Among them is a type in which both the written form and the meaning change, such as the verse
“and clustered banana-trees” (wa ṭalḥin manḍūdin)
and the alternative reading
“and clustered date-spadices” (wa ṭalʿin manḍūdin).

Another type involves transposition, as in the verse
“And the agony of death has come in truth”
versus the rendering
“and the agony of truth has come with death.”

Another category is that of addition and omission, for example:
“ninety-nine female sheep,”
“As for the boy, he was a disbeliever while his parents were believers,”
and
“surely Allah, after their being coerced, is to them All-Forgiving, Most Merciful.”

Fifth opinion
Some have said that the seven aḥruf are the thematic divisions of the Book of Allah—command, prohibition, promise, threat, narration, disputation, and parable. Ibn ʿAṭiyyah judged this weak, arguing that such matters are not called “letters,” and that there is consensus that the dispensation granted did not pertain to declaring something lawful or altering any meaning. Qāḍī Ibn al-Ṭayyib cited a ḥadīth of the Prophet—peace and blessings be upon him—supporting this interpretation, then added: “But these are not the readings the Prophet permitted; rather, in this context ḥarf means ‘direction’ or ‘method,’ as in the verse, ‘And among the people is he who worships Allah upon an edge (ḥarf)’ (Q 22:11). Accordingly, the ḥadith means: on seven ways having to do with lawful, unlawful, and the like.”

It has also been said that the Prophet’s words, “The Qur’an was revealed according to seven aḥruf,” refer to the seven canonical readings transmitted by the Seven Readers, since all of those readings are soundly traced back to the Messenger of Allah—peace and blessings be upon him. This view, however, is untenable, as will become clear.

Section

[Statement of many scholars that the seven canonical readings are not the seven aḥruf]
Many of our scholars—such as al-Dāʾūdī, Ibn Abī Ṣufrah, and others—have maintained that the seven readings attributed to the Seven Readers are not the seven aḥruf within which the Companions enjoyed latitude when reciting. Rather, they all belong to a single ḥarf of those seven, namely the one upon which ʿUthmān compiled the muṣḥaf; Ibn al-Naḥḥās and others have reported this. The well-known readings are merely the personal selections of those master-reciters: each of them, from the corpus he had received and understood, chose what he deemed best and most fitting, adopted it as his method, taught it, and became famous for it, so that it was said, “the reading of Nāfiʿ,” “the reading of Ibn Kathīr,” and so forth. None of them forbade or disavowed the choice of another; rather, each regarded the other’s reading as permissible. From every one of these seven Imams there have been transmitted two or more chosen paths, all of them sound. Throughout these later centuries the Muslims have unanimously relied on whatever has been authenticated from those Imams—what they narrated, transmitted, and wrote of the Qur’anic readings.