Reasoning by analogy means assigning to a branch the same legal value as the root, by means of a characteristic that they have in common.
There are three kinds of analogy: analogy by common characteristic, by indication, and by resemblance. Analogy by common characteristic is analogy in which the common characteristic entails the legal value. Analogy by indication is using one case as evidence for a parallel case; it is when the common characteristic indicates the legal value but does not entail it. Analogy by resemblance is when a branch could be related to either of two roots, so it is related to the one that most resembles it.
The branch must correspond to the root. The root must be established by evidence that is accepted by both parties.1 The common characteristic must be consistent in what it entails, without exception either in expression or in meaning. The legal value must be coextensive with the common characteristic, absent where it is absent and present where it is present. The common characteristic brings about the legal value, and the legal value is brought about by the common characteristic.
- (reasoning by) analogy: qiyās
- branch: farʿ
- root: aṣl
- common characteristic: ʿilla
- indication: dalāla
- resemblance: shabah