الفتاح
كلمة (الفتّاح) في اللغة صيغة مبالغة على وزن (فعّال) من الفعل...
In analogy, it refers to the basic rule, as opposed to the subsidiary rule.
"Asl" (basic rule/original ruling) is one of the four basic elements of "qiyās" (analogy), which are : "asl", "far‘" (parallel case), "‘illah" (effective cause) and "hukm" (ruling). For example, if someone draws an analogy between corn and wheat - as both are measurable - in terms of the involvement of interest in the latter, then in this case wheat is the "asl", corn is the "far‘", being measurable is the "‘illah", and the prohibition of interest is the "hukm".
"Asl": it is derived from "asl", which means the foundation of something upon which its existence depends.
The evidence, whether it is a religious text or derived through reasoning.