This has given rise to the division of the whole book into literal and allegorical statements. In order to explain these correctly the commentator must know (1) the reason why, (2) the place where, (3) the time when, the particular passage he is expounding was revealed; he must know whether it abrogates or is abrogated, whether it is in its proper order and place or not; whether it contains its meaning within itself or needs the light which the context throws upon it; he must know all the Traditions which bear upon it, and the authority for each such Tradition. This effectually confines the order of commentators in the strict sense of the word to the Companions, and supplies the reason why commentators since then simply reproduce their opinions.[52] But to return from this digression. Sentences are Zahir--"Obvious," or Khafi--"Hidden." Obvious sentences are divided into four classes. I. (1). _Zahir_, or obvious, the meaning of which is so clear that he who hears it at once understands its meaning {50} without seeking for any explanation. This kind of sentence may be abrogated. Unless abrogated, action in accordance with it is to be considered as the express command of God. All penal laws and the rules regulating the substitution of one religious act for another, _e.g._ almsgiving instead of fasting, must be based on this, the clearest of the obvious sentences. (2). _Nass_, a word commonly used for a text of the Quran, but in its technical meaning here expressing what is meant by a sentence, the meaning of which is made clear by some word which occurs in it. The following sentence illustrates both Zahir and Nass: "Take in marriage of such other women as please you, two, three, four." This sentence is Zahir, because marriage is here declared lawful; it is Nass, because the words "one, two, three, four," which occur in the sentence, show the unlawfulness of having more than four wives. (3). _Mufassir_, or explained. This is a sentence which needs some word in it to explain it and make it clear. Thus: "And the angels prostrated themselves, all of them with one accord, save Iblis (Satan)." Here the words "save Iblis," show that he did not prostrate himself. This kind of sentence may be abrogated. (4). _Mukham_, or perspicuous. This is a sentence as to the meaning of which there can be no doubt, and which cannot be controverted, thus: "God knoweth all things." This kind of sentence cannot be abrogated. To act on such sentences without departing from the literal sense is the highest degree of obedience to God's command. The difference between these sentences is seen when there is a real or apparent contradiction between them. If such should occur, the first must give place to the second, and so on. Thus Mukham cannot be abrogated or changed by any of the preceding, or Mufassir by Nass, &c. The other great division of sentences is that of