In This Article Expand or collapse the "in this article" section Theoretical Terms in Science

  • Introduction
  • General Overviews
  • Historical Roots
  • Formal Semantics
  • Theory-Observation Distinction
  • Doubts about the Theory-Observation Distinction
  • Epistemology
  • Doubts about Logical Empiricist Epistemology

Philosophy Theoretical Terms in Science
Holger Andreas
  • LAST REVIEWED: 26 February 2020
  • LAST MODIFIED: 26 February 2020
  • DOI: 10.1093/obo/9780195396577-0400


What is a theoretical term? This question can be answered in at least two different ways. First, a theoretical term is simply a non-observational term. Second, a theoretical term is one whose meaning depends on the axioms of a scientific theory. According to the first explanation, a theoretical term cannot be applied using just unaided perception, without drawing inferences. This explanation defines the notion of theoreticity merely as the absence of observability. The second explanation, by contrast, has the virtue of giving a positive characterization of the notion of theoreticity. Both explanations stand in the need of further elaboration. If we characterize theoretical terms by non-observability, we need to explain what an observational term is. There is no consensus in the literature as to whether and, if so, to what extent it is feasible to draw the theory-observation distinction. On the one hand, critics of the theory-observation distinction have often attacked only weak proposals of how to draw the distinction in question. On the other hand, the extreme skepticism by Thomas S. Kuhn, Paul K. Feyerabend, and Norwood R. Hanson concerning the distinction is increasingly losing consensus among contemporary philosophers of science. This is evidenced, for example, by attempts at exploiting the formal semantics of theoretical terms in one version of structural realism. If we explain the notion of a theoretical term by way of semantic dependency upon a scientific theory, we need to give an account of this semantic relation. How does a theory determine the meaning of a theoretical term? What, if any, are the differences between theoretical terms and defined terms? How can we distinguish, in a sensible way, between the synthetic assertions of a scientific theory about the world and meaning postulates determining the meaning of theoretical terms? Various formal semantics of theoretical terms have been devised in order to answer these questions. Notably, the idea that the meaning of a theoretical term is determined by a scientific theory, or a set of such theories, has already been expressed by Pierre Duhem and Henrie Poincaré. The theory-observation distinction can be applied to syntactic and semantic entities. Thus, we can speak of theoretical terms and theoretical concepts. Moreover, we can speak of theoretical entities, in the sense of specific objects that are the referents of theoretical concepts. Philosophical research on theoreticity concerns syntactic aspects inasmuch as semantic aspects of theoreticity.

General Overviews

Andreas 2017 gives a comprehensive overview of the key questions and key results concerning theoretical terms in modern philosophy of science. Carnap 1966 gives an accessible introduction to theoretical terms and theoretical concepts. Przełęcki 1969 is a concise treatise on scientific theories, written from the perspective of a syntactic approach to such theories. Notably, Przełęcki 1969 explains various formal semantics of theoretical terms, without thereby becoming overly technical. Tuomela 1973 is a self-contained investigation that sets out to solve Hempel’s Theoretician’s Dilemma: on the one hand, (1) logical empiricists want to spell out the semantics of theoretical terms in terms of propositions of an observation language. On the other hand, (2) theoretical terms are expected to have some genuine virtues that observational terms are lacking. At least on a strict reading of (1), a theoretical term is perfectly meaningful only if any assertion with an occurrence of the term can be translated into an observation language. Now, if all theoretical terms are perfectly meaningful in this sense, we could dispense with theoretical terms altogether, which contradicts (2). This dilemma is certainly central to the overall semantics of theoretical concepts. Hence, Tuomela’s book gives a good overview of our topic and the logical empiricist’s literature on theoretical terms. Suppe 1974 reviews a great deal of logical empiricist literature that leads to Carnap’s mature account of theoretical terms and scientific theories. Van Benthem 1982 is recommended for a more technical review of various semantics of theoretical terms.

  • Andreas, Holger. Theoretical terms in science. In The Stanford Encyclopedia of Philosophy. Edited by Edward N. Zalta. Stanford, CA: Stanford University Press, 2017.

    Andreas gives a comprehensive overview of the key questions and results concerning theoretical terms. The entry focuses on the theory-observation distinction and the formal semantics of theoretical terms.

  • Carnap, Rudolf. Philosophical Foundations of Physics: An Introduction to the Philosophy of Science. New York: Basic Books, 1966.

    Chapters 23 to 26 of this book give an accessible introduction to theoretical concepts. Among other things, Carnap gives a straightforward explanation of the theory-observation distinction.

  • Przełęcki, Marian. The Logic of Empirical Theories. London: Routledge & Kegan Paul, 1969.

    This is a concise investigation of scientific theories. It is written from the perspective of the syntactic approach to such theories but also exploits the tools of model-theoretic semantics. Przełęcki explains in greater detail various formal semantics of theoretical terms.

  • Suppe, Frederick. “The Search for a Philosophical Understanding of Scientific Theories.” In The Structure of Scientific Theories. Edited by Frederick Suppe, 3–232. Urbana: University of Illinois Press, 1974.

    This is a detailed historical and systematic account of what was termed the “Received View of Scientific Theories” at that time. This view is closely associated with the work of Carnap, Hempel, and other logical empiricists. Suppe reviews the key topics of the received view: theoretical terms, theory-observation distinction, cognitive significance, partial interpretation. This review is also useful as an overview of the most influential criticisms of a logical empiricist account of scientific theories at that time.

  • Tuomela, Raimo. Theoretical Concepts. Berlin: Springer, 1973.

    DOI: 10.1007/978-3-7091-7106-6

    Tuomela sets out to solve Hempel’s Theoretician’s Dilemma. Unlike many other investigations of theoreticity, the focus is on theoretical terms in the social and behavioral sciences.

  • Van Benthem, Johan. “The Logical Study of Science.” Synthese 51 (1982): 431–472.

    DOI: 10.1007/BF00485263

    Van Benthem gives a more technical overview of various logical analyses of scientific theories. All of these are driven by two assumptions. First, the language of a scientific theory can be divided into two levels. One of the two levels is more elementary, concrete, and closer to observation, while the other is more abstract. Second, such a division leads to new insights about the nature of scientific theorizing.

back to top

Users without a subscription are not able to see the full content on this page. Please subscribe or login.

How to Subscribe

Oxford Bibliographies Online is available by subscription and perpetual access to institutions. For more information or to contact an Oxford Sales Representative click here.