THE CONCEPT OF PROPOSITION
In logic and philosophy, the term proposition, from the word "proposal" refers to both, "content" or "meaning" of a meaningful declarative sentence or the pattern of symbols, marks, or sounds that make up a meaningful declarative sentence. The meaning of a proposition includes that it has the quality or property of being either true or false, and as such propositions are called truth bearers. The existence of propositions in the abstract sense, as well as the existence of "meanings", is disputed by some philosophers. Where the concept of a "meaning" is admitted, its nature is controversial. In earlier texts writers have not always made it sufficiently clear whether they are using the term proposition in sense of the words or the "meaning" expressed by the words. To avoid the controversies and ontological implications, the term sentence is often now used instead of proposition to refer to just those strings of symbols that are truth bearers, being either true or false under an interpretation.
Relation to the Mind
In relation to the mind, propositions are discussed primarily as they fit into propositional attitudes. Propositional attitudes are simply attitudes characteristic of folk psychology i.e. belief, desire, etc. that one can take toward a proposition. E.g. 'It is raining', 'snow is white', etc. In English, propositions usually follow folk psychological attitudes by a "that clause" e.g. "Jane believes that it is raining". In philosophy of mind and psychology, mental states are often taken to primarily consist in propositional attitudes. The propositions are usually said to be the "mental content" of the attitude. For example, if Jane has a mental state of believing that it is raining, her mental content is the proposition 'it is raining'. Furthermore, since such mental states are about something, they are said to be intentional mental states. Philosophical debates surrounding propositions as they relate to propositional attitudes have also recently centered on whether they are internal or external to the agent or whether they are mind-dependent or mind-independent entities.
Treatment in Logic
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." In Mathematical Logic, propositions, also called "propositional formulas" or "statement forms", are statements that do not contain quantifiers. They are composed of well-formed formulas consisting entirely of atomic formulas, the five logical connectives, and symbols of grouping. Propositional logic is one of the few areas of mathematics that is totally solved, in the sense that it has been proven internally consistent, every theorem is true, and every true statement can be proved. The most common extension of propositional logic is called predicate logic, which adds variables and quantifiers.
Objections to Propositions
Two meaningful declarative sentences express the same proposition if and only if they mean the same thing, thus defining proposition in terms of synonymy. For example, "Snow is white" in English and "Schnee ist weib" in German are different sentences, but they say the same thing, so they express the same proposition. Two meaningful declarative sentence-tokens express the same proposition if and only if they mean the same thing. Unfortunately, the above definition has the result that two sentences or sentence-tokens which have the same meaning and thus express the same proposition could have different truth-values, e.g. "I am Simon" said by Simon and said by John Smith; and e.g. "It is Wednesday" said on a Wednesday and on a Thursday.
In mathematical logic, this problem is solved with quantifiers. Both sentences are predicates, not propositions, because "I" and "It" are variables, and predicates only have a truth value when they are quantified. "For all days, it is Wednesday." is false. "There exist a day, such that it is Wednesday." is true. A number of philosophers and linguists claim that all definitions of a proposition are too vague to be useful. For them, it is just a misleading concept that should be removed from philosophy and semantics.
No comments:
Post a Comment