The deductive-nomological model (DN model), also known as Hempel's model or Hempel–Oppenheim model or Popper–Hempel model, is a formal view of scientifically answering questions asking, "Why...?". DN model poses scientific explanation as a deductive structure—that is, one where truth of its premises entails truth of its conclusion—hinged on accurate prediction or postdiction of the phenomenon to be explained.
Through problems concerning humans' ability to define, discover, and know causality, DN model's initial formulation omitted it, thought to be incidentally approximated by realistic selection of premises that derive the phenomenon of interest from observed, starting conditions plus general laws. Still, DN model formally permitted causally irrelevant factors. Also, derivability from observations and laws sometimes yielded absurd answers.
Upon logical empiricism's 1960s fall, DN model was concluded a flawed or greatly incomplete model of scientific explanation, but remained an idealized version, and rather accurate for modern physics. In the early 1980s, revision to DN model emphasized maximal specificity for relevance of the conditions and axioms stated. Together with Hempel's inductive-statistical model, DN model forms scientific explanation's covering law model, as also termed, from critical angle, subsumption theory.
- Form 1
- Roots 2
- Growth 3
- Decline 4
- Strengths 5
- Weaknesses 6
- Covering action 7
- See also 8
- Notes 9
- Sources 10
- Further reading 11
The term deductive distinguishes DN model's intended determinism from the probabilism of inductive inferences. The term nomological follows the Greek word νόμος or nomos, meaning "law". DN model holds to a view of scientific explanation whose conditions of adequacy (CA), semiformal but stated classically, are derivability (CA1), lawlikeness (CA2), empirical content (CA3), and truth (CA4).
In DN model, a law counterfactual claims and thus suggesting what must be true, while following from a scientific theory's axiomatic structure.
The phenomenon to be explained is the explanandum—an event, law, or theory—whereas the premises to explain it are explanans, true or highly confirmed, containing at least one universal law, and entailing the explanandum. Thus, given the explanans as initial, specific conditions C1, C2 . . . Cn plus general laws L1, L2 . . . Ln, the phenomenon E as explanandum is a deductive consequence, thereby scientifically explained.
Aristotle's scientific explanation in Physics resembles DN model, an idealized form of scientific explanation. Aristotelian physics' framework—Aristotelian metaphysics—reflected the perspective of this principally biologist, who, amid living entities' undeniable purposiveness, formalized vitalism and teleology, an intrinsic morality in nature. With emergence of Copernicanism, however, Descartes introduced mechanical philosophy, then Newton rigorously posed lawlike explanation, both Descartes and especially Newton shunning teleology within natural philosophy. At 1740, David Hume staked Hume's fork, highlighted the problem of induction, and found humans ignorant of either necessary or sufficient causality. Hume also highlighted the fact/value gap, as what is does not itself reveal what ought.
Near 1780, countering Hume's ostensibly radical empiricism, Immanuel Kant highlighted extreme rationalism—as by Descartes or Spinoza—and sought middle ground. Inferring the mind to arrange experience of the world into substance, space, and time, Kant placed the mind as part of the causal constellation of experience and thereby found Newton's theory of motion universally true, yet knowledge of things in themselves impossible. Safeguarding science, then, Kant paradoxically stripped it of scientific realism. Aborting Francis Bacon's inductivist mission to dissolve the veil of appearance to uncover the noumena—metaphysical view of nature's ultimate truths—Kant's transcendental idealism tasked science with simply modeling patterns of phenomena. Safeguarding metaphysics, too, it found the mind's constants holding also universal moral truths, and launched German idealism, increasingly speculative.
Auguste Comte found the problem of induction rather irrelevant since enumerative induction is grounded on the empiricism available, while science's point is not metaphysical truth. Comte found human knowledge had evolved from theological to metaphysical to scientific—the ultimate stage—rejecting both theology and metaphysics as asking questions unanswerable and posing answers unverifiable. Comte in the 1830s expounded positivism—the first modern philosophy of science and simultaneously a political philosophy—rejecting conjectures about unobservables, thus rejecting search for causes. Positivism predicts observations, confirms the predictions, and states a law, thereupon applied to benefit human society. From late 19th century into the early 20th century, the influence of positivism spanned the globe. Meanwhile, evolutionary theory's natural selection brought the Copernican Revolution into biology and eventuated in the first conceptual alternative to vitalism and teleology.
Whereas Comtean positivism posed science as description, logical positivism emerged in the late 1920s and posed science as explanation, perhaps to better unify empirical sciences by covering not only fundamental science—that is, fundamental physics—but special sciences, too, such as biology, psychology, economics, and anthropology. After defeat of National Socialism with World War II's close in 1945, logical positivism shifted to a milder variant, logical empiricism. All variants of the movement, which lasted until 1965, are neopositivism, sharing the quest of verificationism.
Neopositivists led emergence of the philosophy subdiscipline philosophy of science, researching such questions and aspects of scientific theory and knowledge. Scientific realism takes scientific theory's statements at face value, thus accorded either falsity or truth—probable or approximate or actual. Neopositivists held scientific antirealism as instrumentalism, holding scientific theory as simply a device to predict observations and their course, while statements on nature's unobservable aspects are elliptical at or metaphorical of its observable aspects, rather.
DN model received its most detailed, influential statement by Carl G Hempel, first in his 1942 article "The function of general laws in history", and more explicitly with Paul Oppenheim in their 1948 article "Studies in the logic of explanation". Leading logical empiricist, Hempel embraced the Humean empiricist view that humans observe sequence of sensory events, not cause and effect, as causal relations and casual mechanisms are unobservables. DN model bypasses causality beyond mere constant conjunction: first an event like A, then always an event like B.
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- In the 17th century, René Descartes as well as Isaac Newton firmly believed in God as nature's designer and thereby firmly believed in natural purposiveness, yet found teleology to be outside science's inquiry (Bolotin, Approach to Aristotle's Physics, pp 31–33). By 1650, formalizing heliocentrism and launching mechanical philosophy, Cartesian physics overthrew geocentrism as well as Aristotelian physics. In the 1660s, Robert Boyle sought to lift chemistry as a new discipline from alchemy. Newton more especially sought the laws of nature—simply the regularities of phenomena—whereby Newtonian physics, reducing celestial science to terrestrial science, ejected from physics the vestige of Aristotelian metaphysics, thus disconnecting physics and alchemy/chemistry, which then followed its own course, yielding chemistry around 1800.
- Nicknames for principles attributed to Hume—Hume's fork, problem of induction, Hume's law—were not created by Hume but by later philosophers labeling them for ease of reference.
- By Hume's fork, the truths of mathematics and logic as formal sciences are universal through "relations of ideas"—simply abstract truths—thus knowable without experience. On the other hand, the claimed truths of empirical sciences are contingent on "fact and real existence", knowable only upon experience. By Hume's fork, the two categories never cross. Any treatises containing neither can contain only "sophistry and illusion". (Flew, Dictionary, "Hume's fork", p 156).
- Not privy to the world's either necessities or impossibilities, but by force of habit or mental nature, humans experience sequence of sensory events, find seeming constant conjunction, make the unrestricted generalization of an enumerative induction, and justify it by presuming uniformity of nature. Humans thus attempt to justify a minor induction by adding a major induction, both logically invalid and unverified by experience—the problem of induction—how humans irrationally presume discovery of causality. (Chakraborti, Logic, p 381; Flew, Dictionary, "Hume", p 156.
For more discursive discussions of types of causality—necessary, sufficient, necessary and sufficient, component, sufficient component, counterfactual—see Rothman & Greenland, Parascandola & Weed, as well as Kundi. Following is more direct elucidation:
A necessary cause is a causal condition required for an event to occur. A sufficient cause is a causal condition complete to produce an event. Necessary is not always sufficient, however, since other casual factors—that is, other component causes—might be required to produce the event. Conversely, a sufficient cause is not always a necessary cause, since differing sufficient causes might likewise produce the event. Strictly speaking, a sufficient cause cannot be a single factor, as any causal factor must act casually through many other factors. And although a necessary cause might exist, humans cannot verify one, since humans cannot check every possible state of affairs. (Language can state necessary causality as a tautology—a statement whose terms' arrangement and meanings render it is logically true by mere definition—which, as an analytic statement, is uninformative about the actual world. A statement referring to and contingent on the world's actualities is a synthetic statement, rather.)
Sufficient causality is more actually sufficient component causality—a complete set of component causes interacting within a causal constellation—which, however, is beyond humans' capacity to fully discover. Yet humans tend intuitively to conceive of causality as necessary and sufficient—a single factor both required and complete—the one and only cause, the cause. One may so view flipping a light switch. The switch's flip was not sufficient cause, however, but contingent on countless factors—intact bulb, intact wiring, circuit box, bill payment, utility company, neighborhood infrastructure, engineering of technology by Thomas Edison and Nikola Tesla, explanation of electricity by James Clerk Maxwell, harnessing of electricity by Benjamin Franklin, metal refining, metal mining, and on and on—while, whatever the tally of events, nature's causal mechanical structure remains a mystery.
From a Humean perspective, the light's putative inability to come on without the switch's flip is neither a logical necessity nor an empirical finding, since no experience ever reveals that the world either is or will remain universally uniform as to the aspects appearing to bind the switch's flip as the necessary event for the light's coming on. If the light comes on without switch flip, surprise will affect one's mind, but one's mind cannot know that the event violated nature. As just a mundane possibility, an activity within the wall could have connected the wires and completed the circuit without the switch's flip.
Though apparently enjoying the scandals that trailed his own explanations, Hume was very practical and his skepticism was quite uneven (Flew p 156). Although Hume rejected orthodox theism and sought to reject metaphysics, Hume supposedly extended Newtonian method to the human mind, which Hume, in a sort of antiCopernican move, placed as the pivot of human knowledge (Flew p 154). Hume thus placed his own theory of knowledge on par with Newton's theory of motion (Buckle pp 70–71, Redman pp 182–83, Schliesser § abstract). Hume found enumerative induction an unavoidable custom required for one to live (Gattei pp 28–29). Hume found constant conjunction to reveal a modest causality type: counterfactual causality. Silent as to causal role—whether necessity, sufficiency, component strength, or mechanism—counterfactual causality is simply that alteration of a factor prevents or produces the event of interest.
- Kundi M (2006). "Causality and the interpretation of epidemiologic evidence". Environmental Health Perspectives. 114 (7): 969–974.
- Hume noted that authors ubiquitously continue for some time stating facts and then suddenly switch to stating norms—supposedly what should be—with barely explanation. Yet such values, as in ethics or aesthetics or political philosophy, are not found true merely by stating facts: is does not itself reveal ought. Hume's law is the principle that the fact/value gap is unbridgeable—that no statements of facts can ever justify norms—although Hume himself did not state that. Rather, some later philosophers found Hume to merely stop short of stating it, but to have communicated it. Anyway, Hume found that humans acquired morality through experience by communal reinforcement. (Flew, Dictionary, "Hume's law", p 157 & "Naturalistic fallacy", pp 240–41; Wootton, Modern Political Thought, p 306.)
- Kant inferred that the mind's constants arrange space holding Euclidean geometry—like Newton's absolute space—while objects interact temporally as modeled in Newton's theory of motion, whose law of universal gravitation is a truth synthetic a priori, that is, contingent on experience, indeed, but known universally true without universal experience. Thus, the mind's innate constants cross the tongs of Hume's fork and lay Newton's universal gravitation as a priori truth.
- Chakravartty, "Scientific realism", §1.2 "The three dimensions of realist commitment", in SEP, 2013: "Semantically, realism is committed to a literal interpretation of scientific claims about the world. In common parlance, realists take theoretical statements at 'face value'. According to realism, claims about scientific entities, processes, properties, and relations, whether they be observable or unobservable, should be construed literally as having truth values, whether true or false. This semantic commitment contrasts primarily with those of so-called instrumentalist epistemologies of science, which interpret descriptions of unobservables simply as instruments for the prediction of observable phenomena, or for systematizing observation reports. Traditionally, instrumentalism holds that claims about unobservable things have no literal meaning at all (though the term is often used more liberally in connection with some antirealist positions today). Some antirealists contend that claims involving unobservables should not be interpreted literally, but as elliptical for corresponding claims about observables".
- Challenges to scientific realism are captured succinctly by Bolotin, Approach to Aristotle's Physics (SUNY P, 1998), pp 33–34, commenting about modern science, "But it has not succeeded, of course, in encompassing all phenomena, at least not yet. For it laws are mathematical idealizations, idealizations, moreover, with no immediate basis in experience and with no evident connection to the ultimate causes of the natural world. For instance, Newton's first law of motion (the law of inertia) requires us to imagine a body that is always at rest or else moving aimlessly in a straight line at a constant speed, even though we never see such a body, and even though according to his own theory of universal gravitation, it is impossible that there can be one. This fundamental law, then, which begins with a claim about what would happen in a situation that never exists, carries no conviction except insofar as it helps to predict observable events. Thus, despite the amazing success of Newton's laws in predicting the observed positions of the planets and other bodies, Einstein and Infeld are correct to say, in The Evolution of Physics, that 'we can well imagine another system, based on different assumptions, might work just as well'. Einstein and Infeld go on to assert that 'physical concepts are free creations of the human mind, and are not, however it may seem, uniquely determined by the external world'. To illustrate what they mean by this assertion, they compare the modern scientist to a man trying to understand the mechanism of a closed watch. If he is ingenious, they acknowledge, this man 'may form some picture of a mechanism which would be responsible for all the things he observes'. But they add that he 'may never quite be sure his picture is the only one which could explain his observations. He will never be able to compare his picture with the real mechanism and he cannot even imagine the possibility or the meaning of such a comparison'. In other words, modern science cannot claim, and it will never be able to claim, that is has the definite understanding of any natural phenomenon".
- Whereas a hypothetical imperative is practical, simply what one ought to do if one seeks a particular outcome, the categorical imperative is morally universal, what everyone always ought to do.
- Bourdeau, "Auguste Comte", §§ "Abstract" & "Introduction", in Zalta, ed, SEP, 2013.
- Comte, A General View of Positivism (Trübner, 1865), pp 49–50, including the following passage: "As long as men persist in attempting to answer the insoluble questions which occupied the attention of the childhood of our race, by far the more rational plan is to do as was done then, that is, simply to give free play to the imagination. These spontaneous beliefs have gradually fallen into disuse, not because they have been disproved, but because humankind has become more enlightened as to its wants and the scope of its powers, and has gradually given an entirely new direction to its speculative efforts".
- Flew, Dictionary (St Martin's, 1984), "Positivism", p 283.
- Woodward, "Scientific explanation", §1 "Background and introduction", in SEP, 2011.
- Friedman, Reconsidering Logical Positivism (Cambridge U P, 1999), p xii.
- Any positivism placed in the 20th century is generally neo, although there was Ernst Mach's positivism nearing 1900, and a general positivistic approach to science—traceable to the inductivist trend from Bacon at 1620, the Newtonian research program at 1687, and Comptean positivism at 1830—that continues in a vague but usually disavowed sense within popular culture and some sciences.
- Neopositivists are sometimes called "verificationists".
- Chakravartty, "Scientific realism", §4 "Antirealism: Foils for scientific realism", §4.1 "Empiricism", in SEP, 2013: "Traditionally, instrumentalists maintain that terms for unobservables, by themselves, have no meaning; construed literally, statements involving them are not even candidates for truth or falsity. The most influential advocates of instrumentalism were the logical empiricists (or logical positivists), including Carnap and Hempel, famously associated with the Vienna Circle group of philosophers and scientists as well as important contributors elsewhere. In order to rationalize the ubiquitous use of terms which might otherwise be taken to refer to unobservables in scientific discourse, they adopted a non-literal semantics according to which these terms acquire meaning by being associated with terms for observables (for example, 'electron' might mean 'white streak in a cloud chamber'), or with demonstrable laboratory procedures (a view called 'operationalism'). Insuperable difficulties with this semantics led ultimately (in large measure) to the demise of logical empiricism and the growth of realism. The contrast here is not merely in semantics and epistemology: a number of logical empiricists also held the neo-Kantian view that ontological questions 'external' to the frameworks for knowledge represented by theories are also meaningless (the choice of a framework is made solely on pragmatic grounds), thereby rejecting the metaphysical dimension of realism (as in Carnap 1950)".
- Okasha, Philosophy of Science (Oxford U P, 2002), p 62: "Strictly we should distinguish two sorts of anti-realism. According to the first sort, talk of unobservable entities is not to be understood literally at all. So when a scientist pus forward a theory about electrons, for example, we should not take him to be asserting the existence of entities called 'electrons'. Rather, his talk of electrons is metaphorical. This form of anti-realism was popular in the first half of the 20th century, but few people advocate it today. It was motivated largely by a doctrine in the philosophy of language, according to which it is not possible to make meaningful assertions about things that cannot in principle be observed, a doctrine that few contemporary philosophers accept. The second sort of anti-realism accepts that talk of unobservable entities should be taken at face value: if a theory says that electrons are negatively charged, it is true if electrons do exist and are negatively charged, but false otherwise. But we will never know which, says the anti-realist. So the correct attitude towards the claims that scientists make about unobservable reality is one of total agnosticism. They are either true or false, but we are incapable of finding out which. Most modern anti-realism is of this second sort".
- Woodward, "Scientific explanation", in Zalta, ed, SEP, 2011, abstract.
- Carl G Hempel & Paul Oppenheim, "Studies in the logic of explanation", Philosophy of Science, 1948 Apr;15(2):135–175.
- Bechtel, Discovering Cell Mechanisms (Cambridge U P, 2006), esp pp 24–25.
- Woodward, "Scientific explanation", §2 "The DN model", §2.3 "Inductive statistical explanation", in Zalta, ed, SEP, 2011.
- von Wright, Explanation and Understanding (Cornell U P, 1971), p 11.
- Stuart Glennan, "Explanation", § "Covering-law model of explanation", in Sarkar & Pfeifer, eds, Philosophy of Science (Routledge, 2006), p 276.
- Manfred Riedel, "Causal and historical explanation", in Manninen & Tuomela, eds, Essays on Explanation and Understanding (D Reidel, 1976), pp 3–4.
- Neopositivism's fundamental tenets were the verifiability criterion of cognitive meaningfulness, the analytic/synthetic gap, and the observation/theory gap. From 1950 to 1951, Carl Gustav Hempel renounced the verifiability criterion. In 1951 Willard Van Orman Quine attacked the analytic/synthetic gap. In 1958, Norwood Russell Hanson blurred the observational/theoretical gap. In 1959, Karl Raimund Popper attacked all of verificationism—he attacked, actually, any type of positivism—by asserting falsificationism. In 1962, Thomas Samuel Kuhn overthrew foundationalism, which was erroneously presumed to be a fundamental tenet of neopositivism.
- Fetzer, "Carl Hempel", §3 "Scientific reasoning", in SEP, 2013: "The need to dismantle the verifiability criterion of meaningfulness together with the demise of the observational/theoretical distinction meant that logical positivism no longer represented a rationally defensible position. At least two of its defining tenets had been shown to be without merit. Since most philosophers believed that Quine had shown the analytic/synthetic distinction was also untenable, moreover, many concluded that the enterprise had been a total failure. Among the important benefits of Hempel's critique, however, was the production of more general and flexible criteria of cognitive significance in Hempel (1965b), included in a famous collection of his studies, Aspects of Scientific Explanation (1965d). There he proposed that cognitive significance could not be adequately captured by means of principles of verification or falsification, whose defects were parallel, but instead required a far more subtle and nuanced approach. Hempel suggested multiple criteria for assessing the cognitive significance of different theoretical systems, where significance is not categorical but rather a matter of degree: 'Significant systems range from those whose entire extralogical vocabulary consists of observation terms, through theories whose formulation relies heavily on theoretical constructs, on to systems with hardly any bearing on potential empirical findings' (Hempel 1965b: 117). The criteria Hempel offered for evaluating the 'degrees of significance' of theoretical systems (as conjunctions of hypotheses, definitions, and auxiliary claims) were (a) the clarity and precision with which they are formulated, including explicit connections to observational language; (b) the systematic—explanatory and predictive—power of such a system, in relation to observable phenomena; (c) the formal simplicity of the systems with which a certain degree of systematic power is attained; and (d) the extent to which those systems have been confirmed by experimental evidence (Hempel 1965b). The elegance of Hempel's study laid to rest any lingering aspirations for simple criteria of 'cognitive significance' and signaled the demise of logical positivism as a philosophical movement".
- Popper, "Against big words", In Search of a Better World (Routledge, 1996), pp 89-90.
- Hacohen, Karl Popper: The Formative Years (Cambridge U P, 2000), pp 212–13.
- Logik der Forschung, published in Austria in 1934, was translated by Popper from German to English, The Logic of Scientific Discovery, and arrived in the Anglosphere in 1959.
- Reutlinger, Schurz & Hüttemann, "Ceteris paribus", § 1.1 "Systematic introduction", in Zalta, ed, SEP, 2011.
- As scientific study of cells, cytology emerged in the 19th century, yet its technology and methods were insufficient to clearly visualize and establish existence of any cell nucleus.
- The first famed biochemistry experiment was Edward Buchner's in 1897 (Morange, A History, p 11). The biochemistry discipline soon emerged, initially investigating colloids in biological systems, a "biocolloidology" (Morange p 12; Bechtel, Discovering, p 94). This yielded to macromolecular theory, the term macromolecule introduced by German chemist Hermann Staudinger in 1922 (Morange p 12).
- Cell biology emerged principally at Rockefeller Institute through new technology (electron microscope and ultracentrifuge) and new techniques (cell fractionation and advancements in staining and fixation).
- James Fetzer, ch 3 "The paradoxes of Hempelian explanation", in Fetzer J, ed, Science, Explanation, and Rationality (Oxford U P, 2000), pp 121–122.
- Fetzer, ch 3 in Fetzer, ed, Science, Explanation, and Rationality (Oxford U P, 2000), p 129.
- Bechtel, Philosophy of Science (Lawrence Erlbaum, 1988), ch 1, subch "Areas of philosophy that bear on philosophy of science", § "Metaphysics", pp 8–9, § "Epistemology", p 11.
- H Atmanspacher, R C Bishop & A Amann, "Extrinsic and intrinsic irreversibility in probabilistic dynamical laws", in Khrennikov, ed, Proceedings (World Scientific, 2001), pp 51–52.
- Fetzer, ch 3, in Fetzer, ed, Science, Explanation, and Rationality (Oxford U P, 2000), p 118, poses some possible ways that natural laws, so called, when epistemic can fail as ontic: "The underlying conception is that of bringing order to our knowledge of the universe. Yet there are at least three reasons why even complete knowledge of every empirical regularity that obtains during the world's history might not afford an adequate inferential foundation for discovery of the world's laws. First, some laws might remain uninstantiated and therefore not be displayed by any regularity. Second, some regularities may be accidental and therefore not display any law of nature. And, third, in the case of probabilistic laws, some frequencies might deviate from their generating nomic probabilities 'by chance' and therefore display natural laws in ways that are unrepresentative or biased".
- This theory reduction occurs if, and apparently only if, the Sun and one planet are modeled as a two-body system, excluding all other planets (Torretti, Philosophy of Physics, pp 60–62).
- Spohn, Laws of Belief (Oxford U P, 2012), p 305.
- Whereas fundamental physics has sought laws of universal regularity, special sciences normally include ceteris paribus laws, which are predictively accurate to high probability in "normal conditions" or with "all else equal", but have exceptions [Reutlinger et al § 1.1]. Chemistry's laws seem exceptionless in their domains, yet were in principle reduced to fundamental physics [Feynman p 5, Schwarz Fig 1, and so are special sciences.
- Bechtel, Philosophy of Science (Lawrence Erlbaum, 1988), ch 5, subch "Introduction: Relating disciplines by relating theories" pp 71–72.
- Bechtel, Philosophy of Science (Lawrence Erlbaum, 1988), ch 5, subch "Theory reduction model and the unity of science program" pp 72–76.
- Bem & de Jong, Theoretical Issues (Sage, 2006), pp 45–47.
- O'Shaughnessy, Explaining Buyer Behavior (Oxford U P, 1992), pp 17–19.
- Spohn, Laws of Belief (Oxford U P, 2012), p 306.
- Karhausen, L. R. (2000). "Causation: The elusive grail of epidemiology". Medicine, health care, and philosophy 3 (1): 59–67.
- Bechtel, Philosophy of Science (Lawrence Erlbaum, 1988), ch 3, subch "Repudiation of DN model of explanation", pp 38–39.
- Rothman, K. J.; Greenland, S. (2005). "Causation and Causal Inference in Epidemiology". American Journal of Public Health 95: S144–S150.
- Boffetta, "Causation in the presence of weak associations", Crit Rev Food Sci Nutr, 2010;50(S1):13–16.
- Making no commitment as to the particular causal role—such as necessity, or sufficiency, or component strength, or mechanism—counterfactual causality is simply that alteration of a factor from its factual state prevents or produces by any which way the event of interest.
- In epidemiology, the counterfactual causality is not deterministic, but probabilistic (Parascandola & Weed, "Causation in epidemiology", J Epidemiol Community Health, 2001;55:905–12) PubMed.
- Schwarz, "Recent developments in string theory", Proc Natl Acad Sci U S A, 1998;95:2750–7, esp Fig 1.
- Ben-Menahem, Conventionalism (Cambridge U P, 2006), p 71.
- Instances of falsity limited Boyle's law to special cases, thus ideal gas law.
- Newburgh et al, "Einstein, Perrin, and the reality of atoms", Am J Phys, 2006, p 478.
- For brief review of Boltmann's view, see ch 3 "Philipp Frank", § 1 "T S Kuhn's interview", in Blackmore et al, eds, Ernst Mach's Vienna 1895–1930 (Kluwer, 2001), p 63, as Frank was a student of Boltzmann soon after Mach's retirement. See "Notes", pp 79–80, #12 for views of Mach and of Ostwald, #13 for views of contemporary physicists generally, and #14 for views of Einstein. The more relevant here is #12: "Mach seems to have had several closely related opinions concerning atomism. First, he often thought the theory might be useful in physics as long as one did not believe in the reality of atoms. Second, he believed it was difficult to apply the atomic theory to both psychology and physics. Third, his own theory of elements is often called an 'atomistic theory' in psychology in contrast with both gestalt theory and a continuum theory of experience. Fourth, when critical of the reality of atoms, he normally meant the Greek sense of 'indivisible substance' and thought Boltzmann was being evasive by advocating divisible atoms or 'corpuscles' such as would become normal after J J Thomson and the distinction between electrons and nuclei. Fifth, he normally called physical atoms 'things of thought' and was very happy when Ostwald seemed to refute the reality of atoms in 1905. And sixth, after Ostwald returned to atomism in 1908, Mach continued to defend Ostwald's 'energeticist' alternative to atomism".
Physicists had explained the electromagnetic field's energy as mechanical energy, like an ocean wave's bodily impact, not water droplets individually showered (Grandy, Everyday Quantum Reality, pp 22–23). In the 1890s, the problem of blackbody radiation was paradoxical until Max Planck theorized quantum exhibiting Planck's constant—a minimum unit of energy. The quanta were mysterious, not viewed as particles, yet simply as units of energy. Another paradox, however, was the photoelectric effect.
As shorter wavelength yields more waves per unit distance, lower wavelength is higher wave frequency. Within the electromagnetic spectrum's visible portion, frequency sets the color. Light's intensity, however, is the wave's amplitude as the wave's height. In a strictly wave explanation, a greater intensity—higher wave amplitude—raises the mechanical energy delivered, namely, the wave's impact, and thereby yields greater physical effect. And yet in the photoelectric effect, only a certain color and beyond—a certain frequency and higher—was found to knock electrons off a metal surface. Below that frequency or color, raising the intensity of the light still knocked no electrons off.
Einstein modeled Planck's quanta as each a particle whose individual energy was Planck's constant multiplied by the light's wave's frequency: at only a certain frequency and beyond would each particle be energetic enough to eject an electron from its orbital. Although elevating the intensity of light would deliver more energy—more total particles—each individual particle would still lack sufficient energy to dislodge an electron. Einstein's model, far more intricate, used probability theory to explain rates of elections ejections as rates of collisions with electromagnetic particles. This revival of the particle hypothesis of light—generally attributed to Newton—was widely doubted. By 1920, however, the explanation helped solve problems in atomic theory, and thus quantum mechanics emerged. In 1926, Gilbert N Lewis termed the particles photons. QED models them as the electromagnetic field's messenger particles or force carriers, emitted and absorbed by electrons and by other particles undergoing transitions.
- Wolfson, Simply Einstein (W W Norton & Co, 2003), p 67.
- Newton's gravitational theory at 1687 had postulated absolute space and absolute time. To fit Young's transverse wave theory of light at 1804, space was theoretically filled with Fresnel's luminiferous aether at 1814. By Maxwell's electromagnetic field theory of 1865, light always holds a constant speed, which, however, must be relative to something, apparently to aether. Yet if light's speed is constant relative to aether, then a body's motion through aether would be relative to—thus vary in relation to—light's speed. Even Earth's vast speed, multiplied by experimental ingenuity with an interferometer by Michelson & Morley at 1887, revealed no apparent aether drift—light speed apparently constant, an absolute. Thus, both Newton's gravitational theory and Maxwell's electromagnetic theory each had its own relativity principle, yet the two were incompatible. For brief summary, see Wilczek, Lightness of Being (Basic Books, 2008), pp 78–80.
- Cordero, EPSA Philosophy of Science (Springer, 2012), pp 26–28.
- Hooper, Aether and Gravitation (Chapman & Hall, 1903), pp 122–23.
- Lodge, "The ether of space", Sci Am Suppl, 1909;67:202–03.
- Even Mach, who shunned all hypotheses beyond direct sensory experience, presumed an aether, required for motion to not violate mechanical philosophy's founding principle, No instant interaction at a distance (Einstein, "Ether", Sidelights (Methuen, 1922), pp 15–18).
- Rowlands, Oliver Lodge (Liverpool U P, 1990), pp 159–60: "Lodge's ether experiments have become part of the historical background leading up to the establishment of special relativity and their significance is usually seen in this context. Special relativity, it is stated, eliminated both the ether and the concept of absolute motion from physics. Two experiments were involved: that of Michelson and Morley, which showed that bodies do not move with respect to a stationary ether, and that of Lodge, which showed that moving bodies do not drag ether with them. With the emphasis on relativity, the Michelson–Morley experiment has come to be seen as the more significant of the two, and Lodge's experiment becomes something of a detail, a matter of eliminating the final, and less likely, possibility of a nonstationary, viscous, all-pervading medium. It could be argued that almost the exact opposite may have been the case. The Michelson–Morley experiment did not prove that there was no absolute motion, and it did not prove that there was no stationary ether. Its results—and the FitzGerald–Lorentz contraction—could have been predicted on Heaviside's, or even Maxwell's, theory, even if no experiment had ever taken place. The significance of the experiment, though considerable, is purely historical, and in no way factual. Lodge's experiment, on the other hand, showed that, if an ether existed, then its properties must be quite different from those imagined by mechanistic theorists. The ether which he always believed existed had to acquire entirely new properties as a result of this work".
- Mainly Hendrik Lorentz as well as Henri Poincaré modified electrodynamic theory and, more or less, developed special theory of relativity before Einstein did (Ohanian, Einstein's Mistakes, pp 281–85). Yet Einstein, free a thinker, took the next step and stated it, more elegantly, without aether (Torretti, Philosophy of Physics, p 180).
- Tavel, Contemporary Physics (Rutgers U P, 2001), pp , 66.
- Introduced soon after Einstein explained Brownian motion, special relativity holds only in cases of inertial motion, that is, unaccelerated motion. Inertia is the state of a body experiencing no acceleration, whether by change in speed—either quickening or slowing—or by change in direction, and thus exhibits constant velocity, which is speed plus direction.
- Cordero, EPSA Philosophy of Science (Springer, 2012), pp 29–30.
- To explain absolute light speed without aether, Einstein modeled that a body at motion in an electromagnetic field experiences length contraction and time dilation, which Lorentz and Poincaré had already modeled as Lorentz-FitzGerald contraction and Lorentz transformation but by hypothesizing dynamic states of the aether, whereas Einstein's special relativity was simply kinematic, that is, positing no causal mechanical explanation, simply describing positions, thus showing how to align measuring devices, namely, clocks and rods. (Ohanian, Einstein's Mistakes, pp 281–85).
- Ohanian, Einstein's Mistakes (W W Norton, 2008), pp 281–85.
- Newton's theory required absolute space and time.
Buchen, "May 29, 1919", Wired, 2009.
Moyer, "Revolution", in Studies in the Natural Sciences (Springer, 1979), p 55.
Melia, Black Hole (Princeton U P, 2003), pp 83–87.
- Crelinsten, Einstein's Jury (Princeton U P, 2006), p 28.
From 1925 to 1926, independently but nearly simultaneously, Werner Heisenberg as well as Erwin Schrödinger developed quantum mechanics (Zee in Feynman, QED, p xiv). Schrödinger introduced wave mechanics, whose wave function is discerned by a partial differential equation, now termed Schrödinger equation (p xiv). Heisenberg, who also stated the uncertainty principle, along with Max Born and Pascual Jordan introduced matrix mechanics, which rather confusingly talked of operators acting on quantum states (p xiv). If taken as causal mechanically explanatory, the two formalisms vividly disagree, and yet are indiscernible empirically, that is, when not used for interpretation, and taken as simply formalism (p xv).
In 1941, at a party in a tavern in Princeton, New Jersey, visiting physicist Herbert Jehle mentioned to Richard Feynman a different formalism suggested by Paul Dirac, who developed bra–ket notation, in 1932 (p xv). The next day, Feynman completed Dirac's suggested approach as sum over histories or sum over paths or path integrals (p xv). Feynman would joke that this approach—which sums all possible paths that a particle could take, as though the particle actually takes them all, canceling themselves out except for one pathway, the particle's most efficient—abolishes the uncertainty principle (p xvi). All empirically equivalent, Schrödinger's wave formalism, Heisenberg's matrix formalism, and Feynman's path integral formalism all incorporate the uncertain principle (p xvi).
There is no particular barrier to additional formalisms, which could be, simply have not been, developed and widely disseminated (p xvii). In a particular physical discipline, however, and on a particular problem, one of the three formalisms might be easier than others to operate (pp xvi–xvii). By the 1960s, path integral formalism virtually vanished from use, while matrix formalism was the "canonical" (p xvii). In the 1970s, path integral formalism made a "roaring comeback", became the predominant means to make predictions from QFT, and impelled Feynman to an aura of mystique (p xviii).
- Cushing, Quantum Mechanics (U Chicago P, 1994), pp 113–18.
- Schrödinger's wave mechanics posed an electron's charge smeared across space as a waveform, later reinterpreted as the electron manifesting across space probabilistically but nowhere definitely while eventually building up that deterministic waveform. Heisenberg's matrix mechanics confusingly talked of operators acting on quantum states. Richard Feynman introduced QM's path integral formalism—interpretable as a particle traveling all paths imaginable, canceling themselves, leaving just one, the most efficient—predictively identical with Heisenberg's matrix formalism and with Schrödinger's wave formalism.
- Torretti, Philosophy of Physics (Cambridge U P, 1999), pp 393–95.
- Torretti, Philosophy of Physics (Cambridge U P, 1999), p 394.
- Torretti, Philosophy of Physics (Cambridge U P, 1999), p 395.
- Recognition of strong force permitted Manhattan Project to engineer Little Boy and Fat Man, dropped on Japan, whereas effects of weak force were seen in its aftermath—radioactive fallout—of diverse health consequences.
- Wilczek, "The persistence of ether", Phys Today, 1999;52:11,13, p 13.
- The four, known fundamental interactions are gravitational, electromagnetic, weak nuclear, and strong nuclear.
- Grandy, Everyday Quantum Reality (Indiana U P, 2010), pp 24–25.
- Schweber, QED and the Men who Made it (Princeton U P, 1994).
- Feynman, QED (Princeton U P, 2006), p 5.
- Torretti, Philosophy of Physics, (Cambridge U P, 1999), pp 395–96.
- Cushing, Quantum Mechanics (U Chicago P, 1994), pp 158–59.
- Close, "Much ado about nothing", Nova, PBS/WGBH, 2012: "This new quantum mechanical view of nothing began to emerge in 1947, when 2, which implies that energy can congeal in material form, and you have a recipe for particles that bubble in and out of existence even in the void. This effect allowed Lamb to literally measure something from nothing".
- Vongehr "Higgs discovery rehabilitating despised Einstein Aether", Science 2.0, 2011.
- Vongehr, "Supporting abstract relational space-time as fundamental without doctrinism against emergence", arXiv:0912.3069, 2011.
- Riesselmann "Concept of ether in explaining forces", Inquiring Minds, Fermilab, 2008.
- Close, "Much ado about nothing", Nova, PBS/WGBH, 2012.
- On "historical examples of empirically successful theories that later turn out to be false", Okasha, Philosophy of Science (Oxford U P, 2002), p 65, concludes, "One that remains is the wave theory of light, first put forward by Christian Huygens in 1690. According to this theory, light consists of wave-like vibrations in an invisible medium called the ether, which was supposed to permeate the whole universe. (The rival to the wave theory was the particle theory of light, favoured by Newton, which held that light consists of very small particles emitted by the light source.) The wave theory was not widely accepted until the French physicist Auguste Fresnel formulated a mathematical version of the theory in 1815, and used it to predict some surprising new optical phenomena. Optical experiments confirmed Fresnel's predictions, convincing many 19th-century scientists that the wave theory of light must be true. But modern physics tells us that the theory is not true: there is no such thing as the ether, so light doesn't consist of vibrations in it. Again, we have an example of a false but empirically successful theory".
- Pigliucci, Answers for Aristotle (Basic Books, 2012), p 119: "But the antirealist will quickly point out that plenty of times in the past scientists have posited the existence of unobservables that were apparently necessary to explain a phenomenon, only to discover later on that such unobservables did not in fact exist. A classic case is the aether, a substance that was supposed by nineteenth-century physicists to permeate all space and make it possible for electromagnetic radiation (like light) to propagate. It was Einstein's special theory of relativity, proposed in 1905, that did away with the necessity of aether, and the concept has been relegated to the dustbin of scientific history ever since. The antirealists will relish pointing out that modern physics features a number of similarly unobservable entities, from quantum mechanical 'foam' to dark energy, and that the current crop of scientists seems just as confident about the latter two as their nineteenth-century counterparts were about aether".
- Wilczek, Lightness of Being (Basic Books, 2008), pp 78–80.
- Laughlin, A Different Universe (Basic Books, 2005), pp 120–21.
- Einstein, "Ether", Sidelights (Methuen, 1922), pp 14–18.
- Lorentz aether was at absolute rest—acting on matter but not acted on by matter. Replacing it and resembling Ernst Mach's aether, Einstein aether is spacetime itself—which is the gravitational field—receiving motion from a body and transmitting it to other bodies while propagating at light speed, waving. An unobservable, however, Einstein aether is not a privileged reference frame—is not to be assigned a state of absolute motion or absolute rest.
- Relativity theory comprises both special relativity (SR) and general relativity (GR). Holding for inertial reference frames, SR is as a limited case of GR, which holds for all reference frames, both inertial and accelerated. In GR, all motion—inertial, accelerated, or gravitational—is consequent of the geometry of 3D space stretched onto the 1D axis of time. By GR, no force distinguishes acceleration from inertia. Inertial motion is consequence simply of uniform geometry of spacetime, acceleration is consequence simply of nonuniform geometry of spacetime, and gravitation is simply acceleration.
- Laughlin, A Different Universe, (Basic Books, 2005), pp 120–21: "The word 'ether' has extremely negative connotations in theoretical physics because of its past association with opposition to relativity. This is unfortunate because, stripped of these connotations, it rather nicely captures the way most physicists actually think about the vacuum. ... Relativity actually says nothing about the existence or nonexistence of matter pervading the universe, only that any such matter must have relativistic symmetry. It turns out that such matter exists. About the time that relativity was becoming accepted, studies of radioactivity began showing that the empty vacuum of space had spectroscopic structure similar to that of ordinary quantum solids and fluids. Subsequent studies with large particle accelerators have now led us to understand that space is more like a piece of window glass than ideal Newtonian emptiness. It is filled with 'stuff' that is normally transparent but can be made visible by hitting it sufficiently hard to knock out a part. The modern concept of the vacuum of space, confirmed every day by experiment, is a relativistic ether. But we do not call it this because it is taboo".
- In Einstein's 4D spacetime, 3D space is stretched onto the 1D axis of time flow, which slows while space additionally contracts in the vicinity of mass or energy.
- Torretti, Philosophy of Physics (Cambridge U P, 1999), p 180.
- As an effective field theory, once adjusted to particular domains, Standard Model is predictively accurate until a certain, vast energy scale that is a cutoff, whereupon more fundamental phenomena—regulating the effective theory's modeled phenomena—would emerge. (Burgess & Moore, Standard Model, p xi; Wells, Effective Theories, pp 55–56).
- Torretti, Philosophy of Physics (Cambridge U P, 1999), p 396.
- Jegerlehner, "The Standard Model as a low-energy effective theory", arXiv:1304.7813: "We understand the SM as a low energy effective emergence of some unknown physical system—we may call it 'ether'—which is located at the Planck scale with the Planck length as a 'microscopic' length scale. Note that the cutoff, though very large, in any case is finite".
- Wilczek, Lightness of Being (Basic Books, 2008), ch 8 "The grid (persistence of ether)", p 73: "For natural philosophy, the most important lesson we learn from QCD is that what we perceive as empty space is in reality a powerful medium whose activity molds the world. Other developments in modern physics reinforce and enrich that lesson. Later, as we explore the current frontiers, we'll see how the concept of 'empty' space as a rich, dynamic medium empowers our best thinking about how to achieve the unification of forces".
- Mass–energy equivalence is formalized in the equation E=mc2.
- Einstein, "Ether", Sidelights (Methuen, 1922), p 13: "[A]ccording to the special theory of relativity, both matter and radiation are but special forms of distributed energy, ponderable mass losing its isolation and appearing as a special form of energy".
- Braibant, Giacomelli & Spurio, Particles and Fundamental Interactions (Springer, 2012), p 2: "Any particle can be created in collisions between two high energy particles thanks to a process of transformation of energy in mass".
- Brian Greene explained, "People often have the wrong image of what happens inside the LHC, and I am just as guilty as anyone of perpetuating it. The machine does not smash together particles to pulverise them and see what is inside. Rather, it collides them at extremely high energy. Since, by dint of Einstein's famous equation, E=mc2, energy and mass are one and the same, the combined energy of the collision can be converted into a mass, in other words, a particle, that is heavier than either of the colliding protons. The more energy is involved in the collision, the heavier the particles that might come into being" [Avent, "The Q&A", Economist, 2012].
- Kuhlmann, "Physicists debate", Sci Am, 2013.
- Whereas Newton's Principia inferred absolute space and absolute time, omitted an aether, and, by Newton's law of universal gravitation, formalized action at a distance—a supposed force of gravitation spanning the entire universe instantly—Newton's later work Optiks introduced an aether binding bodies' matter, yet denser outside bodies, and, not uniformly distributed across all space, in some locations condensed, whereby "aethereal spirits" mediate electricity, magnetism, and gravitation. (Whittaker, A History of Theories of Aether (Longmans, Green & Co: 1910), pp 17–18)
- Norton, "Causation as folk science", in Price & Corry, eds, Mature Causation, Physics, and the Constitution of Reality (Oxford U P, 2007), esp p 12.
- Fetzer, ch 3, in Fetzer, ed, Science, Explanation, and Rationality (Oxford U P, 2000), p 111.
- Explanandum and explanans
- Hypothetico-deductive model
- Models of scientific inquiry
- Philosophy of science
- Scientific method
Types of inference
Though discovery of causality is popularly thought science's aim, search for it was shunned by the Newtonian research program, even more Newtonian than was Isaac Newton. By now, most theoretical physicists infer that the four, known fundamental interactions would reduce to superstring theory, whereby atoms and molecules, after all, are energy vibrations holding mathematical, geometric forms. Given uncertainties of scientific realism, some conclude that the concept causality raises comprehensibility of scientific explanation and thus is key folk science, but compromises precision of scientific explanation and is dropped as a science matures. Even epidemiology is maturing to heed the severe difficulties with presumptions about causality. Covering law model is among Carl G Hempel's admired contributions to philosophy of science.
In 1905, from special relativity, Einstein deduced mass–energy equivalence, particles being variant forms of distributed energy, how particles colliding at vast speed experience that energy's transformation into mass, producing heavier particles, although physicists' talk promotes confusion. As "the contemporary locus of metaphysical research", QFTs pose particles not as existing individually, yet as excitation modes of fields, the particles and their masses being states of aether, apparently unifying all physical phenomena as the more fundamental causal reality, as long ago foreseen. Yet a quantum field is an intricate abstraction—a mathematical field—virtually inconceivable as a classical field's physical properties. Nature's deeper aspects, still unknown, might elude any possible field theory.
 By 1970, QED along with
Physicists have feared even mentioning aether, renamed vacuum, which—as such—is nonexistent. General philosophers of science commonly believe that aether, rather, is fictitious, "relegated to the dustbin of scientific history ever since" 1905 brought special relativity. Einstein was noncommittal to aether's nonexistence, simply said it superfluous. Abolishing Newtonian motion for electrodynamic primacy, however, Einstein inadvertently reinforced aether, and to explain motion was led back to aether in general relativity. Yet resistance to relativity theory became associated with earlier theories of aether, whose word and concept became taboo. Einstein explained special relativity's compatibility with an aether, but Einstein aether, too, was opposed. Objects became conceived as pinned directly on space and time by abstract geometric relations lacking ghostly or fluid medium.
Meeting in 1947, Freeman Dyson, Richard Feynman, Julian Schwinger, and Sin-Itiro Tomonaga soon introduced renormalization, a procedure converting QED to physics' most predictively precise theory, subsuming chemistry, optics, and statistical mechanics. QED thus won physicists' general acceptance. Paul Dirac criticized its need for renormalization as showing its unnaturalness, and called for an aether. In 1947, Willis Lamb had found unexpected motion of electron orbitals, shifted since the vacuum is not truly empty. Yet emptiness was catchy, abolishing aether conceptually, and physics proceeded ostensibly without it, even suppressing it. Meanwhile, "sickened by untidy math, most philosophers of physics tend to neglect QED".
In 1941, Richard Feynman introduced QM's path integral formalism, which if taken toward interpretation as a causal mechanical model clashes with Heisenberg's matrix formalism and with Schrödinger's wave formalism, although all three are empirically identical, sharing predictions. Next, working on QED, Feynman sought to model particles without fields and find the vacuum truly empty. As each known fundamental force is apparently an effect of a field, Feynman failed. Louis de Broglie's waveparticle duality had rendered atomism—indivisible particles in a void—untenable, and highlighted the very notion of discontinuous particles as selfcontradictory.
In 1925, Werner Heisenberg as well as Erwin Schrödinger independently formalized quantum mechanics (QM). Despite clashing explanations, the two theories made identical predictions. Paul Dirac's 1928 model of the electron was set to special relativity, launching QM into the first quantum field theory (QFT), quantum electrodynamics (QED). From it, Dirac interpreted and predicted the electron's antiparticle, soon discovered and termed positron, but the QED failed electrodynamics at high energies. Elsewhere and otherwise, strong nuclear force and weak nuclear force were discovered.
Finding the luminiferous aether a useless hypothesis, Einstein in 1905 a priori unified all inertial reference frames to state special principle of relativity, which, by omitting aether, converted space and time into relative phenomena whose relativity aligned electrodynamics with the Newtonian principle Galilean relativity or invariance. Originally epistemic or instrumental, this was interpreted as ontic or realist—that is, a causal mechanical explanation—and the principle became a theory, refuting Newtonian gravitation. By predictive success in 1919, general relativity apparently overthrew Newton's theory, a revolution in science resisted by many yet fulfilled around 1930.
In 1905, via statistical mechanics, Albert Einstein predicted the phenomenon Brownian motion—unexplained since reported in 1827 by botanist Robert Brown. Soon, most physicists accepted that atoms and molecules were unobservable yet real. Also in 1905, Einstein explained the electromagnetic field's energy as distributed in particles, doubted until this helped resolve atomic theory in the 1910s and 1920s. Meanwhile, all known physical phenomena were gravitational or electromagnetic, whose two theories misaligned. Yet belief in aether as the source of all physical phenomena was virtually unanimous. At experimental paradoxes, physicists modified the aether's hypothetical properties.
Through lawlike explanation, fundamental physics—often perceived as fundamental science—has proceeded through intertheory relation and theory reduction, thereby resolving experimental paradoxes to great historical success, resembling covering law model. In early 20th century, Ernst Mach as well as Wilhelm Ostwald had resisted Ludwig Boltzmann's reduction of thermodynamics—and thereby Boyle's law—to statistical mechanics partly because it rested on kinetic theory of gas, hinging on atomic/molecular theory of matter. Mach as well as Ostwald viewed matter as a variant of energy, and molecules as mathematical illusions, as even Boltzmann thought possible.
Scientific explanations increasingly pose not determinism's universal laws, but probabilism's chance, ceteris paribus laws. Smoking's contribution to lung cancer fails even the inductive-statistical model (IS model), requiring probability over 0.5 (50%). (Probability standardly ranges from 0 (0%) to 1 (100%).) An applied science that applies statistics seeking associations between events, epidemiology cannot show causality, but consistently found higher incidence of lung cancer in smokers versus otherwise similar nonsmokers, although the proportion of smokers who develop lung cancer is modest. Versus nonsmokers, however, smokers as a group showed over 20 times the risk of lung cancer, and in conjunction with basic research, consensus followed that smoking had been scientifically explained as a cause of lung cancer, responsible for some cases that without smoking would not have occurred, a probabilistic counterfactual causality.
Many philosophers have concluded that causality is integral to scientific explanation. DN model offers a necessary condition of a causal explanation—successful prediction—but not sufficient conditions of causal explanation, as a universal regularity can include spurious relations or simple correlations, for instance Z always following Y, but not Z because of Y, instead Y and then Z as an effect of X. By relating temperature, pressure, and volume of gas within a container, Boyle's law permits prediction of an unknown variable—volume, pressure, or temperature—but does not explain why to expect that unless one adds, perhaps, the kinetic theory of gases.
By DN model, if one asks, "Why is that shadow 20 feet long?", another can answer, "Because that flagpole is 15 feet tall, the Sun is at x angle, and laws of electromagnetism". Yet by problem of symmetry, if one instead asked, "Why is that flagpole 15 feet tall?", another could answer, "Because that shadow is 20 feet long, the Sun is at x angle, and laws of electromagnetism", likewise a deduction from observed conditions and scientific laws, but an answer clearly incorrect. By the problem of irrelevance, if one asks, "Why did that man not get pregnant?", one could in part answer, among the explanans, "Because he took birth control pills"—if he factually took them, and the law of their preventing pregnancy—as covering law model poses no restriction to bar that observation from the explanans.
Covering law model reflects neopositivism's vision of empirical science, a vision interpreting or presuming unity of science, whereby all empirical sciences are either fundamental science—that is, fundamental physics—or are special sciences, whether astrophysics, chemistry, biology, geology, psychology, economics, and so on. All special sciences would network via covering law model. And by stating boundary conditions while supplying bridge laws, any special law would reduce to a lower special law, ultimately reducing—theoretically although generally not practically—to fundamental science. (Boundary conditions are specified conditions whereby the phenomena of interest occur. Bridge laws translate terms in one science to terms in another science.)
Discarding ontic commitments, including causality per se, DN model permits a theory's laws to be reduced to—that is, subsumed by—a more fundamental theory's laws. The higher theory's laws are explained in DN model by the lower theory's laws. Thus, the epistemic success of Newtonian theory's law of universal gravitation is reduced to—thus explained by—Einstein's general theory of relativity, although Einstein's discards Newton's ontic claim that universal gravitation's epistemic success predicting Kepler's laws of planetary motion is through a causal mechanism of a straightly attractive force instantly traversing absolute space despite absolute time.
Natural laws, so called, are statements of humans' observations, thus are epistemological—concerning human knowledge—the epistemic. Causal mechanisms and structures existing putatively independently of minds exist, or would exist, in the natural world's structure itself, and thus are ontological, the ontic. Blurring epistemic with ontic—as by incautiously presuming a natural law to refer to a causal mechanism, or to trace structures realistically during unobserved transitions, or to be true regularities always unvarying—tends to generate a category mistake.
As theory of knowledge, epistemology differs from ontology, which is a subbranch of metaphysics, theory of reality. Ontology poses which categories of being—what sorts of things exist—and so, although a scientific theory's ontological commitment can be modified in light of experience, an ontological commitment inevitably precedes empirical inquiry.
Salmon introduced causal mechanical explanation, never clarifying how it proceeds, yet reviving philosophers' interest in such. Via shortcomings of Hempel's inductive-statistical model (IS model), Salmon introduced statistical-relevance model (SR model). Although DN model remained an idealized form of scientific explanation, especially in applied sciences, most philosophers of science consider DN model flawed by excluding many types of explanations generally accepted as scientific.
In 1948, when explicating DN model and stating scientific explanation's semiformal conditions of adequacy, Hempel and Oppenheim acknowledged redundancy of the third, empirical content, implied by the other three—derivability, lawlikeness, and truth. In the early 1980s, upon widespread view that causality ensures the explanans' relevance, Wesley Salmon called for returning cause to because, and along with James Fetzer helped replace CA3 empirical content with CA3' strict maximal specificity.
In the 1940s, filling the vast observational gap between cytology and nucleus. Launched in the late 1930s, the molecular biology research program cracked a genetic code in the early 1960s and then converged with cell biology as cell and molecular biology, its breakthroughs and discoveries defying DN model by arriving in quest not of lawlike explanation but of causal mechanisms. Biology became a new model of science, while special sciences were no longer thought defective by lacking universal laws, as borne by physics.
Amid failure of neopositivism's fundamental tenets, Hempel in 1965 abandoned verificationism, signaling neopositivism's demise. From 1930 onward, Karl Popper had refuted any positivism by asserting falsificationism, which Popper claimed had killed positivism, although, paradoxically, Popper was commonly mistaken for a positivist. Even Popper's 1934 book embraces DN model, widely accepted as the model of scientific explanation for as long as physics remained the model of science examined by philosophers of science.