124. ANALOGY, SYSTEMATIC REASONING,

qiyās is that a qiyās cannot be based on a special case which constitutes an exception from a general rule; in other words, that exceptions cannot be extended by analogy.¹ This rule is valid within the sphere of the sunna of the Prophet, and between Koran and sunna (Ris. 75). It is also valid as regards consensus: a decision of an exceptional and unsystematic character, sanctioned by consensus, must not be extended by analogy beyond its original field; but within this, qiyās may be used (ibid. 81). The necessary corollary is that an exemption from a general rule must be based on incontrovertible proof (Ikh. 256). Shāfi'ī formulates the principle underlying his rule as: 'Legal institutions must not be treated by analogy with one another' (lā tuqās sharī'a 'alā sharī'a) (Tr. III, 34).

Qiyās is used on questions of detail, which are the concern of specialists only (Ris. 50). It is the opposite of istiḥsān because it is based on indications (dalā'il) and parallels (mithāl), and it is comparable to the opinions of experts on questions of fact (Tr. VII, 272 f.). But being subject to differences of opinion it does not convey certainty (iḥāṭa) (Tr. IV, 255). Shāfi'ī recognizes its limits, in opposition to the ahl al-kalām (Tr. I, 122), and no further qiyās can be based on the result of a qiyās (ibid. 51).

A particular kind of qiyās is represented by conclusions a potiori ²and by conclusions a maiore ad minus or, conversely, a minore ad maius. Shāfi'ī gives the theory in Ris. 70 f.: 'The strongest kind of qiyās is the deduction, from the prohibition of a small quantity, of the equally strong or stronger prohibition of a great quantity; from the commendation of a small act of piety, of the presumably stronger commendation of a greater act of piety; from the permission of a great quantity, of the presumably even more unqualified permission of a smaller quantity. ... Some scholars do not call this qiyās, but consider it to fall under the original ruling, and likewise when something is equivalent to (fī ma'nā ...) something allowed or forbidden, so that it is also allowed or forbidden; they reserve the term qiyās for cases where there is a possible parallel which can be construed in two ways, one of which is chosen to the exclusion