08 — The Grandfather and Siblings: the Full Muqasamah System

The hardest chapter in classical faraidh, and the main reason this bundle exists: the grandfather inherits together with full or paternal half-siblings. At-Tahqiqat al-Mardhiyyah dissects it at length as part of the madhhab system; at the end of the chapter, al-Fawzan’s own preferred opinion (tarjih) (pp. 135–140) is stated plainly.

What the dispute is about

If the deceased leaves a grandfather and full or paternal half-brothers/sisters with no father present, there are two major opinions among the Companions:

1. The grandfather is like the father → all siblings are excluded (Abu Bakr, Ibn Abbas, and a dozen-plus Companions; the Hanafi madhhab; chosen by Ibn Taymiyyah, Ibn al-Qayyim, and in modern times Ibn Baz, Ibn Uthaymin, and al-Fawzan himself).
2. The grandfather shares with the siblings (muqasamah) → the opinion of Ali, Ibn Mas’ud, and Zayd ibn Thabit; it became the official position of the Maliki, Shafi’i, and Hanbali madhhabs — the system used by the majority of textbooks, curricula, and inheritance courts, and the one at-Tahqiqat teaches in full.

This chapter teaches how to calculate under the muqasamah system — because without mastering it you cannot read any faraidh textbook, verify a madhhab-based inheritance ruling, or understand where the bases 18 and 36 come from.

Situation 1: grandfather + siblings only (no other fixed-share heirs)

The grandfather takes whichever is better of two options:

• Muqasamah — calculated as if he were one brother (2 heads; a sister counts as 1 head), or
• 1/3 of the whole estate.

The math is clean: with h = the number of sibling heads, the grandfather’s share via muqasamah = 2/(2+h). That is greater than 1/3 as long as h < 4:

Situation 2: other fixed-share heirs are present

The grandfather takes whichever is best of three: muqasamah of the remainder, 1/3 of the remainder, or 1/6 of the whole estate — and no matter what, the grandfather never gets less than 1/6 (if the fixed shares exhaust the estate, he is still given 1/6, resorting to ‘awl if needed).

It is precisely this “1/3 of the remainder” fraction that gives rise to bases 18 and 36 (chapter 06): 1/3-of-the-remainder on a base of 6 requires 18, on a base of 12 requires 36.

A sister alongside the grandfather

A sister (full or paternal half) does not receive a fixed share alongside the grandfather — she only takes part in the muqasamah (grandfather : sister = 2 : 1). The one exception is al-Akdariyyah, below.

Al-Mu’addah: paternal half-siblings still counted

If both full siblings and paternal half-siblings are present, the full sibling(s) include the paternal half-sibling(s) in the head count against the grandfather (shrinking the grandfather’s muqasamah share), then take back the paternal half-sibling’s portion — because a full sibling excludes a paternal half-sibling.

Example: grandfather + 1 full sister + 1 paternal half-brother. Heads = 2 + 1 + 2 = 5 → grandfather’s muqasamah share is 2/5 (better than 1/3). Of the remaining 3/5: the full sister takes up to her ceiling of 1/2 of the estate (5/10), and the excess (3/5 − 1/2 = 1/10) then falls to the paternal half-brother. Final: grandfather 4/10, full sister 5/10, paternal half-brother 1/10.

Al-Akdariyyah (“the muddying case”)

Composition: husband + mother + grandfather + 1 full sister (or paternal half-sister). The one and only case where a sister is given a fixed share alongside the grandfather, and the one and only ‘awl in the grandfather chapter:

1. Base 6: husband 1/2 = 3, mother 1/3 = 2 (only one sibling present), grandfather 1/6 = 1, sister 1/2 = 3 → total 9 → ‘awl 6 → 9.
2. Then the grandfather’s and sister’s shares are pooled (1 + 3 = 4) and redivided 2 : 1 → 4 does not divide by 3 → ×3 → base becomes 27.
3. Final: husband 9, mother 6, grandfather 8, sister 4.

Worked in full with figures in chapter 11’s case studies.

flowchart TB
  classDef proses fill:#713f12,stroke:#ca8a04,color:#fef9c3
  classDef furud fill:#1e3a8a,stroke:#3b82f6,color:#dbeafe
  classDef khilaf fill:#7f1d1d,stroke:#ef4444,color:#fee2e2
  classDef hasil fill:#3b0764,stroke:#a855f7,color:#f3e8ff
  A["Grandfather meets siblings<br/>(no father present)"]:::khilaf --> B{"Which opinion to follow?"}:::proses
  B -- "al-Fawzan's, Ibn Uthaymin's,<br/>Ibn Baz's tarjih: grandfather = father" --> C["Siblings EXCLUDED<br/>calculate as usual"]:::hasil
  B -- "madhhab (Maliki/Shafi'i/Hanbali):<br/>muqasamah" --> D{"Other fixed-share<br/>heirs present?"}:::proses
  D -- no --> E["Grandfather: best of<br/>muqasamah vs 1/3 of estate"]:::furud
  D -- yes --> F["Grandfather: best of muqasamah ·<br/>1/3 of remainder · 1/6 of estate<br/>(minimum 1/6)"]:::furud
  F --> G["Special case:<br/>al-Akdariyyah ('awl 9 → 27)"]:::khilaf

Al-Fawzan’s tarjih — and this bundle’s stance

After laying out the system above, al-Fawzan affirms the first opinion: siblings are excluded by the grandfather just as they are excluded by the father (at-Tahqiqat al-Mardhiyyah, pp. 135–140; confirmed by IslamQA 240582, which places him alongside Ibn Baz and Ibn Uthaymin in this camp). In practice: master both — muqasamah to read the textbooks and verify madhhab-based rulings, and the tarjih to know which way the verifying scholars (muhaqqiqun) lean. For any real-world division, pick one line and stay consistent (chapter 13).

Sources: at-Tahqiqat al-Mardhiyyah, chapter on the inheritance of the grandfather with siblings (pp. 135–140 for the tarjih); IslamQA 240582; al-Mulakhkhash al-Fiqhi (Shamela 11811). Full list in 15-references.