An expression sometimes requires an unspoken meaning to become rationally or legally coherent. Such a term cannot be inserted at whim. Iqtida involves what must be understood for the statement's intended sense or legal validity to hold.
Consider the educational phrase “Ask this town.” In an ordinary context it means asking the town's people, with “people” understood rather than stated. This illustrates the interpretive method; the precise legal operation of iqtida still depends on the actual source and its conditions.