explanatory usefulness, institutional entrenchment and selective theological accommodation. None establishes that acceptance was complete throughout 1200–1650.

There were major transformations worth calling revolutionary, but not one event that created a single modern method everywhere at once. The term Scientific Revolution is useful if it identifies a connected set of changes in problems, instruments, explanations and intellectual authority. It becomes misleading when it substitutes a sudden victory of reason over an undifferentiated earlier ignorance for an explanation of those changes.

One substantial transformation concerned the relation between mathematics and physical explanation. Newton's laws of motion and Newton's law of universal gravitation connected terrestrial and celestial motion within the same quantitative framework. The importance of this achievement was not simply a more accurate table of planetary positions. Kepler's laws of planetary motion could become consequences of a dynamical account, while deviations from simple planetary paths became problems of interacting bodies. A theory could now generate further quantitative questions about the Moon, comets and the figure of the Earth. This was a change in what an adequate physical explanation might accomplish.^[ref]

A second transformation concerned evidence. In 1610 Galileo Galilei presented a telescope as a means of investigating objects that ordinary unaided observation could not resolve. The changing appearances of bodies near Jupiter supported the existence of satellites accompanying that planet; the disposition of light and shadow on the Moon supported an irregular surface. These observations challenged the claim that all celestial bodies displayed a uniquely perfect constitution. They also required arguments about the reliability of the instrument and the interpretation of what appeared through it.^[ref] They did not, by themselves, uniquely establish the Earth's motion: a system in which planets circled the Sun while the Sun circled the Earth could accommodate satellites of Jupiter. Distinguishing a result from the stronger worldview later associated with it prevents a misleading account of instant conversion.

Programmes for producing knowledge also changed. Francis Bacon criticized premature generalization and proposed organized movement between observations, experiments and increasingly general claims. His comparison of the ant, spider and bee rejected both the mere accumulation of facts and reasoning spun entirely from the mind. The ambition was a cooperative, productive investigation of nature, with procedures for correcting habitual intellectual mistakes.^[ref] This programme is evidence for a methodological reform movement, not proof that every successful seventeenth-century investigator followed one Baconian algorithm.

The discontinuities were nevertheless built from inherited resources. Aristotelian natural philosophy already asked about causes and systematic knowledge; astronomy had long depended on demanding mathematical and observational practices. Instrument making depended on craft skills. Galileo Galilei's discovery claims also depended on patronage: his dedication and naming of the newly observed bodies in Sidereus Nuncius by Galileo Galilei explicitly linked celestial investigation to the Medici court. A socially situated discovery need not be scientifically false, but its circulation cannot be explained solely by the logical content of a theory.^[ref]

Nor did change imply a uniform retreat of religion. The General Scholium by Isaac Newton coupled the rejection of Cartesian vortices with an argument about divine government. That addition first appeared in 1713, so it should not be silently placed in the 1687 first edition. Its combination of physical argument and theology nevertheless rules out a simple narrative in which successful mathematical physics necessarily became religiously indifferent.^[ref]

Steven Shapin's challenge to a single, self-evident Scientific Revolution is therefore a useful warning about the historian's category, rather than a reason to deny every substantial change.^[ref] The strongest qualified verdict is that a revolutionary reorganization occurred in several influential European traditions, especially mathematical natural philosophy and instrumental observation. Its chronology, geographical reach and relation to other disciplines must be demonstrated separately. The category explains something only when those differences remain visible.

The Newtonian achievement combined a dynamical framework, a universal gravitational interaction and a distinctive standard of physical explanation. It was problematic partly because its mathematical successes exceeded what it supplied as a physical mechanism. Calling it a system should not conceal the difference between Isaac Newton's own writings, their later development and simplified versions promoted by his followers.

The Philosophiae Naturalis Principia Mathematica by Isaac Newton began with definitions and the Newton's laws of motion. Inertia distinguished persistence in uniform rectilinear motion from changes requiring impressed force. Newton's second law related such changes to impressed force; Newton's third law required reciprocal interactions. The account also distinguished absolute and relative quantities, raising questions about the meaning of true motion. In modern notation, a central part of the programme is expressed byHere momentum, force, masses and separation have their modern notation, and $G$ is the gravitational constant; the display is not a quotation of Isaac Newton's symbols. Combining Newton's laws of motion with Newton's law of universal gravitation made it possible to explain a wide range of terrestrial and celestial phenomena together.^[ref]

The quantitative content matters. For an ideal circular orbit of a small body around a much larger mass $M$, centripetal acceleration gives, in modern notation,This restricted illustration recovers the period–radius relation in Kepler's third law. It is not a reconstruction of the full original proof for an elliptical orbit. More generally the same interaction could account for the Moon's departure from a straight path, the paths of comets and mutual perturbations. Universal attraction made celestial irregularities potential consequences of a common law rather than reasons to assign a separate nature to each class of object.

The associated Newtonian programme extended beyond gravity. In optics, experiments on refraction supported the heterogeneous composition of white light: a prism could separate constituents with different refrangibilities rather than manufacture colours from a previously homogeneous ray. This challenged accounts that treated colour primarily as a modification introduced by the medium. It belongs to the broader Newtonian programme, although the 1704 Opticks by Isaac Newton must not be conflated with the content or publication date of the 1687 Philosophiae Naturalis Principia Mathematica by Isaac Newton.^[ref]

The greatest conceptual difficulty concerned action at a distance. For a defender of a contact mechanism, the mutual attraction of bodies through empty space appeared to reintroduce an occult quality instead of explaining an interaction. Cartesian vortices offered at least a material picture of how bodies might be carried around, whereas an inverse-square force law did not specify what transmitted the influence. Isaac Newton could point to the difficulties of reconciling such vortices with planetary periods and the varied paths of comets, but defeating that particular mechanism did not itself furnish an alternative mechanical cause.^[ref]

It is particularly important that Isaac Newton did not simply identify unmediated attraction as an essential property of matter. In his letter to Richard Bentley of 25 February 1692/3, he rejected that attribution and left open whether the relevant agent was material or immaterial. In the General Scholium by Isaac Newton, he distinguished establishing how gravity acts from assigning a cause not warranted by the phenomena.^[ref][ref]

Other difficulties followed from the standard of demonstration itself. The demanding geometry made the work hard to master; approximations and mutual interactions meant that apparent agreement had to be earned through calculation, not assumed from a slogan about universal attraction. Absolute motion and divine government also raised philosophical questions that a successful orbital calculation could not settle. Initial resistance thus included reasonable disputes about mechanism, evidence and explanatory adequacy. The system's later authority came from its capacity to sustain successful investigation despite those unresolved foundations, not from having answered every foundational question at publication.

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.

Geological inquiry weakened the Bible's standing as a sufficient technical chronology of the Earth, while producing several different religious responses. The authority of a text to date rocks, its authority as a record of human events and its religious authority were distinguishable. Between 1780 and 1850 they did not necessarily rise or fall together, and Christian readers did not all defend the same interpretation.

The difficulty was not simply that someone proposed an exceptionally large number for the Earth's age. Stratigraphy could establish a succession of events for which a short, single catastrophic history was inadequate. At Jedburgh, James Hutton described steeply inclined older beds truncated beneath much more nearly horizontal younger deposits. Rounded fragments of the older material occurred in an intervening conglomerate. A natural reconstruction required deposition of the older beds, their consolidation and disturbance, exposure and removal of material, and later deposition. The fragments supplied evidence that the older material had already become rock before it was worn down and incorporated into the younger formation. The unconformity was therefore an argument about an ordered history, not merely an impressive landscape.^[ref]

Such sequences supported deep time without supplying a radiometric age. No radiometric dating was available in this period, and a modern numerical age of the Earth must not be put into these authors' mouths. The accumulation of many independently inferred episodes instead changed what counted as a plausible timescale. James Hutton's cycles of destruction and renewal also belonged to a vision of an inhabitable, ordered Earth. His opening appeal to wisdom and purpose shows why the investigation cannot simply be equated with an intention to abolish religious explanation.^[ref]

Fossils created a related difficulty. Comparisons of fossil and living animals supported extinction, and differing fossil assemblages could mark successive conditions. Georges Cuvier's reconstruction of lost animals thus made the geological past different from the present. Yet catastrophic change did not necessarily mean a recent creation of the whole Earth. In the 1827 English Essay on the Theory of the Earth by Georges Cuvier (1827), a recent major revolution was distinguished from earlier revolutions and earlier populations of animals. A chronology assigned to the latest event was not automatically the age of every underlying formation.^[ref]

This distinction also complicates a simple opposition between biblical catastrophism and irreligious uniformitarianism. Robert Jameson's additions to that English edition explicitly related geological revolutions to the Mosaic deluge. Those additions must be identified as editorial material rather than silently attributed to Georges Cuvier. The volume demonstrates an attempt to make geological evidence corroborate sacred history even while recognizing a more extended sequence of changes. Disagreement therefore concerned which event a biblical account described and how its historical testimony should be compared with physical evidence.^[ref]

Charles Lyell's Principles of Geology by Charles Lyell (1830) made explanation by causes now in operation a programme stated in its very title. This shifted authority toward comparison with observable processes rather than using a scriptural narrative as a ready-made geological mechanism. But uniformitarianism contains separable commitments: continuity of natural laws does not logically imply an unchanging rate for every process, and neither claim by itself determines the interpretation of a biblical text. Conversely, acceptance of major catastrophes does not logically require accepting a universal Noachian flood as the explanation of every deposit.^[ref]

Religious accommodation remained a live response. The title and purpose of William Buckland's 1836 Geology and Mineralogy Considered with Reference to Natural Theology by William Buckland are themselves evidence that a leading geological work could present the new knowledge as material for natural theology, rather than treat the subject as intrinsically hostile to religion.^[ref] What became harder to sustain was an interpretation that required all geological formations and their organic succession to fit one short chronology and one flood. The result by 1850 was a redistribution and contestation of interpretive authority, not the uniform disappearance of the Bible's cultural or religious authority.

Originality lay chiefly in an explanatory mechanism and a sustained evidential synthesis, rather than in the first suggestion that living forms might change. Charles Darwin combined existing problems and resources in a new way, while Alfred Russel Wallace's independent work prevents the mechanism of natural selection from being assigned to a wholly solitary origin.

Jean-Baptiste Lamarck had already offered a connected account of the transformation of living forms. His explanation gave substantial roles to changed circumstances, altered habits, use and disuse, and the transmission of acquired modifications. This was a serious attempt to explain organic change, not simply the absurd proposition that an animal obtains anything it wishes for. Nevertheless, a process that transforms individuals through altered activity differs from differential persistence and reproduction among variants. Recognizing that difference allows comparison without pretending that every earlier idea of evolution was already natural selection.^[ref]

Charles Darwin also drew on practices that were not inventions of an isolated theorist. Breeders' artificial selection demonstrated that cumulative choice among inherited differences could alter domestic forms. Thomas Robert Malthus's population argument made unrestricted multiplication and limited subsistence a problem requiring explanation. Geology, the fossil record and the geographical distribution of organisms supplied historical and spatial patterns that a theory of species had to address. None of these ingredients alone entailed Charles Darwin's conclusion. A population check might eliminate individuals without producing cumulative adaptive change; breeding involved a human chooser whose intentions could not simply be projected into nature.^[ref]

The distinctive inference joined inherited differences to unequal success in leaving descendants. If some variants leave more surviving offspring under particular conditions, and some relevant differences recur in their descendants, the composition of a population can change over successive generations. Natural selection consequently requires neither an organism's foresight nor a breeder intentionally specifying its destination. Competition also has a wider meaning than physical combat: it includes dependence on other organisms and on conditions necessary for reproduction. In this way an apparently purposive fit between organism and environment could be given a historical explanation.^[ref]

Charles Darwin's larger contribution was to make that process part of a theory of branching common descent. Divergence, extinction, the affinities used in classification, the distribution of organisms on islands and continents, and similarities of structure could be treated as connected consequences of a history of descent with modification. The argument accumulated partially independent kinds of evidence. It did not rest on displaying one adaptation and declaring that the rest of organic history must follow. It also openly discussed difficulties, including complex organs, hybridism and imperfections in the fossil record.^[ref]

The case of Alfred Russel Wallace is decisive for judging intellectual priority. In the Introduction to the 1859 On the Origin of Species by Charles Darwin, Charles Darwin explicitly acknowledged the arrival of Alfred Russel Wallace's memoir and the publication of their materials together. Alfred Russel Wallace's essay on varieties departing from the original type argued that struggle could favour particular variants and permit continuing divergence. Its later reprint identifies the 1858 publication and distinguishes that essay from subsequent additions to the collected volume.^[ref][ref] Independent convergence shows both that the mechanism was a real intellectual achievement and that the surrounding problems and observations were not private possessions.

Finally, the historical theory must be distinguished from later genetics. Charles Darwin did not possess a Mendelian explanation of heredity, and the 1859 book allowed roles for use and disuse and other causes of variation. It is therefore inaccurate to identify its entire content with a modern opposition between strictly genetic natural selection and a wholly separate Lamarckian alternative.^[ref] The qualified judgment is that Charles Darwin produced an unusually powerful synthesis and a major new causal argument, independently paralleled by Alfred Russel Wallace. Dependence on predecessors limits a claim of creation from nothing; it does not reduce the theory to the repetition of those predecessors.

Literal miniature-organism theories had lost their former standing, but the explanatory problem had been transformed rather than abolished. By 1900, arguments about inherited organization, cellular differentiation and the response of an embryo to intervention were central to embryology. These were recognizably related to the older contrast between preformationism and epigenesis, even though neither eighteenth-century label could be carried unchanged into the new work.

The basic distinction concerned how organization arose. In preformationism, development unfolded organization already present in the germ; an increase in visible size did not require the original construction of the organism's arrangement. Epigenesis treated organs and differentiated structures as arising progressively. These broad positions left many further questions open. A claim that new visible organs appeared did not itself explain the material conditions that generated them, while a claim about inherited organization did not necessarily require a fully formed microscopic adult. Failure to separate these levels makes an apparent victory over the crudest miniature-organism picture look like the solution of every developmental problem.

August Weismann's discussion supplies contemporary evidence that the old opposition remained analytically useful in altered form. In the 1889 Essays upon Heredity and Kindred Biological Problems by August Weismann, he distinguished older miniature-animal preformationism from more recent accounts involving organized hereditary material. He discussed Charles Darwin's pangenesis under the latter category. That classification is not a claim that Charles Darwin literally believed in a tiny complete adult: it identifies a theory in which material representatives of parts contribute to the germ. The same discussion contrasted this with an epigenetic process in which an initial material constitution generates successive developmental states.^[ref]

August Weismann's germ plasm also relocated the problem of continuity between generations. A continuity of hereditary material could distinguish reproduction of the lineage from changes acquired by the body. But identifying continuity did not by itself establish how different parts of an embryo received different developmental capacities. A hypothesized partition of hereditary determinants during successive divisions offered one possible explanation. That possibility could be investigated by intervening on an embryo, rather than only inspecting it with an optical microscope.

The contrast between Wilhelm Roux and Hans Driesch makes the continuing issue concrete. In the frog experiment published in 1888, Wilhelm Roux killed one of the first two blastomeres with a heated needle and observed development of a partial embryo from the survivor. The result suggested mosaic development: an early part might possess a restricted developmental contribution. It did not, without further assumptions, identify a particular material in the nucleus as the cause. Nor was killing a cell and leaving it in place equivalent to cleanly separating the two living cells.

In trials begun in 1891, Hans Driesch separated or isolated early sea-urchin blastomeres; some developed into smaller but whole larvae. This supported regulative development and contradicted the claim that the first division universally and irreversibly partitioned the capacities required for different halves of the animal. The different animal, manipulation and surviving material mattered. One could not infer from the contrasting outcomes alone that one investigator had simply observed correctly and the other incorrectly.^[ref]

These experiments did not prove an absence of structure in the egg, and they did not establish that every embryonic cell retained every developmental possibility at every stage. Regulative development can depend on existing organization and interactions. Equally, Hans Driesch's eventual advocacy of vitalism was an interpretation of the findings, not an observation directly forced by a whole larva. The source cited here is his 1908 retrospective of pre-1900 work; its later philosophical formulation must not be silently treated as the precise position held at the original trials.

The debate had therefore become irrelevant only in a narrow sense: the old binary, if taken to mean a tiny complete organism versus the production of organization from wholly unstructured matter, no longer adequately described the best questions. In a broader sense it remained active as a dispute over what was inherited, what became progressively determined and how parts depended on the whole. The emergence of experimental embryology changed the evidence by which those claims could be tested. It did not make the relation between heredity and biological development disappear, and it should not be redescribed using modern epigenetics as though that were simply a new name for historical epigenesis.

Selection is unavoidable in historical writing, but selecting only eventual winners corrupts the explanation of how scientific knowledge developed. A defensible account can judge a theory false while still asking why capable investigators accepted it, what it enabled them to do and how its rejection became justified. Historical explanation and endorsement are different activities.

The first problem is circularity. If significance means contribution to what is now accepted, the account first chooses its endpoint and then discovers a past that appears to have been moving toward it. Historical presentism substitutes later categories and standards for the questions available to the participants. Whig history of science then turns the selected sequence into a story of foreseen progress. The process looks inevitable because alternatives have been removed from the narrative, not because their historical impossibility has been demonstrated.

Phlogiston theory provides an instructive example. Rejecting it as an accurate modern account of combustion does not explain the experiments on different airs that were conducted within it. Joseph Priestley investigated a gas through its production, its effect on a flame and its respiratory properties. His description of dephlogisticated air records an important experimental achievement even though its theoretical name differs from the later account of oxygen. If his framework is omitted as merely foolish, the history loses both the investigator's reasons and part of the evidence on which the competing chemistry depended.^[ref]

The winner's side also resists tidy retrospective sorting. Antoine Lavoisier's Elements of Chemistry by Antoine Lavoisier integrated caloric theory and an erroneous universal acidifying role for oxygen with influential practices of material accounting and chemical nomenclature. Calling the entire package modern and therefore correct would be just as inaccurate as discarding all of Joseph Priestley's work. A historian needs to follow which practices, concepts and commitments were retained, modified or rejected, rather than assigning a single final truth value to a whole person.^[ref]

The second problem is causal omission. Published theories depended on instrument makers, assistants, collectors, translators, teachers and readers able to repeat or adapt operations. Restricting attention to celebrated authors treats these conditions as if they supplied themselves. The dedication in Sidereus Nuncius by Galileo Galilei demonstrates that even a canonical discovery claim was situated in patronage and reputation. Examining that setting explains part of its form and audience; it need not imply that the satellites of Jupiter were merely a social invention.^[ref]

The third problem is that an unsuccessful explanation can generate a productive investigation. Wilhelm Roux's interpretation of an injured frog embryo helped make controlled intervention central to embryology. Hans Driesch disagreed with important conclusions while explicitly crediting the experimental programme. A history that retained only the eventual lesson of regulative development would struggle to explain why the decisive manipulation was attempted, why its controls mattered or why the result was surprising.^[ref]

This is not an argument that all theories are equally good, or that a historian must reconstruct every discarded speculation in equal detail. Selection should be justified by the explanatory problem. An account of a particular measurement may concentrate on calibration and instruments; an account of a theory's acceptance may require rivals, teaching practices and institutional settings. Scientific evaluation can ask how well competing theories answered the evidence then available and how later tests altered the balance. Historical judgment can also identify unjustified claims. What it cannot do is use later success as a substitute for evidence about the earlier process.

The same caution applies to very large labels. Steven Shapin's discussion of the Scientific Revolution makes the category itself an object of investigation rather than an unquestioned starting point.^[ref] A good history can explain genuine advances and unequal achievements while keeping lost alternatives visible. Its aim is neither a procession of heroes nor a refusal to distinguish better from worse explanations, but an account of how particular judgments became possible and persuasive.