I have also written in my treatment of “Covenants and Contracts”—on religious covenants among the general principles, and on worldly contracts among the principles of jurisprudence—and in the Book of Vows, that when something is already obligatory under Islamic law, and a servant vows to perform it, makes a covenant with Allah to do so, pledges himself to the Messenger or the ruler to do so, or joins others in a mutual oath to do so, these covenants and solemn pledges impose a second obligation, distinct from the obligation established by the original command alone. The act thus becomes obligatory on two grounds: whoever neglects it deserves both the punishment due to someone who breaks a covenant or solemn pledge and that due to someone who disobeys Allah and His Messenger. This is the correct analysis.

Some jurists of Ahmad’s school say that when someone vows to perform an obligatory act, its status remains unchanged after the vow, unlike a vow to perform a recommended act. This is not correct. If a vow makes a recommended act obligatory, then it is all the more capable of imposing an obligation to perform an already obligatory act. This does not amount to bringing about what already exists. Rather, these are two obligations of different kinds, each with a legal effect distinct from the other. An example is a grandmother who is both one’s maternal grandmother’s mother and one’s paternal grandfather’s mother: she possesses two grounds of entitlement, each of which entitles her to one-sixth.

Likewise, some jurists of Ahmad’s school say that conditions inherent in a contract cannot validly be stipulated, or may even invalidate it. Some jurists of al-Shāfiʿī’s school have gone so far as to say that if someone says, “I give her to you in marriage on the terms Allah has commanded—keeping her on honorable terms or letting her go with kindness,” the marriage is invalid because he has stipulated divorce within it. This is