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Sentences are then built up out of atomic sentences by applying connectives and quantifiers. A set of sentences is called a theory; thus, individual sentences may be called theorems. To properly evaluate the truth (or falsehood) of a sentence, one must make reference to an interpretation of the theory.
In logic, a logical connective (also called a logical operator, sentential connective, or sentential operator) is a logical constant. Connectives can be used to connect logical formulas. Connectives can be used to connect logical formulas.
In mathematical logic, a propositional variable (also called a sentence letter, [1] sentential variable, or sentential letter) is an input variable (that can either be true or false) of a truth function. Propositional variables are the basic building-blocks of propositional formulas, used in propositional logic and higher-order logics.
For example, the connective "and" is truth-functional since a sentence like "Apples are fruits and carrots are vegetables" is true if, and only if, each of its sub-sentences "apples are fruits" and "carrots are vegetables" is true, and it is false otherwise. Some connectives of a natural language, such as English, are not truth-functional.
[2] [34] Sentential connectives are any linguistic particles that bind sentences to create a new compound sentence, [2] [34] or that inflect a single sentence to create a new sentence. [2] A logical connective, or propositional connective, is a kind of sentential connective with the characteristic feature that, when the original sentences it ...
The corresponding logical symbols are "", "", [6] and , [10] and sometimes "iff".These are usually treated as equivalent. However, some texts of mathematical logic (particularly those on first-order logic, rather than propositional logic) make a distinction between these, in which the first, ↔, is used as a symbol in logic formulas, while ⇔ is used in reasoning about those logic formulas ...
For example, modus ponens is a rule of inference according to which all arguments of the form "(1) p, (2) if p then q, (3) therefore q" are valid, independent of what the terms p and q stand for. [13] In this sense, formal logic can be defined as the science of valid inferences. An alternative definition sees logic as the study of logical ...
A discourse marker is a word or a phrase that plays a role in managing the flow and structure of discourse.Since their main function is at the level of discourse (sequences of utterances) rather than at the level of utterances or sentences, discourse markers are relatively syntax-independent and usually do not change the truth conditional meaning of the sentence. [1]