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 of logic is said to be valid if it is true under every interpretation (also called structure or model). See also model theory or mathematical logic#technical reference.

• In logic, a tautology or tautologous formula is a valid formula of sentential logic. See also 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.)

The two notions of logical validity are closely related. (1) Every valid formula is the conclusion of a valid argument with no premises. (2) For every valid argument, there is a corresponding valid formula. for example, corresponding to the valid syllogism above is the valid (rather informal) formula:

If (all P are Q) and (A is P), then (A is Q).

• In the social sciences: validity (psychometric)
• In Catholic theology

See also:

• soundness