The Quran as evidence

الكتاب

The first dalil is the Quran. Every letter that reached us in the mutawatir Uthmani mushaf is Quran. A reading that is sahih, matches the rasm, and has an Arabic face is a recitation the fuqaha use. A shadh reading may explain a meaning; it is not a new ayah you can pray with.

Usul then asks how the wording works. Is this text decisive in meaning (qati) or open to more than one reading (zanni)? “Allah has made trade lawful and has forbidden riba” is qati in making a contrast. How far “riba” stretches is where the schools work.

قطعي الثبوت
Qati al-thubut
The text is established with certainty. The mushaf in your hand is this.
ظني الثبوت
Zanni al-thubut
Established with probability. A lone hadith is usually this. The Quran is not.
قطعي الدلالة
Qati al-dalalah
The meaning has one face. “Fast a numbered days” numbers the days of Ramadan.
ظني الدلالة
Zanni al-dalalah
The wording can carry more than one meaning. Most of fiqh lives here.

Worked example

Why Hanafis split fard and wajib

A ruling from a qati Quranic text is fard in the Hanafi school. A ruling from a lone sahih hadith is wajib. Both are required. The names mark the strength of the road, not two religions.

Tafsir is not usul. Tafsir asks what the ayah says. Usul asks what the ayah does as a command, a general word, or a limit.