Philosophy Propositions
Jeffrey C. King
  • LAST REVIEWED: 24 July 2013
  • LAST MODIFIED: 24 July 2013
  • DOI: 10.1093/obo/9780195396577-0212


Though there is significant disagreement among philosophers as to the nature of propositions, there is significant agreement as to what philosophical roles propositions are supposed to play. Hence, it is best to explain what propositions are by saying what they are supposed to do. It seems clear that sentences in some sense encode information and that two sentences of the same or different languages may encode the same piece of information. Perhaps “Snow is white” and “Schnee ist weiss” is an example of the latter. If we posit the existence of propositions, they can be identified with pieces of information encoded by sentences; and we can say that the above two sentences express the same proposition. Sentences are true or false in virtue of encoding the information, and hence expressing the propositions, that they do. Hence, propositions are sometimes called the primary bearers of truth and falsity, since sentences are derivatively true or false in virtue of expressing the proposition that they do. Propositions are also thought to be the bearers of modal properties, like being necessary or possible. Further, thinking agents are thought to bear various cognitive relations to propositions: they are the things we believe, doubt, assume, and deny. Related to this latter point, and turning now more to philosophy of language, sentences like “Frege believes that arithmetic reduces to logic” assert that there is a relation, believing, between Frege and the proposition that arithmetic reduces to logic, which is designated by “that arithmetic reduces to logic.” Propositions are also thought to be designated by other expressions, such as “Goldbach’s conjecture” and “what John just said.” Hence, sentences like “What John said entails Goldbach’s conjecture” and others suggest that propositions can stand in relation to each other (entailment) and possess a variety of properties. In addition, many believe that perceptual experiences have accuracy conditions: they can represent the way the world is around us accurately or inaccurately. Many think that the reason this is so is that perceptual experiences have as their contents propositions. However, even among those who agree on this, there is significant disagreement about the nature of the propositions that are the contents of perceptual experience and whether they can be expressed by sentences of natural languages. Finally, current thinking about propositions was very much influenced by the views of Gottlob Frege and Bertrand Russell in the late 19th and early 20th centuries.

Frege’s Theory of Thoughts

The German mathematician and philosopher Gottlob Frege developed a theory of thoughts, which he took to be expressed by sentences of natural languages and which were true or false. Frege took sentences to be true or false in virtue of expressing true or false thoughts. Thoughts for Frege were believed, doubted, and so on. So Frege’s thoughts play many of the roles philosophers take propositions to play. For any simple or complex linguistic expression, including sentences, Frege distinguished the sense of the expression from its reference. The sense of an expression determines its referent. The sense of the name “Aristotle” could be thought of as a condition Aristotle uniquely satisfies, like being Plato’s greatest student. This sense determines the referent of the name (Aristotle himself) since the referent uniquely satisfies the sense. The referent of a predicate like “is smart” Frege took to be a function from objects to truth-values. In this case, it maps an object o to true iff o is smart; and to false iff o isn’t smart. Frege called functions from objects to truth-values concepts. The sense of such a predicate is a descriptive condition that the function just described uniquely satisfies. Frege thought that the sense of a one-place predicate like “is smart” is incomplete or in need of saturation in just the way the predicate “is smart” itself feels incomplete. Now Frege appears to say that the sense of the sentence “Frege is smart” is built up out of the senses of “Frege” and “is smart.” Frege thought the sense of “Frege” and the sense of “is smart” are held together in the sense of the sentence “Frege is smart” by the “whole,” “complete” sense of “Frege” saturating the incomplete sense of “is smart.” The sense of the sentence “Frege is smart” just is a thought. In general, the senses of complete declarative sentences are thoughts (ignoring contextually sensitive expressions). The referent of a sentence, determined by its sense/thought, is a truth-value: the true or the false. Finally, Frege held that thoughts, and senses generally, exist independently of minds and language in what he famously called the third realm. By this he meant that thoughts exist neither in the physical world nor only in our minds. Frege 1963, Frege 1997a, Frege 1997b, Frege 1997c, and Frege 1997d are central sources of the view just sketched. Burge 1979, Dummett 1981, and Heck and May 2011 are important secondary works on Frege.

  • Burge, Tyler. “Sinning against Frege.” Philosophical Review 88.3 (1979): 398–432.

    DOI: 10.2307/2184957

    Influential reexamination of the Fregean notion of sense. Available online for purchase or by subscription.

  • Dummett, Michael. The Interpretation of Frege’s Philosophy. Cambridge, MA: Harvard University Press, 1981.

    Comprehensive critical interpretation of Frege’s philosophy of language.

  • Frege, Gottlob. “Compound Thoughts.” Mind 72.285 (1963): 1–17.

    DOI: 10.1093/mind/LXXII.285.1

    Frege’s best discussion of the internal structure of thoughts and complex thoughts (e.g., thoughts expressed by sentences containing “and,” “or,” etc.). English translation of Logische Untersuchungen. Dritter Teil: Gedankengefüge, first published in 1923. Available online for purchase or by subscription.

  • Frege, Gottlob. “On Sinn and Bedeutung.” In The Frege Reader. Edited by Michael Beaney, 151–171. Oxford: Blackwell, 1997a.

    Central text in which Frege makes the distinction between sense and reference. English translation of Über Sinn und Bedeutung, first published in 1892.

  • Frege, Gottlob. “Function and Concept.” In The Frege Reader. Edited by Michael Beaney, 130–148. Oxford: Blackwell, 1997b.

    Central text in which Frege makes the distinction between concept and object. Also contains one of his best explanations of his notion of concept. English translation of Funktion und Begriff, first published in 1891.

  • Frege, Gottlob. “On Concept and Object.” In The Frege Reader. Edited by Michael Beaney, 181–193. Oxford: Blackwell, 1997c.

    Central discussion of Frege’s notions of concept and object. Raises the famous problem of the concept “horse.” English translation of Über Begriff und Gegenstand, first published in 1892.

  • Frege, Gottlob. “Thought.” In The Frege Reader. Edited by Michael Beaney, 325–345. Oxford: Blackwell, 1997d.

    Frege’s most explicit discussion of thoughts and their properties. English translation of Der Gedanke, first published in 1918.

  • Heck, Richard G., Jr., and Robert May. “The Composition of Thoughts.” Nous 45.1 (2011): 126–166.

    DOI: 10.1111/j.1468-0068.2010.00769.x

    Critical discussion of Fregean thoughts and the respect in which they have internal structure. Available online for purchase or by subscription.

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