soundness, (1) (of an argument) the property of being valid and having all true premises; (2) (of a logic) the property of being not too strong in a certain respect. A logic L has weak soundness provided every theorem of L is valid. And L has strong soundness if for every set G of sentences, every sentence deducible from G using L is a logical consequence of G. See also COMPLETENESS, LOGICAL CONSEQUENCE , LOGICAL FORM , VALI. G.F.S.