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# Science Fair Project Encyclopedia

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# Validity

In logic, an argument is said to be valid if the truth of the conclusion follows from the truth of the premises.

A formula is said to be valid (or tautologous) if it is true under every valuation (also interpretation). Refer to the truth table article.

Consider the following argument form in which the letters P, Q, and A represent unanalyzed or uninterpreted sentences.

All P are Q
A is P
Therefore, A is Q

We can determine the validity of an actual argument by translating it into an argument form, and then analyzing the argument form for validity. (The argument form above is valid; see syllogism.)