A subject can change over time.
Example 1: Zayd was present yesterday.
Example 2: Zayd is not present today.
These do not contradict. Contrast 'Zayd was present at 9 a.m. today' with 'Zayd was not present at 9 a.m. today,' with all other circumstances fixed.
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Identity of time
Contradiction and the Eight Conditions
A subject can change over time.
Example 1: Zayd was present yesterday.
Example 2: Zayd is not present today.
These do not contradict. Contrast 'Zayd was present at 9 a.m. today' with 'Zayd was not present at 9 a.m. today,' with all other circumstances fixed.