Philosophy
Relevance Logic and the Paradoxes of Material Implication
Quick fact
Classical logic treats 'If P, then Q' as true whenever P is false — so 'If the moon is made of cheese, then unicorns exist' is automatically true, even though there's no connection between cheese moons and unicorns.
Why this is interesting
You've probably heard that 'If pigs fly, then I'm a millionaire.' Why does this feel like a joke, even though classical logic says it's true?