Proposition

:This article documents the term proposition as it is used in logic. For other usages see proposition (disambiguation).

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Proposition is a term used in logic to describe the content of assertions. An assertion is content which may be taken as being true or false. Assertions are non-linguistic abstractions from the linguistic sentences that constitute an assertion. The nature of propositions is highly controversial amongst philosophers, many of whom are skeptical about the existence of propositions. Many logicians prefer to avoid use of the term proposition in favour of using sentences.

Related Topics:
Logic - Assertion

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Different sentences may thus express the same proposition when they both have the same meaning. For example, Snow is white (in English) and Schnee ist weiss (in German) are different sentences, but both say the same thing, namely, that snow is white. Hence they express the same proposition. Two different sentences in the same language may also express the same proposition. For example, Tiny crystals of frozen water precipitation are white is in English, but is said to be the same proposition by virtue of the definition of "snow".

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The usual convention for naming propositions is to create a noun phrase by prefixing the word that to any sentence which expresses the proposition in question. Thus, that Jones is a bachelor is the proposition expressed by the sentence "Jones is a bachelor".

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Two other logical uses bear note: In Aristotelian logic a proposition is a particular kind of sentence: one which affirms or denies a predicate of a subject. Aristotelian propositions take forms like All men are mortal and Socrates is a man. Propositional logic is so named because its atomic elements the expressions of complete propositions; they are often simply called propositions. The sentence A and B expresses both proposition A and proposition B. Both of these uses treat a proposition simply as a sentence (albeit of a certain kind). This usage is increasingly non-standard, and will not be used in the rest of this article.

Related Topics:
Aristotelian logic - Predicate - Subject - Propositional logic

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Often propositions are related to closed sentences, to distinguish them from what is expressed by an open sentence, or predicate. In this sense, propositions are statements that are either true or false. This conception of a proposition was supported by the philosophical school of logical positivism.

Related Topics:
Predicate - True or false - Logical positivism

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Some philosophers, such as John Searle, hold that other kinds of speech or actions also assert propositions. Yes-no questions are an inquiry into a proposition's truth value. Traffic signs express propositions without using speech or written language. It is also possible to use a declarative sentence to express a proposition without asserting it, as when a teacher asks a student to comment on a quote; the quote is a proposition (that is, it has a meaning) but the teacher is not asserting it. The second paragraph of this article expressed the proposition that snow is white without asserting it (i.e. claiming snow is white).

Related Topics:
John Searle - Question - Traffic sign

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Propositions are usually spoken of as the content of beliefs and similar representative thoughts. They can also be the object of other attitudes like desire, preference, intention, inquiry, as "I desire that I have a new car," or "I wonder whether it will snow" (or, whether it is the case that it will snow). Desire, belief, and so on, are thus called propositional attitudes when they take this sort of somtent.

Related Topics:
Content - Beliefs - Representative thought - Desire - Preference - Intention - Inquiry

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