Why Divergence Isn't a Bug
The Quran fixes many inheritance shares explicitly — a son takes double a daughter's share, a spouse takes 1/4 or 1/8 depending on children, and so on. But it doesn't resolve every combination of surviving heirs by name, and the Sahaba and the classical jurists who came after them didn't always reach the same answer when they filled those gaps. That's where the six schools genuinely diverge — not on the plain Quranic text, but on how to resolve the cases it leaves open. Six named classical cases show exactly where and why: this is what Wasiyat's calculation engine has to get right, per doctrine, on every single family it processes.
The 'Awl Origin Case — a Husband and Two Sisters
A husband survived by two full sisters and no closer heirs presents a genuine problem: the Quranic shares add up to more than the whole estate. The husband's fixed 1/2 plus the sisters' fixed 2/3 (as joint residuary-equivalent heirs) sum to 7/6 — one-sixth over. The four Sunni schools and Ahle Hadees follow the resolution first applied during Umar ibn al-Khattab's (RA) caliphate: 'awl, a proportional abatement of every share by the same ratio. The husband's 1/2 becomes 3/7; each sister's 1/3 becomes 2/7. The Ja'fari school rejects 'awl outright — a Quranic share, once fixed, is never reduced. The husband keeps his full 1/2, and the two sisters absorb the entire 1/6 shortfall between them, landing at 1/4 each instead of the 2/7 a Sunni calculation would give them.
Gharrawayn — the Two 'Umariyyatayn' Cases
Gharrawayn (“the two dazzling cases”) arise when a spouse and both parents survive together, with no children. Read the fixed shares literally and the mother would take 1/3 of the whole estate — more than the father in some configurations, which conflicts with the Quranic principle that a male heir takes double a female heir's share in equivalent standing (Surah An-Nisa 4:11). The four Sunni schools and Ahle Hadees follow Umar's resolution: the mother takes 1/3 of the remainder after the spouse's share, not 1/3 of the whole — so with a husband, mother, and father surviving, the split is husband 1/2, mother 1/6, father 1/3; with a wife, mother, and father, it's wife 1/4, mother 1/4, father 1/2. Either way the father ends up with exactly double the mother, preserving the 2:1 ratio. The Ja'fari school does not apply this adjustment — the mother takes her full 1/3 of the whole estate regardless, which inverts the father's position: 1/6 in the husband-mother-father case, or 5/12 in the wife-mother-father case.
Radd — When the Fixed Shares Fall Short
Radd is the mirror problem to 'awl: sometimes the fixed Quranic shares don't exhaust the estate, and there are no residuary heirs left to absorb the rest. A mother and a single daughter, for instance, are entitled to a fixed 1/6 and 1/2 — two-thirds of the estate, with a third left over and nobody else to claim it. The classical Shafi'i and Maliki position escheated that surplus to the public treasury (bayt al-mal); the Hanbali and Ja'fari schools returned it proportionally to the existing sharers. Where no functioning bayt al-mal exists to receive an escheat — which describes India — the prevailing modern Shafi'i and Maliki position converges with Hanbali and Ja'fari practice: the surplus is returned pro-rata. In this example, that lands the mother at 1/4 and the daughter at 3/4.
Tabaqat vs. 'Asaba — the Ja'fari Class System
A sole surviving daughter and the deceased's full brother produce one of the sharpest splits between the traditions. The Sunni schools treat the daughter's fixed 1/2 share and the brother's claim as residuary ('asaba) heir side by side — daughter 1/2, brother 1/2. The Ja'fari school instead groups all possible heirs into three ranked classes (tabaqat): children and parents in Class I, siblings and grandparents in Class II, and more distant relatives in Class III. Any surviving heir in a higher class excludes the entire lower class outright — not just reduces their share, excludes them completely. Here, the daughter's presence in Class I excludes the brother in Class II entirely: she takes the full estate (her fixed 1/2 plus the remaining 1/2 by radd), and he receives nothing.
Muqasama — the Paternal Grandfather's Floor
When a paternal grandfather inherits alongside full brothers (and no father, since a living father would exclude the grandfather entirely), the Shafi'i, Maliki, and Hanbali schools, along with Ahle Hadees, apply muqasama — the grandfather is treated as sharing alongside the brothers as if he were one of them, but with a guaranteed floor of never taking less than 1/3 of the estate. With one brother, sharing as an equal gives the grandfather 1/2, so muqasama applies and he takes 1/2, matching the brother. With three brothers, sharing equally would only give him 1/4 — below the floor — so the 1/3 floor takes over instead: the grandfather takes 1/3, and the three brothers split the remaining 2/3 at 2/9 each.
Al-Minbariyya — 'Ali's Pulpit Case'
Named for the case famously decided from the pulpit (minbar), this scenario involves a wife, both parents, and two daughters — a five-heir combination that produces another 'awl situation, more severe than the origin case. The wife's 1/8, the parents' 1/6 each, and the daughters' combined 2/3 sum to 27/24 nominally. The Sunni schools and Ahle Hadees abate the whole base from 24 to 27, which is where the case gets its second name — "her eighth became a ninth": the wife's fraction, expressed against the new base, works out to exactly 1/9. Father and mother each take 4/27, and the two daughters split 16/27 between them at 8/27 each. The Ja'fari school, consistent with its rejection of 'awl elsewhere, keeps every fixed share exactly as written — the wife keeps her full 1/8 — and lets the two daughters alone absorb the entire shortfall, landing at 13/48 each instead of 8/27.
Why the School You Choose Actually Matters
These aren't edge cases invented to make a point — husband-and-sisters, spouse-and-both-parents, and mother-and-daughter are ordinary family configurations that show up constantly in real estate planning. As the six cases above show, the same surviving family can produce meaningfully different distributions depending on which school of thought applies, sometimes by a matter of a few percentage points, sometimes — as in the Tabaqat case — by the entire estate changing hands. Wasiyat's calculation engine runs the classical rules for whichever of the six schools you select, verified against golden test vectors built from primary sources including Muwatta Malik, Sistani's Islamic Laws, and Mughniyya's comparative fiqh, so the doctrine you choose is applied precisely rather than approximately.