والانفعال: هو خروج الشيء من القوة إلى الفعل على سبيل التدريج.
Passion is a thing's gradual passage from potentiality to actuality: undergoing an effect and changing state.
Water in a vessel becomes heated by the fire. The water is undergoing the effect, so this is an illustration of infi‘āl.
In ordinary language, acting and being affected can mean many things. Here action and passion are opposite aspects of the same progressive change.