Soundness
From Wikinfo
An argument is sound if, and only if, (1) the argument is valid
and (2) all of its premises are true.
So suppose we have a sound argument:
- All men are mortal.
- Socrates is a man.
- Therefore, Socrates is mortal.
In this case we have an argument where, first, if the premises are all true, then the conclusion must be true (i.e., the argument is valid); and, second, it so happens that the premises are all true. It follows that the conclusion must be true. That is the nice thing about soundness: if you know an argument is sound, then you know that its conclusion is true. By definition, all sound arguments have true conclusions. So soundness is a very good quality for an argument to have.
In mathematical logic, a formal deduction calculus is said to be sound with respect to a given logic (i.e. wrt its semantics) if every statement that can be derived within this calculus is a tautology of the logic. Stated differently, this says that everything that can be formally (syntactically) calculated is semantically true. The reverse condition is called completeness.
References
- Adapted from the Wikipedia article, "Soundness" http://en.wikipedia.org/wiki/Soundness, used under the GNU Free Documentation License
