Prayer is divided initially, and as a whole, into two kinds: obligatory and recommended. The discussion covering the principles of this form of worship is confined to four categories, that is, four parts. Part One is about the identification of the obligation and matters related to it. Part Two is about the identification of its three conditions: the condition of obligation, condition of validity, and the condition of completion. Part Three covers the identification of its acts and words, and these are its essential elements (arkan). Part Four is about its delayed performance and the identification of forms of rectification following irregularity, for it is the delayed performance of an act that would not be deemed as lapsed had it been duly performed.