An impediment (mani') may obstruct the legal effect at a distinct stage, even where a cause or operative factor is present. The fourfold Hanafi scheme distinguishes impediments to the formation of the cause, completion of the cause, commencement of the ruling and continuation of the ruling.
Where a cause never forms, the legal basis is absent. Where its constituent requirements remain incomplete, completion is blocked. In other cases the cause exists but a ruling cannot begin, or an already operative ruling cannot continue.
For example, in contracts, conditional rulings, testimony and completion of the zakat year, “there is an impediment” is insufficient analysis until its precise stage is identified.
Some jurists who reject the relevant form of specification of a cause arrange these impediments into three classes; this reflects a substantive methodological difference.