interpretation of the symbolism of that language. Thus, not all sound deductive systems are complete in this special sense of completeness, in which the class of models (up to isomorphism) is restricted to the intended one. The original completeness proof applies to all classical models, not some special proper subclass of intended ones. See also Soundness (interactive proof) References Bibliography Boolos, Burgess, Jeffrey. Computability and Logic, 4th Ed, Cambridge, 2002. External links Validity and Soundness in the Internet Encyclopedia of Philosophy. Arguments Concepts in logic Deductive reasoning Model theory Proof theory