A qiyas can be analyzed in four components:
1. Aṣl: the original case whose ruling is established.
2. Farʿ: the new case requiring a ruling.
3. Ruling of the original: the legal result established by evidence.
4. ʿIllah: the legally effective attribute through which that ruling extends.
Application: When comparing duties discharged on behalf of another person, one must identify the authoritative original rule and its relevant cause. Merely observing that both acts are duties is not sufficient in every context.
If the original ruling is unestablished, or the relevant cause does not occur in the new case, the proposed result is not a sound qiyas.