جريان الربا في الكثير يوجب جريانه في القليل
The application of the rule of riba to a large quantity is advanced as a reason for its application to a small one.
In the classical discussion of small and large quantities, a proposed analogy may assign one direction to the relationship between an attribute and the ruling. The opponent reverses that assumed dependence and asks whether the supposed cause is instead a consequence or correlate of another legal relationship.
The lesson is to distinguish the presence of a rule from the direction of causal explanation. Co-occurrence alone does not prove which factor is legally operative.