Ilhaq (attaching one thing to another: analogy, lineage, and accessories)

Ilhaq in the lexical sense is following: "I attached him to it" means I made him follow it until he caught up. Jurists and usulis use it for attaching branches to roots in analogy, and on its own it usually refers to the ascription of a child's lineage. ¹

• Analogy: attaching a branch to a root by a common cause, so that the ruling passes across on its conditions. ²
• Ascribing a person of unknown lineage to the one who claims him, on the conditions stated under lineage. ²

The first removes the difference that bears on the ruling, so that the unmentioned case is covered without naming the cause; scholars differ on whether this is called analogy. The second names the common cause and shows that it exists in the branch, and this is agreed to be analogy. ²

• The fetus of a slaughtered animal joins its dam if it is fully formed and dies at the dam's slaughter; this is the view of the Malikis, Shafi'is, Hanbalis and the two companions of Abu Hanifa, citing "the slaughter of the fetus is the slaughter of its dam". Abu Hanifa and Zufar disagree and require that the fetus be found alive and slaughtered. ²³
• Young livestock join the adult in zakat when they are with them and a year passes; if all are young, the jurists differ. ³
• Accessories of a sale: the fetus follows its dam in sale and is not sold alone; the right of way and watering rights follow land; a calf of a milk cow follows its dam; trees follow the land. ³

Ilhaq is treated under analogy, under sale (joining fruit to the tree, and unripe fruit to ripe), under lineage, and under religion when the parents differ in faith. ³