What is the reason and method for the adoption of the four schools of thought, to the exclusion of others, by the Ahl al-Sunnah wal-Jama’ah, and what is the wisdom behind their existence given the sufficiency of the Quran, the Sunnah, and the interpretations of the Companions? Who adopted them, and why did other schools of thought that emerged in their era and were identical to them not persist? And how did the four Imams differ on subsidiary matters despite stemming from a single source?