Usul al-Fiqh

Definition
Usul al-fiqh is defined from two angles:

First: by examining its two constituent terms, namely usul and fiqh.
• Usul (sing. asl) denotes the foundations upon which something else is built. Thus the asl of a wall is its base, and the asl of a tree is the trunk from which its branches spread. Allah the Exalted says, “Do you not see how Allah sets forth a parable? A good word is like a good tree—its roots are firm and its branches reach the sky” (14:24).

• Linguistically, fiqh means understanding, as in the supplication of Moses: “Untie the knot from my tongue” (20:27). Technically, it is “the knowledge of the practical Shariʿah rulings along with their detailed proofs.”

By the word “knowledge” (maʿrifah) we include both certainty and probability, for one’s perception of jurisprudential rulings may at times be definitive and at other times conjectural, as is the case in many fiqh matters.

By the phrase “the Shariʿah rulings” we mean those rulings derived from revelation, such as obligation and prohibition. This wording excludes rational judgments—like knowing that the whole is greater than the part—and customary judgments—like knowing that dew will descend on a cold night when the sky is clear.