Logic / Unit 4 Logic 128 short lesson, about 20 seconds
"If" vs. "Only If"
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The idea
"If" introduces the antecedent; "only if" introduces the consequent; "if and only if" welds them into ≡.
In practice
"You pass if you score 60" makes a 60 sufficient; "you pass only if you score 60" makes it merely required. Converse claims, not the same claim.
Where people slip
This pair sorts every logic student into two groups. Drill it until you're in the right one.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
Unlocks
- Nothing yet depends on this.
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