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Articles

Teaching Validity with a Stanley Thermos

Andrew Chrucky on logical arguments which hold water. And coffee.

I teach critical thinking and logic, and I would like to share with Philosophy Now readers a useful way of understanding the concept of deductive validity by an analogy to a thermos flask. I know that some people find it difficult to distinguish the truth of a logical argument’s premises from the validity of an argument. They think that a valid argument has all true statements, and an invalid one a false premise. Nothing could be further from the case, but to understand the difference between truth and validity we need to introduce the idea of an argument form, for it is the form which is the vehicle of validity, not what is put in the form. An argument form does not contain statements (but statement forms), so there is nothing in the form to be true or false.

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