Istihsan is an Arabic term for juristic preference and is one of the methods of reasoning for understanding the sources of shariah and itjihad. The Arabic language (; , less formally, ) is the largest member of the Semitic branch of the Afro-Asiatic language family (classification: South Central Semitic) and is closely related to Hebrew and Aramaic. ... Sharia (Arabic شريعة also Sharia, Shariah or Syariah) is traditional Islamic law. ... Itjihad is the application of reason and reinterpretation to the message of the Koran. ...
Istihsan is used for fatwa in questions, not on the basis of its being a rule, but rather on the basis of its being an exception to the rule or according to the Maliki definition of consideration: relaxation of the rule is a temporary principle as distinct from a universal principle.
So istihsan in the Maliki school, as in the Hanafi school, is equivalent to analogy, even though the methods of the two schools in reaching it are different.
As for istihsan, it is only preventing the extremes of analogy: when implementing the analogy would result in injustice, or in something which is not recommended in itself, or to constriction and distress.
Istihsan as a concept is close to equity in Western law.
Istihsan is an important branch of law to the changing needs of society.
There is another form of Istihsan in which exception is made to the general rule for the sake of equity and justice on the basis of some 'nass' (textual evidence), approved custom, darurah (necessity) or Maslaha (public interest).