Why are there ten accepted ways of reciting the same Quran?

The Quran was passed on by voice before it was fixed on parchment, and the early written text was only a skeleton: it did not mark vowels, and it did not always tell similar-looking consonants apart. A skeleton like that can be read, with a little variation, in more than one way. The different accepted ways are called qira'at, "readings".

By tradition there are ten recognised schools, each named after a noted reciter, such as Nafi' al-Madani or 'Asim. In the 10th century a Baghdad scholar, Ibn Mujahid, picked seven readers from Mecca, Medina, Kufa, Basra and Damascus; later Ibn al-Jazari added three more to make ten. To count as accepted, a reading had to fit the written skeleton of the Uthmanic codex, be consistent with Arabic grammar, and have an authentic chain of transmission.

The differences can touch vowels, consonants and even whole words, but they are often subtle, and they are described as not changing the overall message or doctrinal meanings. Today the most popular readings are those transmitted by Hafs (from 'Asim) and by Warsh (from Nafi'), and the 1924 Cairo edition, in general use across almost the whole Muslim world, is based on Hafs.

Differences in recitation appear in the tradition itself. In a hadith, Umar hears Hisham reciting a surah in a way he thinks is incorrect, manhandles him and hauls him to Muhammad. Each of them recites, and each time Muhammad says, "It was revealed thus." Then he adds that the Quran was revealed in seven "ahruf", a word scholars have explained in different ways.