كَأَنَّ زَيْدًا أَسَدٌ
It is as though Zayd were a lion.
«كَأَنَّ» belongs to the particles resembling verbs: it puts its subject in the accusative and its predicate in the nominative. Here زَيْدًا is its accusative subject and أَسَدٌ is its nominative predicate. The construction invites a comparison of Zayd with a lion.
The two constructions with kāf and kaʾanna should not be assigned an identical rhetorical force in all contexts. Kaʾanna may also convey an impression concerning the probability of an assertion. Its grammatical government and rhetorical function require separate analysis.