In the name of Allah. All praise is due to Allah, and may blessings and peace be upon the Messenger of Allah. To proceed:

These maxims and their commentary have been distilled from several works devoted to legal maxims. In every source we consulted, however, we exercised some abridgement, adjustment, and clarification so that the material would be suitable for anyone seeking quick benefit and easily gathered fruit.

Definition and historical background:
Linguistically, a qāʿidah is the foundation of a thing, like the base of a building and the like.
Technically, it is a predominant ruling that applies to most of its particular instances.
Thus, it is a comprehensive juristic principle couched in concise wording that contains general legislative rulings, and—despite its breadth—its formulation is marked by brevity.
These are predominant, not universally constant, rulings; they convey the basic juristic idea that expresses the overarching analogical method, yet analogy often falters in certain issues that call for discretionary solutions. Consequently, they are not without exceptions in the applied branches of the law, for jurists consider those exceptional cases more suitably assigned to another maxim.
Still, the fact that the maxims are only predominant does not detract from their scholarly worth, for they provide a superb portrayal of general juristic conclusions and a disciplined framework for the practical legal branches, showing within each group of those branches the shared rationale and point of connection.
Al-Qarāfī said: “The legal maxims are of tremendous benefit. In proportion to one’s mastery of them, the stature of the jurist grows and the paths of issuing fatwas become clear to him. Whoever gathers isolated branches without the universal maxims will find those branches contradictory and confused.
But whoever disciplines his study of jurisprudence through its maxims can dispense with recording most of the individual cases;”