On seeing someone fidgeting during prayer, Umar said:

“Had this man’s heart been humbly submissive, his limbs would have been likewise.”

A hadith states:

“A servant’s faith will not be upright until his tongue is upright, and his tongue will not be upright until his heart is upright.”

Thus, outward conduct is a necessary consequence of the inward state in one respect, and entails it in another. It serves as evidence of the inward state insofar as it entails it, not insofar as it is its necessary consequence. For evidence entails what it indicates: the existence of the evidence necessarily implies the existence of what it indicates, whereas the existence of a thing does not necessarily imply the existence of evidence indicating it. Evidence holds in the forward direction, but not in reverse, whereas a definition holds in both directions.

They disagreed over whether a cause must invariably hold, such that an exception or counterexample invalidates it. The correct position is that the term “cause” may refer to the complete cause—the totality of what necessarily entails the ruling. In this sense, it must invariably hold. The term may also refer to a factor that gives rise to the ruling, but whose efficacy depends upon the fulfilment of conditions and the absence of impediments. In this sense, if the ruling fails to follow from it for any other reason, the cause is invalidated.

They likewise disagreed over whether it must hold in reverse—that is, whether the absence of the ruling necessarily implies the absence of its cause.

Some said:

“It need not hold in reverse, since a ruling may have two causes.”

Others said:

“It must hold in reverse, because whenever the ruling is established in the absence of that cause, the cause has no effect upon it. Rather, the ruling is independent of it, and the absence of any effect invalidates the cause.”

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