Soundness: As a technical term in logic, soundness refers to that property which obtains when the premises of an argument are true and the argument is valid. Some consider soundness to be necessary and sufficient for an argument to be a good one. That is ,an argument that lacks either property is not a good argument; and an argument that exhibits both is a good one. However, soundness is too narrow a criterion of good argument, since some invalid arguments (such as strong inductive ones) are logically good and some arguments whose premises cannot be known to be true (although it is more reasonable to believe them than not to) are still logically good arguments. Soundness is also too broad a criterion, for any argument that begs the question and has true premises will be sound. Thus, the following argument would be sound: Canada is a parliamentary democracy, so parliamentary democracy is the form of government in Canada. But it is not a logically good argument.

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.