«ما يكون الحكم في الفرع من جنس الحكم الثابت في الأصل»
An analogy in which the new ruling belongs to the broader legal genus of the original ruling.
The textbook relates easing some permission requirements on account of frequent movement to the prophetic ruling concerning a cat’s leftover water. The precise legal questions differ, yet both are discussed with reference to relieving hardship where frequent movement occurs.
In the first type, the specific kind of ruling is shared. In the second, rulings can differ in their particulars while sharing a broader legal category and relevant rationale.