the apparent position of Ahmad, the more authentic of the two views reported from him, and the view of most of his followers—is that knowledge, reason, and similar qualities admit of increase and decrease. Indeed, the same applies to qualities found in nonliving things, such as colours, tastes, and scents.
We begin, then, by saying that a decisive will is one that necessarily results in action when the ability to act is present. Whenever decisive will and full ability are both present, the action must occur, since the cause is fully present without any countervailing impediment. Whenever will and full ability are present but the action does not occur, the will is not decisive. This describes the will of created beings to perform actions that they are capable of performing but do not perform, although such willing varies greatly in strength and weakness. Yet wherever the intended action does not occur despite full ability, the will is not completely decisive.
Disagreement over this “question” has become widespread only because people have supposed that there can be a decisive will to act without any accompanying action whatsoever. This cannot occur. It can occur only with a resolve to act: someone may resolve to perform an action in the future without doing any part of it in the present. Resolving to act in the future is not sufficient to bring the action about. Rather, when the action occurs, the will must become complete in a way that necessarily entails the action. This is decisive will.
When a person has “decisive will” and does whatever lies within his ability, he is regarded under Islamic law as equivalent to someone who performs the action in full: he receives the reward, and incurs the punishment, of the person who performs it in full