An illah is the legally effective attribute to which a ruling is attached. A sabab may be an observable trigger sometimes substituted for a less evident cause. A shart is necessary for validity or operation but is not always sufficient. A mani prevents a ruling from arising or continuing.
Ablution is a condition for valid prayer, but performing ablution is not itself performing the prayer. Even where a cause is present, an impediment may change the outcome. Objections such as denial, distinction, counterexample and conflicting argument test the soundness of an analogy.