Suppose Zayd was once uneducated and later became learned. His knowledge changed, but his being human did not change.
Initially: 'Zayd is not learned.'
Later: 'Zayd is learned.'
Throughout: 'Zayd is human.'
This shows why possessing or losing a quality is different from that quality belonging to the definition of one's kind.
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A person changes but remains human
Essence, Quiddity, and Essential vs Accidental Universals
Suppose Zayd was once uneducated and later became learned. His knowledge changed, but his being human did not change.
Initially: 'Zayd is not learned.'
Later: 'Zayd is learned.'
Throughout: 'Zayd is human.'
This shows why possessing or losing a quality is different from that quality belonging to the definition of one's kind.