The four schools of Sunni Law derive their guidance from the Quran and the Sunnah as the primary sources, and ijmā' (consensus of opinion) and qiyās (analogical deduction) as the secondary sources. Qiyās, which plays an important role in the Hanafi school, the largest of the four Sunni schools, is used to provide answers to new problems by drawing analogy between the accepted interpretations of the two primary sources in relation to the problems already solved by them and the reasons underlying the new problem at hand.
These sources represent God's Will for regulating the conduct of the community of Islam and are also known as the Sharī'ah. The Sharī'ah signifies a composite source of teachings and practices based upon the interrelation between divine and human activity. It is considered a duty of every Sunni Muslim to spend his life according to the dictates of the Sharī'ah as interpreted by the 'ulama' (learned men) and the fuqaha' (jurists).
All Sunni schools provide for their adherents clear guidelines drawn from the light of the Quran and the Sunnah for all walks of life and every sphere of activity. For example, rules have been laid down for performing prayers, for formulating contracts of sale and purchase, for conduct of war, for dealing with non-Muslims, for marriage, divorce, inheritance, etc.
Certain minor differences of opinion and interpretation exist among the four Sunni schools, but a Sunni Muslim may conform his practice of Islam to any one of them. Usually a person born in one school conforms to the practice of that same school. This is called taqlīd, or imitation. But there are at present a number of Sunni Muslims who belong to the Salafiyyah movement, which claims that it is sufficient to follow the Quran and the Sunnah and that there is no need to follow any of the four Imams. The puritanical movement of Shaykh Muḥammad ibn 'Abd al-Wahhāb, popularly known as the Wahhabī movement, rejects the taqlīd of any of the four Imams and their schools of thought. Another group, named Ahl al-hadith, which is found in India and Pakistan, also follows the Quran and Hadith and not the four Sunni schools of Islamic jurisprudence. It feels that the Quran and the Sunnah are sufficient to guide it upon the right path.