QuestionMutualityMultiplicity
Main focusAction directed reciprocallyMore than one doer
Illustrationتَشَاتَمَ زَيْدٌ وَعَمْرٌوتَرَافَعَا شَيْئًا
MeaningThe two insult each otherThe two lift an object
Both involve several people, but mutuality highlights reciprocal engagement; multiplicity highlights plural agents issuing the action. A dual ending by itself does not establish mutual action.