Place مَا at the beginning to make a nominal statement negative. The original statement and its negative form describe the same subject, but the second denies the predicate.
Affirmative
Negative with مَا
Natural meaning
زَيْدٌ صَالِحٌ
مَا زَيْدٌ صَالِحًا
Zayd is pious → Zayd is not pious
الرَّجُلُ طَوِيلٌ
مَا الرَّجُلُ طَوِيلًا
The man is tall → The man is not tall
هَذَا بَشَرٌ
مَا هَذَا بَشَرًا
This is a human → This is not a human