it does not occupy itself with another act opposed to the first, for it cannot be devoid of all movement and stillness. On this basis, al-Ka'bī denied the existence of “the permissible” in the revealed Law: every permissible act occupies a person to the exclusion of a forbidden act; refraining from the forbidden is obligatory, and one cannot refrain from it without engaging in its opposite. This permissible act is its opposite. A command to do something entails a prohibition of its opposite, while a prohibition entails a command to do its opposite if it has only one opposite; otherwise, it entails a command to do one of its opposites. Thus, whichever opposite a person engages in becomes obligatory, as an obligation allowing a choice among alternatives.

This objection of al-Ka'bī perplexed many theoretical scholars. Some, such as Abū al-Hasan al-Āmidī, admitted that they could not answer it. Others, such as Abū al-Ma'ālī, lent it support on the premise that prohibiting something entails commanding its opposite. Still others said: This applies when its opposites are limited in number. When they are not limited in number, prohibiting it does not entail commanding any one of them. This resembles the distinction between an unrestricted obligation and an obligation allowing a choice among alternatives. In the latter case, it is said that the command requires one of the three alternatives; in the former, that it requires the element common to them. Our grandfather, Abū al-Barakāt, inclined toward this view.

They also challenged al-Ka'bī with the case of someone who avoids one forbidden act by committing another. He might, however, reply: A person must abandon all forbidden acts in favour of something that is not forbidden—whether permissible, recommended, or obligatory.