the Book and Sunnah. However, knowledge beyond what a particular individual needs is a collective obligation: if a group fulfils it, the rest are relieved of it.

As for “knowledge whose pursuit is encouraged in general,” this is the knowledge that the Prophet, may Allah bless him and grant him peace, taught his community. Each person, however, is encouraged to pursue the knowledge he needs most and that benefits him most, and this varies. For people in general, seeking to learn about obligatory and recommended deeds, promises of reward, and warnings of punishment is more beneficial. Each person seeks whatever he needs of these matters. If a doubt arises in someone’s heart, pursuing an action that counters it may be more beneficial to him than anything else.

As for “certainty,” it is the tranquillity of the heart and the firm establishment of knowledge within it. This is the sense conveyed by the expression mā’ yaqan (“still water”), used when water has ceased moving. The opposite of certainty is doubt, which is a kind of movement and agitation. Thus one says rābanī, yarībunī (“it disturbed me; it disturbs me”). The same usage occurs in the hadith:

“The Prophet, may Allah bless him and grant him peace, passed by a gazelle curled up asleep and said, ‘Let no one disturb it.’”

Certainty thus encompasses two things: the heart’s knowledge and the heart’s actions. A servant may know something with absolute conviction, yet his heart may still experience unrest and agitation in connection with the action that this knowledge entails. For example, a servant knows that Allah is the Lord and Sovereign of everything; that there is no creator besides Him; and that whatever He wills happens, and whatever He does not will does not happen. This knowledge may be accompanied by tranquillity in turning to Allah and reliance upon Him, or it may not be accompanied by acting accordingly. This may be because the heart is heedless of this knowledge—heedlessness is the opposite of complete knowledge, though not of knowledge at its most basic level—or because thoughts arise in the heart that turn its attention to causes, or for some other reason.