Logic / Unit 6 Logic 269 short lesson, about 20 seconds
Existential Instantiation
Captions available
The idea
From (∃x)Fx, derive Fa — where a is a name new to the proof.
In practice
Something did it; call it a. But a must be a fresh name, carrying no prior commitments.
Where people slip
The strictest restriction in the system. Reusing an existing name quietly asserts that two somethings are the same something.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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