Carl Gustav Hempel

Life and Career

Carl Gustav Hempel (1905–1997) was a leading figure of logical empiricism and one of the most influential philosophers of science in the 20th century. Born in Oranienburg, near Berlin, he studied mathematics, physics, and philosophy at universities in Göttingen, Heidelberg, and Berlin. In Berlin he encountered Hans Reichenbach and the Berlin Circle, and in 1929 he participated in the founding conference of the Vienna Circle, meeting key logical positivists such as Rudolf Carnap and Moritz Schlick.

Hempel completed his doctorate in 1934 under Reichenbach with a dissertation on probability and induction. As the political situation in Germany deteriorated under National Socialism and anti‑Jewish policies intensified, Hempel—himself not Jewish but closely associated with many Jewish colleagues—emigrated, first to Belgium and then, in 1937, to the United States.

In America he worked with Carnap at the University of Chicago and then taught at the City College of New York, Queens College, and Yale University. In 1955 he joined Princeton University, where he became a central figure in postwar analytic philosophy and trained generations of philosophers. Hempel retired from Princeton in 1973 but continued to teach at the University of Pittsburgh, another major center for philosophy of science, before returning to Princeton. He died in Princeton, New Jersey, in 1997.

Logical Empiricism and Method

Hempel’s work is deeply rooted in logical empiricism, a movement seeking to combine empiricist ideas about knowledge with the tools of modern logic. He held that philosophical problems about science should be addressed by:

• Formulating scientific statements in a precise, formal language
• Analyzing the logical structure of theories, explanations, and confirmations
• Maintaining that meaningful statements must, at least in principle, be connected to empirical observation

Hempel was particularly concerned with the status of theoretical terms—such as “electron” or “gene”—that are not directly observable. With Paul Oppenheim he explored how such terms could be introduced via theoretical explanations and related to observation by logical and empirical links. His textbook Philosophy of Natural Science (1966) presented these themes in an accessible and influential form, becoming a standard introduction to the field.

A hallmark of Hempel’s method is his insistence on the symmetry of explanation and prediction: logically, an explanation of an event and a prediction of a future event have the same structure, differing only in whether the event is known beforehand. This symmetry shaped his account of scientific rationality and the role of laws in science.

Hempel also contributed to confirmation theory, attempting to clarify what it means for evidence to support or confirm a hypothesis. His discussions of paradoxes of confirmation—most notably Hempel’s paradox of the ravens—sought to test and refine intuitive ideas about inductive support using formal tools.

Scientific Explanation and the DN Model

Hempel is best known for his analysis of scientific explanation, especially the deductive‑nomological (DN) model, sometimes called the “covering‑law model.” According to this account, a satisfactory scientific explanation of a particular event has the form of a deductive argument:

• The explanans consists of
  • at least one lawlike generalization (a law of nature), and
  • relevant initial conditions or particular facts;
• The explanandum is the statement describing the event or regularity to be explained;
• The explanandum must follow logically from the explanans.

On this view, to explain why a piece of metal expanded when heated, one deduces that it must expand from general laws about thermal expansion plus facts about its being heated. The same structure underlies scientific prediction: given the law and conditions, one can derive what will happen.

For explanations involving probabilistic laws, Hempel developed the inductive‑statistical (IS) model, in which explanations show that the explanandum event had a high probability given certain statistical laws and conditions, rather than following deductively.

These models aimed to capture key scientific ideals:

• Lawlikeness: Explanations must appeal to genuine laws, not accidental regularities.
• Objectivity and generality: Explanations are not narrative stories but logical relations among statements.
• Unity of science: The same structural features of explanation apply across different scientific domains.

Hempel’s models became central reference points in discussions of scientific explanation, inspiring extensive debate about the roles of laws, causation, and probability in science.

Legacy and Criticisms

Hempel’s work shaped mid‑century analytic philosophy of science, establishing topics—such as explanation, confirmation, and theory structure—that remain central. His careful, formally rigorous style influenced both methodology and pedagogy, and his writings continue to be widely taught.

At the same time, his views provoked substantial criticism. Some philosophers argued that the DN model allowed “explanations” that seemed intuitively unsatisfactory. For instance, laws about atmospheric refraction can be used to “explain” why a flagpole casts a certain shadow, but, by reversing the geometry, one could deductively “explain” the height of the flagpole from the length of its shadow and the same law. Critics contended that the DN model alone cannot distinguish genuinely explanatory from merely derivable relationships, nor adequately capture causal direction.

Others held that scientific explanation often involves mechanisms, models, and idealizations in ways that are not easily reconstructed as simple law‑plus‑conditions arguments. Philosophers of biology and the social sciences, for example, argued that not all explanatory success depends on strict laws of nature, challenging the centrality of laws in Hempel’s account.

In confirmation theory, Hempel’s paradox of the ravens—the idea that observing a green apple seems, under some logical analyses, to confirm the hypothesis “All ravens are black”—raised doubts about purely formal treatments of inductive support. Subsequent Bayesian and model‑based approaches sought to incorporate background knowledge and degrees of belief in ways that go beyond Hempel’s original framework.

Despite these criticisms, Hempel’s contributions are widely regarded as foundational. Proponents see his work as having clarified what is at stake in accounts of explanation and confirmation, even where later theories depart from his positions. Critics maintain that the limitations of logical empiricism—its difficulties with theoretical change, meaning holism, and scientific practice—reveal the need for more historically and materially grounded accounts of science.

Hempel’s legacy lies less in a set of final doctrines than in a program of analysis: the attempt to understand scientific reasoning through the interplay of logic, empirical content, and conceptual clarity. His work remains a central point of reference for discussions of how and why science explains.