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  2. Validity (logic) - Wikipedia

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

    The corresponding conditional of a valid argument is a logical truth and the negation of its corresponding conditional is a contradiction. The conclusion is a necessary consequence of its premises. An argument that is not valid is said to be "invalid". An example of a valid (and sound) argument is given by the following well-known syllogism:

  3. Falsifiability - Wikipedia

    en.wikipedia.org/wiki/Falsifiability

    So observations have two purposes in Popper's view. On the methodological side, observations can be used to show that a law is false, which Popper calls falsification. On the logical side, observations, which are purely logical constructions, do not show a law to be false, but contradict a law to show its falsifiability.

  4. Mathematical proof - Wikipedia

    en.wikipedia.org/wiki/Mathematical_proof

    Eudoxus (408–355 BCE) and Theaetetus (417–369 BCE) formulated theorems but did not prove them. Aristotle (384–322 BCE) said definitions should describe the concept being defined in terms of other concepts already known. Mathematical proof was revolutionized by Euclid (300 BCE), who introduced the axiomatic method still in use today.

  5. Direct proof - Wikipedia

    en.wikipedia.org/wiki/Direct_proof

    Traditionally, a proof is a platform which convinces someone beyond reasonable doubt that a statement is mathematically true. Naturally, one would assume that the best way to prove the truth of something like this (B) would be to draw up a comparison with something old (A) that has already been proven as true. Thus was created the concept of ...

  6. Gödel's incompleteness theorems - Wikipedia

    en.wikipedia.org/wiki/Gödel's_incompleteness...

    It is not possible to replace "not provable" with "false" in a Gödel sentence because the predicate "Q is the Gödel number of a false formula" cannot be represented as a formula of arithmetic. This result, known as Tarski's undefinability theorem , was discovered independently both by Gödel, when he was working on the proof of the ...

  7. 105 True or False Questions—Fun Facts To Keep You ... - AOL

    www.aol.com/lifestyle/105-true-false-questions...

    Answer: False – Eric the Red was Leif Erikson’s dad. 98. Facebook was the first social media website. Answer: False – Six Degrees is considered the first social media site, launched in 1996. 99.

  8. Proof by contradiction - Wikipedia

    en.wikipedia.org/wiki/Proof_by_contradiction

    In this general sense, proof by contradiction is also known as indirect proof, proof by assuming the opposite, [2] and reductio ad impossibile. [3] A mathematical proof employing proof by contradiction usually proceeds as follows: The proposition to be proved is P. We assume P to be false, i.e., we assume ¬P. It is then shown that ¬P implies ...

  9. Logical reasoning - Wikipedia

    en.wikipedia.org/wiki/Logical_reasoning

    For valid arguments, it is not important whether the premises are actually true but only that, if they were true, the conclusion could not be false. Valid arguments follow a rule of inference, such as modus ponens or modus tollens. Deductive reasoning plays a central role in formal logic and mathematics.