---
title: "Deductive-nomological model"
chunk: 2/6
source: "https://en.wikipedia.org/wiki/Deductive-nomological_model"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T03:43:33.815064+00:00"
instance: "kb-cron"
---

== Growth ==
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.
Hempel held natural laws—empirically confirmed regularities—as satisfactory, and if included realistically to approximate causality.  In later articles, Hempel defended DN model and proposed probabilistic explanation by inductive-statistical model (IS model).  DN model and IS model—whereby the probability must be high, such as at least 50%—together form covering law model, as named by a critic, William Dray.  Derivation of statistical laws from other statistical laws goes to the deductive-statistical model (DS model).  Georg Henrik von Wright, another critic, named the totality subsumption theory.

== Decline ==
Amid failure of neopositivism's fundamental tenets, Hempel in 1965 abandoned verificationism, signaling neopositivism's demise. From 1930 onward, Karl Popper attacked 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.
In the 1940s, filling the vast observational gap between cytology and biochemistry, cell biology arose and established existence of cell organelles besides the 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.
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.
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.

== Strengths ==
As theory of knowledge, epistemology differs from ontology, which is a subbranch of metaphysics, theory of reality.  Ontology proposes 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.
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.
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—Albert 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.
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.)