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Modal logic is a type of formal logic primarily developed in the 1960s that extends classical propositional and predicate logic to include operators expressing modality . Modals—words that express modalities—qualify a statement. For example, the statement "John is happy" might be qualified by saying that John is usually happy, in which case the term "usually" is functioning as a modal.
Ignoratio elenchi , also known as irrelevant conclusion , [ 1 ] is the informal fallacy of presenting an argument that may or may not be logically valid , but fails nonetheless to address the issue in question. Ignoratio elenchi falls into the broad class of relevance fallacies. [ 2 ] It is one of the fallacies identified by Aristotle in his Organon . In a broader sense he asserted that all fallacies are a form of ignoratio elenchi . [ 3 ] [ 4 ] Ignoratio Elenchi , according to Aristotle, is a fallacy which arises from “ignorance of the nature of refutation.”
The principle of explosion , ( Latin : ex falso quodlibet or ex contradictione sequitur quodlibet , "from a contradiction, anything follows") or the principle of Pseudo-Scotus , [ citation needed ] is the law of classical logic , intuitionistic logic and similar logical systems, according to which any statement can be proven from a contradiction. [ 1 ] That is, once a contradiction has been asserted, any proposition (or its negation) can be inferred from it. In symbolic terms, the principle of explosion can be expressed in the following way (where " " symbolizes the relation of logical consequence ): or
Gödel's incompleteness theorems are two theorems of mathematical logic that establish inherent limitations of all but the most trivial axiomatic systems capable of doing arithmetic . The theorems, proven by Kurt Gödel in 1931, are important both in mathematical logic and in the philosophy of mathematics . The two results are widely, but not universally, interpreted as showing that Hilbert's program to find a complete and consistent set of axioms for all mathematics is impossible, giving a negative answer to Hilbert's second problem . The first incompleteness theorem states that no consistent system of axioms whose theorems can be listed by an " effective procedure " (e.g., a computer program, but it could be any sort of algorithm) is capable of proving all truths about the relations of the natural numbers ( arithmetic ).
Fuzzy logic is a form of many-valued logic or probabilistic logic ; it deals with reasoning that is approximate rather than fixed and exact. Compared to traditional binary sets (where variables may take on true or false values ) fuzzy logic variables may have a truth value that ranges in degree between 0 and 1. Fuzzy logic has been extended to handle the concept of partial truth, where the truth value may range between completely true and completely false. [ 1 ] Furthermore, when linguistic variables are used, these degrees may be managed by specific functions. The term "fuzzy logic" was introduced with the 1965 proposal of fuzzy set theory by Lotfi A. Zadeh . [ 2 ] [ 3 ] Fuzzy logic has been applied to many fields, from control theory to artificial intelligence .
In logic , a three-valued logic (also trivalent , ternary , or trinary logic , sometimes abbreviated 3VL ) is any of several many-valued logic systems in which there are three truth values indicating true , false and some indeterminate third value. This is contrasted with the more commonly known bivalent logics (such as classical sentential or boolean logic ) which provide only for true and false . Conceptual form and basic ideas were initially created by Łukasiewicz , Lewis and Sulski . These were then re-formulated by Grigore Moisil in an axiomatic algebraic form, and also extended to n -valued logics in 1945. [ edit ] Representation of values