«والسالبة الكلية تنعكس إلى سالبة جزئية»
A universal negative yields a particular negative in this traditional scheme.
Original: No human is a horse.
Result: Some nonhorses are not nonhumans.
“Nonhorse” is the new subject, “nonhuman” the new predicate, and the copula remains negative. The particular conclusion also reflects the traditional assumption that humans exist.
The printed example has «بعض اللافرس ليس بالإنسان»
“Some nonhorses are not human.”
That assertion might be true in some circumstances, but it does not follow from the premise alone. By the stated earlier definition, the complement “nonhuman” is needed in the predicate.