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  2. Contraposition - Wikipedia

    en.wikipedia.org/wiki/Contraposition

    Contraposition. In logic and mathematics, contraposition, or transposition, refers to the inference of going from a conditional statement into its logically equivalent contrapositive, and an associated proof method known as § Proof by contrapositive. The contrapositive of a statement has its antecedent and consequent inverted and flipped.

  3. Contradiction - Wikipedia

    en.wikipedia.org/wiki/Contradiction

    In traditional logic, a contradiction occurs when a proposition conflicts either with itself or established fact. It is often used as a tool to detect disingenuous beliefs and bias . Illustrating a general tendency in applied logic, Aristotle 's law of noncontradiction states that "It is impossible that the same thing can at the same time both ...

  4. Material conditional - Wikipedia

    en.wikipedia.org/wiki/Material_conditional

    Mathematical logic. Philosophy of logic. Category. v. t. e. The material conditional (also known as material implication) is an operation commonly used in logic. When the conditional symbol is interpreted as material implication, a formula is true unless is true and is false.

  5. Proof by contradiction - Wikipedia

    en.wikipedia.org/wiki/Proof_by_contradiction

    In logic, proof by contradiction is a form of proof that establishes the truth or the validity of a proposition, by showing that assuming the proposition to be false leads to a contradiction. Although it is quite freely used in mathematical proofs, not every school of mathematical thought accepts this kind of nonconstructive proof as ...

  6. Hypothetical syllogism - Wikipedia

    en.wikipedia.org/wiki/Hypothetical_syllogism

    A mixed hypothetical syllogism has two premises: one conditional statement and one statement that either affirms or denies the antecedent or consequent of that conditional statement. For example, If P, then Q. P. ∴ Q. In this example, the first premise is a conditional statement in which "P" is the antecedent and "Q" is the consequent.

  7. Paradoxes of material implication - Wikipedia

    en.wikipedia.org/wiki/Paradoxes_of_material...

    A material conditional formula is true unless is true and is false. If natural language conditionals were understood in the same way, that would mean that the sentence "If the Nazis had won World War Two, everybody would be happy" is vacuously true.

  8. If and only if - Wikipedia

    en.wikipedia.org/wiki/If_and_only_if

    In logic and related fields such as mathematics and philosophy, " if and only if " (often shortened as " iff ") is paraphrased by the biconditional, a logical connective [1] between statements. The biconditional is true in two cases, where either both statements are true or both are false. The connective is biconditional (a statement of ...

  9. Necessity and sufficiency - Wikipedia

    en.wikipedia.org/wiki/Necessity_and_sufficiency

    In logic and mathematics, necessity and sufficiency are terms used to describe a conditional or implicational relationship between two statements. For example, in the conditional statement: "If P then Q ", Q is necessary for P, because the truth of Q is guaranteed by the truth of P. (Equivalently, it is impossible to have P without Q, or the ...