Suitability (munasaba) as a ground of legal cause

In the lexicon munasaba is suitability. In usul, following Ibn al-Hajib, it is an apparent and definable attribute whose connection with a ruling is grasped by reason, and whose effect is a benefit or the averting of a harm. ^{1 2}

It is one of the rational ways to establish a cause, called also ilkhala, maslaha, istidlal or regard for the purposes; drawing it out is called takhrij al-manat. ¹

Imam al-Haramayn argued from the Companions' practice of joining unmentioned cases to mentioned ones when they judged them alike. ^{1 2}

The real suitability is one that does not fall away on reflection; persuasive suitability is the rest. Real suitability is of three grades: necessity, need and refinement. ²

The first kind is what the lawgiver disregards, and reasoning from it is forbidden, as with the two-month fast for intercourse in Ramadan, which the law puts ahead of freeing a slave. The second is what the law upholds. The third is what neither upholds nor disregards: the public interest without a text. ²

The effective ground is one whose effect on the ruling is shown by text or consensus; the fitting ground is one the law upholds without text; the strange ground is one whose connection with the ruling is found without the kind being upheld, as with barring a divorced wife from inheriting in terminal illness. ^{3 3}