Philosophy
The Logic of Relevance Logic and the Relevance Condition
Quick fact
Classical logic accepts the argument 'If pigs can fly, then I am the king of France' as valid, but relevance logic rejects it because the premise and conclusion share no content—a violation of the relevance condition.
Why this is interesting
You know that if you drop a glass, it breaks—but did you know that in classical logic, from 'the moon is made of cheese' you can derive '2+2=5'? How can that be?