The mere presence of a verb does not establish causal linkage. We must ask whether the act or quality belongs directly to the primary subject or to another person or thing connected with that subject.
ExpressionWho bears the predication?Relation
زَيْدٌ قَائِمٌZaydDirect, non-causal
زَيْدٌ قَامَ أَبُوهُZayd's fatherCausal via the father
زَيْدٌ أَبُوهُ مُنْطَلِقٌZayd's fatherCausal nominal-clause relation
Although Zayd is the initial subject in all three, the internal target of predication changes. Recognizing that is essential to the rule about singular predicates.