Uṣūl al-Fiqh, or the Principles of Islamic Jurisprudence, serves as the foundational framework from which all derived rulings (furū‘) originate. Linguistically, uṣūl refers to the “roots” or “bases” of something, while technically, it refers to the body of knowledge that outlines the rules and methods to extract legal rulings from primary sources—al-Kitāb (Qur’an) and as-Sunnah (Prophetic tradition).

It is important to note that Uṣūl al-Fiqh is not a purely theoretical science; it is applied knowledge. Scholars study it to derive rulings, not merely to theorize. As al-Zarkashī (raḥimahullāh) stated:

فَإِنَّهُ قَاعِدَةُ الشَّرْعِ وَأَصْلٌ يَرِدُّ إِلَيْهِ كُلُّ فَرْعٍ
“It is the foundation of Sharī‘ah, to which every branch returns.”

Similarly, Ibn Khaldūn (raḥimahullāh) emphasized that earlier generations of the Salaf did not require formal Uṣūl sciences, as their understanding of language and Qur’anic terms sufficed for deriving rulings.