Logic / Unit 3 Logic 079 short lesson, about 20 seconds
Contradictories
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The idea
A and O are contradictories; so are E and I. Contradictories always have opposite truth values.
In practice
If "All S are P" is true, "Some S are not P" is false — necessarily, and vice versa.
Where people slip
This is the one square-of-opposition relation that survives every interpretation. The rest come with fine print.
Your place on the trail
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