Logic / Unit 1 Logic 012 short lesson, about 20 seconds
Invalidity
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The idea
An argument is invalid when the premises could all be true while the conclusion is false.
In practice
"All dogs are mammals; Rex is a mammal; so Rex is a dog." Rex could be a cat. Invalid.
Where people slip
One possible counterexample is enough. You don't need the premises to actually be false.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
Builds on
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