the suitability of an effective cause is undermined by a countervailing consideration, and whether an impediment opposing a causative factor negates it or not, in respect of its causal efficacy while the factor itself remains.

To clarify the nature of this disagreement: the term “effective cause” may mean the complete cause—the totality of what necessarily entails a ruling, such that whenever it exists, the ruling exists without fail. In this usage, the term includes what completes the cause, its conditions, and the absence of any impediment. According to one view, this is because the absence of an impediment necessarily entails a positive attribute; according to another, it is because an absence may form part of what completes the causative factor. Whenever such a cause admits an exception and is invalidated, with the ruling existing without it, this demonstrates its unsoundness.

For example, if someone explained the shortening of prayer by the mere existence of an excuse, he would be told:

“This is incorrect. The sick and others with valid excuses do not shorten their prayers; only travellers do so. Thus, shortening prayer accompanies travel, being present when travel is present and absent when it is absent.” When a ruling accompanies an attribute in both its presence and its absence, this indicates that the attribute is what the ruling depends upon. Likewise, if someone explained the obligation of zakat by the mere possession of the minimum threshold of wealth, he would be told: “This is disproved by possessing that wealth before a year has elapsed.”

The term “effective cause” may also mean that which calls for a ruling, even though the ruling depends upon certain conditions being fulfilled and impediments being absent.

This may also be expressed by the term “cause,” as when it is said:

“The causes establishing entitlement to inheritance are