As for the first kind of capacity, if it did not exist, moral responsibility itself could not be affirmed, as is evident from His words, “So fear Allah as much as you are able” (Q 64:16) and “Those who believe and do righteous deeds—We burden no soul beyond its capacity” (Q 7:42), and similar verses. People who have been negligent and gone to excess in the fundamentals of the religion—when they find themselves unable to listen to what has been revealed to the Messenger—belong to this category.

They have likewise differed over a commanded act that Allah knows will never take place, or has informed us will never take place. Some claim that such an act lies outside human power. The extreme Qadariyyah even deny that Allah’s prior knowledge, statement, or scripture could precede the fact that the act will not occur. Both of these groups agree that whatever contradicts Allah’s foreknowledge is neither possible nor within anyone’s power.

The majority of scholars opposed them, arguing that this position is invalidated by Allah’s omnipotence. Allah knows each matter exactly as it is: He knows that the act is in principle possible and within the servant’s ability, yet it does not occur because the servant does not will it, or because he dislikes it, and so forth—not because he is incapable of it. This whole debate is resolved once we distinguish the two kinds of capacity, as explained earlier: the act is indeed impossible when measured by the capacity that must accompany the deed itself, but it remains possible with respect to the validating capacity that underlies every command and prohibition.

As for the second type of incapacity, everyone agrees that a person who is physically unable to act simply cannot do so, just as a blind man, an amputee, or a paralytic cannot add diacritical marks to, or copy, a Qur’anic codex, nor can he fly. All concur that this sort of case never falls under the Law’s demands.