ConstructionMain assertionRole of the state
زَيْدٌ رَاكِبٌZayd is ridingPrincipal predicate
جَاءَ زَيْدٌ رَاكِبًاZayd cameCircumstantial qualifier
In the first case riding is the very fact asserted. In the second it specifies the manner of an arrival. This is why a circumstantial modifier can be closely attached without introducing a coordinating wāw; it fills a role within the predication rather than creating a parallel report.
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Appendix to Faṣl and Waṣl: Circumstantial Clauses, Wāw and Pronominal Linkage
ConstructionMain assertionRole of the state
زَيْدٌ رَاكِبٌZayd is ridingPrincipal predicate
جَاءَ زَيْدٌ رَاكِبًاZayd cameCircumstantial qualifier
In the first case riding is the very fact asserted. In the second it specifies the manner of an arrival. This is why a circumstantial modifier can be closely attached without introducing a coordinating wāw; it fills a role within the predication rather than creating a parallel report.