Secondary sources of the Islamic law
Four Islamic schools of law defined eight different secondary sources of Islamic law. 
1.	Qiyas is analogical reasoning. Qiyas is method by which additional case, which is not covered by direct text of the primary sources, can be ruled via primary sources using analogy. It has four constituents: a new case in need for legal ruling, an original case based on Quran or sunnah, an effective and common cause in both cases (new one and original one), and finally legal ruling on the new case.  (1)
2.	Maslahah is public interest. (2) Literally it means welfare, public interest. It is based on general objectives of Islamic law and the Hadith: “no harm nor harming”. (3)  there are two types of maslahah; public interest and what reason accepts but, against which exists no legal indication. Shafi’i school of law is the only school who does not accept maslahah as source of Islamic law. 
3.	Istihsan is juristic preference. It allows scholars (qadi-jurist) to abandon strong precedent for a weaker precedent in the interest of justice. The Hanafi school of law is known for its prominent use of istihsan. From the other side shafi’i school of law rejected legality of istihsan. 4
4.	Al- ‘Urf (Arabic: custom, knowledge). Custom can become source of Islamic law if it is compatible with the Quran and the sunnah. To become part of Urf and applicable as source for legal ruling, practice (custom) of given society must be general and common practice of the whole region, not small parts of the region and not occasionally. The Hanafi school of law with its early scholar Abu Yusuf (died 798) recognized Urf as independent source of Islamic law. 5
5.	Sadd al- Dhara’I is blocking the means. It is defined as blocking the means which would likely lead to an expected evil end if not obstructed. Sadd al-Dhara’i applies in situations when an allowed means is expected to lead to an unallowed result or when a legal means which normally lead to a legal result is being used to procure an unallowed end. 
References 

1.	The Oxford Encyclopaedia of the Islamic World. Jocelyn Hendrickson. 
2.	 The Oxford Encyclopaedia of the Islamic
3.	Ibn Majah. 
4.	 Encyclopaedia of Islam. Second Edition
5.	Encyclopaedia of Islam. Second Edition. Libson G. and Stewart F. H.