Is unattested inference (istidlal, a ruling on an interest with no specific base) a valid proof?

Imam al-Haramayn al-Juwayni devotes the "fourth book" of al-Burhan to inference (istidlal), defining it as a meaning that suggests and suits a ruling to rational reflection without an agreed base, to which reasoning by cause applies. ¹ He says the recognised scholars divided over it into three positions. ²

• Rejection: al-Qadi al-Baqillani and groups of the school's theologians rejected inference and limited meaning to what rests on a base. ¹
• Unrestricted acceptance: al-Juwayni attributes to Malik ibn Anas allowing the following of considerations of interest and soundness whether near to or far from the texts, so long as no base in the Book, sunna or consensus excludes them, and describes him as having "gone to excess" in this. ^{1 2}
• Acceptance on condition of closeness: he attributes to al-Shafi'i and most followers of Abu Hanifa relying on inference even without an agreed base, provided it is not remote or excessive and the interests resemble those agreed to be valid. ^{1 2}

Al-Juwayni reports that al-Qadi argued that the Book and the sunna are received with acceptance, consensus joins them, and analogy based on consensus relies on an agreed base, whereas inference has no base to attest it; and that if meanings are not bounded by bases they cannot be controlled, and the law reverts to following opinion and the wisdom of sages, varying with time, place and kinds of people. ²

Al-Juwayni reports that al-Shafi'i argued that we know for certain that no event lacks a ruling of God; that the earlier imams left no event, for all the multitude of questions, without a ruling; and that if the sources of rulings were confined to the texts and their meanings, ijtihad would not have its breadth, since these are only "a handful from the sea" of the law. ³ He supported this by noting that the Companions in their consultations did not first set up a base and then draw out a meaning, but reasoned without regard to bases. ^{3 4} Al-Juwayni says anyone who follows al-Shafi'i's reasoning finds him attaching rulings to unattested meanings, and turning to bases by way of resemblance only when these are lacking. ⁴

Al-Juwayni holds that al-Qadi's objection - loss of control and handing matters to the opinions of the wise - applies only to Malik and his circle "if what is reported of him is sound"; he argues that if every opinion could be followed without closeness, a wise man versed in governance could act on what seemed soundest to him wherever there is no text - "a hard mount no religious person would dare ride", since opinions vary with regions and times. ^{4 5}

The Malikis' own account of their doctrine of unattested interests, from their books, and the rest of the chapter on al-Shafi'i's conditions (p. 679 onwards) are not given here.