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  2. Vacuous truth - Wikipedia

    en.wikipedia.org/wiki/Vacuous_truth

    These examples, one from mathematics and one from natural language, illustrate the concept of vacuous truths: "For any integer x, if x > 5 then x > 3." [11] – This statement is true non-vacuously (since some integers are indeed greater than 5), but some of its implications are only vacuously true: for example, when x is the integer 2, the statement implies the vacuous truth that "if 2 > 5 ...

  3. If and only if - Wikipedia

    en.wikipedia.org/wiki/If_and_only_if

    The biconditional is true in two cases, where either both statements are true or both are false. The connective is biconditional (a statement of material equivalence), [2] and can be likened to the standard material conditional ("only if", equal to "if ... then") combined with its reverse ("if"); hence the name. The result is that the truth of ...

  4. Necessity and sufficiency - Wikipedia

    en.wikipedia.org/wiki/Necessity_and_sufficiency

    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 falsity of Q ensures the falsity of P .) [ 1 ] Similarly, P is sufficient for Q , because P being true always implies that Q is true, but P not being ...

  5. Contraposition - Wikipedia

    en.wikipedia.org/wiki/Contraposition

    If a statement's inverse is true, then its converse is true (and vice versa). If a statement's inverse is false, then its converse is false (and vice versa). If a statement's negation is false, then the statement is true (and vice versa). If a statement (or its contrapositive) and the inverse (or the converse) are both true or both false, then ...

  6. Truth condition - Wikipedia

    en.wikipedia.org/wiki/Truth_condition

    In semantics and pragmatics, a truth condition is the condition under which a sentence is true. For example, "It is snowing in Nebraska" is true precisely when it is snowing in Nebraska. Truth conditions of a sentence do not necessarily reflect current reality. They are merely the conditions under which the statement would be true. [1]

  7. Conditional sentence - Wikipedia

    en.wikipedia.org/wiki/Conditional_sentence

    The use of tenses is quite similar to English: In implicative conditional sentences, the present tense (or other appropriate tense, mood, etc.) is used in both clauses. In predictive conditional sentences, the future tense or imperative generally appears in the main clause, but the condition clause is formed with the present tense (as in English).

  8. Modus tollens - Wikipedia

    en.wikipedia.org/wiki/Modus_tollens

    The first premise is a conditional ("if-then") claim, such as P implies Q. The second premise is an assertion that Q, the consequent of the conditional claim, is not the case. From these two premises it can be logically concluded that P, the antecedent of the conditional claim, is also not the case. For example:

  9. IIf - Wikipedia

    en.wikipedia.org/wiki/IIf

    The above example would also eliminate the problem of IIf evaluating both its truepart and falsepart parameters. Visual Basic 2008 (VB 9.0) introduced a true conditional operator, called simply "If", which also eliminates this problem. Its syntax is similar to the IIf function's syntax: