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Validity and soundness are two criteria that we apply to subsets of deductive arguments.
A valid argument is one that has a form that would make it impossible for the conclusion to be false if the premises were true. Validity has nothing to do with whether or not the premises are actually true - the term describes the form an argument takes, rather than its content.
An invalid argument is one with a flawed form. For example, there is a problem with any argument that goes: If A then B, not A therefore not B. Why? Think about it: If a canon is fired then there's a loud noise. Now suppose the canon isn't fired. That doesn't mean it's guaranteed there won't be a loud noise, because loud noises can be caused by many other things besides a cannon firing!
A sound argument is one that is both valid and has true premises.
Let's try a practice exercise...
Sort the white boxes into categories according to whether the arguments they contain are invalid, valid but unsound, or sound.
Drag this image onto the workspace to proceed. You must be using the inbuilt browser in Rationale 1.3 or later.
After you've finished this exercise drag this thumbnail onto the workspace to see the model answer:
This material has been developed independently of the International Baccalaureate, which in no way endorses it.
© Austhink 2013. Rationale Exercises version 0.1, Jan-13
