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In modern logic, a proposition or ansatz is what is asserted as the result of uttering a sentence. In other words, it is the meaning of the sentence, rather than the sentence itself. Different sentences can express the same proposition, if they have the same meaning. A proposition is sometimes called a closed sentence, to distinguish it from an open sentence, or predicate.

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 propositionss, 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

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.