Overlap of causes and rulings (tadakhul)

Tadakhul is one thing entering another without any addition in size. In the jurists' usage, several causes may be met by a single ruling, or several rulings by a single act. The schools differ on whether it operates in causes or in rulings. ^{1 2}

In Arabic, tadakhul is similarity and confusion of matters and one entering another; in arithmetic, two numbers overlap when the smaller measures the greater, as three and nine. ¹

• Indirajj: one matter entering a broader one, such as the minor impurity within major impurity. ¹
• Tabayun (contrast): two things that share nothing, against overlap, which applies among similar things. Tamathul (sameness) and tawafuq (agreement by a third number) are also distinguished. ²

The Hanafis hold that overlap is in causes or in rulings. It fits acts of worship better in causes and penalties better in rulings, since penalties are averted by doubt. ^{2 5} Al-Qarafi of the Malikis placed it in causes, not rulings; al-Zarkashi placed it in rulings, not causes. ⁵ Examples: repeated recitation of a verse of prostration in one sitting needs only one prostration (Hanafi); one who commits unlawful intercourse, then again before being punished, receives one penalty. ⁵

Where the causes of ghusl recur, such as menstruation and janaba, or two instances of janaba, the Hanafis and Malikis hold that one ghusl suffices. When wudu and ghusl both fall due, the Shafi'is and Hanbalis have several views, from a single ghusl sufficing to both acts overlapping in actions but not in intention. ^{3 6}

The greeting of the mosque is covered by the obligatory prayer in the view of Ibn Najim and al-Qarafi; the Hanbalis hold it is covered by the obligatory and the regular sunna prayers. ⁶ In prostration for forgetfulness, two prostrations suffice for several lapses of one kind, a view the Shafi'is and most Hanbalis hold, while others require two for each kind. In recitation prostration, the Hanafis require one for repeated recitation at one sitting; the Malikis require each recurrence except for teacher and taught; the Shafi'is have three views. ^{7 8 9}

Al-Qarafi holds that the fast of i'tikaf falls within the Ramadan fast, since i'tikaf is a cause for the command to fast, and sighting the crescent is another cause. ⁹ One who combines hajj and umra in a single state of ihram needs one circuit and one running according to the Malikis, Shafi'is and one narration of Ahmad, and two according to the Hanafis and another narration of Ahmad. ^{9 10}

Ransom overlaps in the Hanafi and Shafi'i schools for prohibited acts within one sitting; Abu Hanifa and Abu Yusuf hold that each hand and foot requires its own ransom when the sittings differ. ^{10 11} For intercourse in a day of Ramadan, one expiation suffices according to Muhammad ibn al-Hasan and one narration of Ahmad; the majority require two for two days. ¹¹ Expiations for several oaths overlap according to one view in the Hanafi school, and do not overlap for the Malikis and Shafi'is. ¹²

Two waiting periods of one kind for one man overlap according to the Hanafis, Shafi'is and Hanbalis; for two men the Hanafis let them overlap, the Shafi'is and Hanbalis do not, since each is a right owed to a person. ^{12 13} Ibn Juzayy sets out the Maliki cases: a woman under a revocable divorce whose husband dies moves to the waiting period for death. ¹³

Injuries to the person and to limbs overlap in some cases according to the Hanafis; for the Malikis a limb injury enters the retaliation for death when the injurer intended it. Among the Hanbalis there is overlap in one narration. Blood-money overlaps when the smaller sum falls within the greater, such as the sum for a limb within the full blood-money. ^{13 14 15}

The jurists agree that penalties of one kind and one cause overlap: repeated unlawful intercourse brings one penalty. For slander and wine-drinking, which share the same measure, the Malikis hold them overlapping. Where a penalty of death is among them, the Hanafis, Malikis and Hanbalis suffice with it. ^{15 16} Abu Hanifa holds that the jizya for several years overlaps; the Shafi'is, Hanbalis, Abu Yusuf and Muhammad hold it does not. ^{16 4}

When the larger of two numbers is exhausted by the smaller when subtracted twice or more, the two overlap; the larger is then taken as the base of the problem. When they agree by a third number, they are in agreement and the product of one's agreed part and the other gives the base; when they share no common measure, one multiplies one by the other. ⁴