«يوجد الحكم بوجوده، وينعدم بانعدامه»
A ruling is present with the cause and absent when it is absent.
This is the book’s formulation of the link between an operative cause and its ruling. It should not be read as ignoring all other relevant conditions or impediments. If a legally significant impediment exists, further analysis may be needed before applying a ruling.
In qiyas, we first establish the cause in the original case, then verify that the same cause actually exists in the new one. Comparable rulings depend on a comparable legal cause, not on resemblance in irrelevant details.