Validity: From the Latin, validus, or strong, usually reduced to rigorous logical consistency of inferences from premises (philosophy) or replicatable demonstration of empirical claims (science), with neither required to be consistent with life requirements. By life-coherence principle, requires not only consistency of statements with each other and empirical evidence, but with the reproduction of life support systems.

From the Latin, validus, or strong, validity is narrowly equated in formalist traditions to inferences which are deducible from premises. Life coherent validity also requires consistency with known fact as well as life-enabling rather than disabling purpose. See Life Coherence Principle.

As a technical term used in logic, validity is that property of an argument that obtains when it is not possible for its premises to be true and the conclusion false. Validity can be a property of logical form. Thus the following form is valid: “Either p or q; not – p; therefore q.” Any argument that has this form is valid, e.g., “Swans are either black or white; they are not black; therefore they are white.” An argument is thus invalid if it is possible for the premises to be true and the conclusion false, e.g., “Swans are either black or white; they are white; therefore they are not black.” This form (Either p or qq; therefore not – p) is invalid.

Source: What is Good? What is Bad? The Value of All Values across Time, Place and Theories’ by John McMurtry, Philosophy and World Problems, Volume I-III, UNESCO in partnership with Encyclopedia of Life Support Systems: Oxford, 2004-11.