What is the meaning of the following words: Qiyas (analogical reasoning), Istihsan (juristic preference), and Taqnin (codification)?

Qiyas (analogical deduction) is the assimilation of a subsidiary case (far‘) to a root case (asl) in ruling, due to the unity of the operative cause (‘illah) between them. Its pillars are four: the root case, the subsidiary case, the ruling (hukm), and the operative cause. An example of this is analogizing drugs to intoxicants in their prohibition, due to the operative cause of intoxication.

As for Istihsan (juristic preference), it comprises various types of inference. The best definition for it is the severance of specific issues from their analogues due to a particular evidence. An example of this is the sale of ‘araya, which was permitted by textual evidence despite being originally usurious (Istihsan by text).

Imam Al-Shafi’i criticized Istihsan based on mere intellect without evidence from the Qur’an or Sunnah, considering it legislation without Allah’s authority. This applies to codification and the enactment of laws by the state, which Al-Shafi’i referred to when he said: "Whoever employs Istihsan has legislated."