Logic / Unit 3 Logic 100 short lesson, about 20 seconds
Rules Method: Quality Rules
Captions available
The idea
Rule 3: no syllogism with two negative premises is valid. Rule 4: a negative premise requires a negative conclusion, and vice versa.
In practice
Two exclusions can't build a connection — that's Rule 3 in one line.
Where people slip
Rule 4 cuts both directions. An affirmative conclusion from a negative premise fails just as hard as the reverse.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
Unlocks
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