They fail to observe the fact that rational principles cannot be thus restricted...

They fail to observe the fact that rational principles cannot be thus restricted, and that in cases of voluntary action, the will of the agent is one of the parts of the complete cause, and as long as there is no will to carry out the voluntary action, the complete cause is not realized, even if all the other conditions of existence and nonexistence should obtain.

The conclusion is that every cause, complete or incomplete, has relative necessity ( wujūb bil-qiyās ) in relation to its effect, and similarly every effect has relative necessity in relation to its complete cause, and these two points may be together referred to as ‘the rule of mutual implication of cause and effect.’ The Simultaneity of Cause and Effect From the principle of the mutual implication of cause and effect other principles may be derived, among which is the principle of the simultaneity of cause and effect, which may be described as follows.

Whenever an effect is a temporal existent and at least one of the parts of its complete cause is also temporal, the cause and effect will occur simultaneously, and the occurrence of the complete cause will have no temporal distance from the effect.

For if it is supposed that some time, no matter how short, elapses after the occurrence of all the parts of the complete cause and the effect occurs after that, this would imply that the existence of the effect is not necessary at that very supposed time, while the implication of the relative necessity of the effect in relation to the complete cause is that the existence of the effect becomes necessary as soon as the cause is complete.

However, this principle does not apply to incomplete causes, for the existence of the effect will not be necessary with the existence of any of them. Rather, even if just one of the parts of the complete cause is absent, the existence of the effect will be impossible, for otherwise the effect would not need the said part. However, if the cause and effect are immaterial, and neither of them is temporal, in that case their temporal simultaneity would be meaningless.

The same goes for the case in which the effect is temporal but the cause is completely immaterial, for the meaning of temporal simultaneity is that two existents occur at the same time, while something completely immaterial does not occur in the temporal realm, and has no temporal relation to any existent.