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We're employing a specialized technical philosophical use of the word 'valid' when we say that a valid argument is one that has good form, regardless of the truth of its premises.
In ordinary language 'valid' is often used differently - we say things like 'that's a valid point' when we mean 'yes, the content of what you've said is true'.
The word 'valid' is being applied to two different things: in the specialized philosophical usage we're applying the term to the quality of the logical connections in the argument (form), whereas in the everyday usage we're applying the term to individual premises or assumptions (content).
As Martin Davies & Kenneth Sievers point out, it doesn't really matter whether philosophers can convince people on the street to use the word 'valid' only in the technical sense. What is really important, they say, is for IB students to understand that reasoning can fail in two different ways:
(see The Nature of Knowing, IBID Press, Victoria, 2006, p. 277)
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
