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  2. Tautology (logic) - Wikipedia

    en.wikipedia.org/wiki/Tautology_(logic)

    In mathematical logic, a tautology (from Ancient Greek: ταυτολογία) is a formula that is true regardless of the interpretation of its component terms, with only the logical constants having a fixed meaning. For example, a formula that states, "the ball is green or the ball is not green," is always true, regardless of what a ball is ...

  3. Logical truth - Wikipedia

    en.wikipedia.org/wiki/Logical_truth

    Logical truth is one of the most fundamental concepts in logic. Broadly speaking, a logical truth is a statement which is true regardless of the truth or falsity of its constituent propositions. In other words, a logical truth is a statement which is not only true, but one which is true under all interpretations of its logical components (other ...

  4. Contingency (philosophy) - Wikipedia

    en.wikipedia.org/wiki/Contingency_(philosophy)

    Contingency (philosophy) In logic, contingency is the feature of a statement making it neither necessary nor impossible. [ 1 ][ 2 ] Contingency is a fundamental concept of modal logic. Modal logic concerns the manner, or mode, in which statements are true. Contingency is one of three basic modes alongside necessity and possibility.

  5. Analytic–synthetic distinction - Wikipedia

    en.wikipedia.org/wiki/Analytic–synthetic...

    The analytic–synthetic distinction is a semantic distinction used primarily in philosophy to distinguish between propositions (in particular, statements that are affirmative subject – predicate judgments) that are of two types: analytic propositions and synthetic propositions. Analytic propositions are true or not true solely by virtue of ...

  6. Contradiction - Wikipedia

    en.wikipedia.org/wiki/Contradiction

    It is a proposition that is unconditionally false (i.e., a self-contradictory proposition). [2][3]This can be generalized to a collection of propositions, which is then said to "contain" a contradiction. History. [edit] By creation of a paradox, Plato's Euthydemusdialogue demonstrates the need for the notion of contradiction.

  7. Tautology (rule of inference) - Wikipedia

    en.wikipedia.org/wiki/Tautology_(rule_of_inference)

    In propositional logic, tautology is either of two commonly used rules of replacement. [1][2][3] The rules are used to eliminate redundancy in disjunctions and conjunctions when they occur in logical proofs. They are: The principle of idempotency of disjunction: and the principle of idempotency of conjunction: Where " " is a metalogical symbol ...

  8. Classical logic - Wikipedia

    en.wikipedia.org/wiki/Classical_logic

    Classical logic is a 19th and 20th-century innovation. The name does not refer to classical antiquity, which used the term logic of Aristotle. Classical logic was the reconciliation of Aristotle's logic, which dominated most of the last 2000 years, with the propositional Stoic logic. The two were sometimes seen as irreconcilable.

  9. Sequent calculus - Wikipedia

    en.wikipedia.org/wiki/Sequent_calculus

    hide. In mathematical logic, sequent calculus is a style of formal logical argumentation in which every line of a proof is a conditional tautology (called a sequent by Gerhard Gentzen) instead of an unconditional tautology. Each conditional tautology is inferred from other conditional tautologies on earlier lines in a formal argument according ...