In modern philosophy, logic and linguistics, a proposition is what is asserted as the result of uttering a declarative sentence. In other words, it is the meaning of the sentence, rather than the sentence itself. Different sentences, even in different languages, express the same proposition when they have the same meaning.

Sometimes one says that a proposition is what is expressed by a closed sentence, to distinguish it from what is expressed by an open sentence, or predicate.

Not only declarative sentences express propositions. Yes-no questions also express propositions, questioning them. The utterance of declarative sentences usually asserts propositions, but some declarative sentences might express propositions without asserting them, as when a teacher asks the students to comment some saying. Questions and assertions are kinds of speech acts. Searle and some other authors claim that every speech act has a propositional content.

Non verbal signs can also express propositions. Warning and information traffic signs do it. It is useful to keep in mind that not only sentences express propositions, in order not to think that they are alike. If propositions have a structure, it is not equivalent to the syntactic structure of a sentence.

Propositions are usually said to be the object or content of beliefs, disbeliefs and some thoughts (representative thoughts). Some authors, like Davidson, also affirm that propositions are the object of other attitudes, like desire and wanting. Desire, belief etc. are then called propositional attitudes.

Modal operators like possibility and impossibility have propositions in their scope. What is possible or impossible is not the event or fact, but the proposition related to them.

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Propositions are true or false. That is the feature that distinguishes them from other meanings or thoughts, like norms. Propositions are truthbearers, like some sentences or beliefs. Events, facts or states of affairs (which in philosophy are not synonyms) are truthmakers. This distinction stands on the much debated correspondence theory of truth.

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Whether propositions are real entities, and if so of what sort (e.g., Platonic abstracta), is a matter of philosophical dispute.

Anyway, propositions by definition are not physical entities. Therefore philosophers discuss whether propositions do objectively exist in a Platonic realm or they are mere abstractions or something in between. If propositions are mere abstractions, they do not exist, but it is adequate to talk about them as if they existed. Otherwise there will be the danger of reductionism.

Many philosophers and linguists simply do not accept propositions. For them, this is just a misleading concept that should be banned from philosophy and semantics.

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In Aristotelian logic a proposition is a particular kind of sentence, one which affirms or denies a predicate of a subject, and thus asserts something true or false. Propositions fall unto three classes. Universal propositions, such as "all men are mortal" affirm or deny the predicate mortal of the "whole of" their subject, i.e. the entire class of things that the subject applies to. Particular propositions, such as "some men are mortal" affirm or deny the predicate of only part of the subject. Singular propositions, such as "Socrates is a man" present a difficulty. Usually they were regarded as a universal proposition, since they can only be true of a single object, and thus true of all the objects (one) they possibly can be true of. On the other hand, "they are in truth the most limited kind of particular propositions".

See also: symbolic logic, truthmaker, propositional logic

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In many U.S. states, a proposition is a ballot measure consisting of a statute or constitutional amendment "proposed" to the voters for their approval. It can take the form of an initiative or referendum. For example, see the list of California ballot propositions.

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Proposition is also a name given, in debates, to the team which supports and tries to prove a motion.

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