Compare syntactic participation and selected lexical meanings of derived forms.
FormExampleMeaning here
IIIقَاتَلَ زَيْدٌ عَمْرًاReciprocal engagement with an object partner
VIتَشَاتَمَ زَيْدٌ وَعَمْرٌوBoth participants are co-subjects
VIIIاِكْتَسَبَAcquiring through deliberate action
XاِسْتَطْعَمَSeeking food
تَمَارَضَ زَيْدٌ
Translation: Zayd pretended to be ill.
اِسْتَحْسَنْتُهُ
Translation: I considered it good.
The first illustrates feigning; the second judgment. Not every Form X verb expresses seeking, nor every Form III verb actual shared fighting.