Validity

VanDusen Botanical Gardens

BLACKBURN, SIMON (1996) Oxford Dictionary of Philosophy, Oxford, Oxford University Press.

Interesting from philosopher Blackburn:

The primary meaning of validity, (philosophically, my add), is that within arguments, a conclusion (s) follows from premises. (389).

Premises and conclusions are not valid in themselves, but are true or false. (389).

Validity requires the correct form of logic. A valid argument. This can also be seen in my book reviews of the following...

LANGER, SUSANNE K (1953)(1967) An Introduction to Symbolic Logic, Dover Publications, New York.

PIRIE, MADSEN (2006)(2015) How To Win Every Argument, Bloomsbury, London.

Stanford University

Valid: an argument is valid if and only if it is necessary that if all of the premises are true, then the conclusion is true; if all the premises are true, then the conclusion must be true; it is impossible that all the premises are true and the conclusion is false. 

(Cannot have true premises and false conclusion (TF) for validity, my add)

Invalid: an argument that is not valid. We can test for invalidity by assuming that all the premises are true and seeing whether it is still possible for the conclusion to be false. If this is possible, the argument is invalid. 

Validity and invalidity apply only to arguments, not statements. For our purposes, it is just nonsense to call a statement valid or invalid. 

True and false apply only to statements, not arguments. For our purposes, it is just nonsense to call an argument true or false. All deductive arguments aspire to validity.  

Sound: an argument is sound if and only if it is valid and contains only true premises. Unsound: an argument that is not sound.

Valid: Argument (s)

True: Premises and conclusion (s)

Notice, I will at times state that something is reasonable. This connects to the idea of validity, not necessarily truth or soundness. Although it may be so, in my view.