Logic / Unit 1 Logic 011 short lesson, about 20 seconds
Validity
Captions available
The idea
An argument is valid when it is impossible for the premises to be true and the conclusion false. The form guarantees the transfer of truth.
In practice
"All dogs are mammals; Rex is a dog; so Rex is a mammal." No possible world breaks this.
Where people slip
Validity is all-or-nothing. There is no "mostly valid."
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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