Many Muslims try to capitalize in their debates on the fact that there are variant readings of Biblical text in the many manuscripts we have of it. This is natural for handcopied texts and nothing else can be expected. Just try yourself to copy down by hand twenty pages of any book, then let a friend proofread it and see how many mistakes he finds. It is humanly nearly impossible to copy by hand without any error. In a certain sense Muslims have the "advantage" that Christians have carefully documented these variants in scholarly journals and monographs. Christian and secular scholars are openly discussing these problems in the discipline of textual criticism.
On the other hand, Muslim have the well known propaganda statement that there are no variants in the Qur'an at all and the Qur'an has been the same text even to the detail of each single letter and that this was so from the very beginning. More educated Muslims know that this is not true, but the average Muslim is made to believe this objectively wrong claim.
In particular, let us ask why some of the oldest manuscripts are not photographically reproduced and made available to the public and the scholars. Why not start with the Topkapi manuscript in Istanbul, the Taschkent manuscript, and the two old manuscripts in Cairo and Damascus. They are not Uthmanic manuscripts as some believe, but they are quite old. And then, publish them together in a format that makes it easy to compare them, or even better, listing all the differences between the texts, like it is done for the critical editions of the Bible text.
Until Muslim scholarship will become serious and honest about a critical investigation of the old Qur'anic manuscripts, we are mainly left with guessing, apart from a few documented facts some of which are collected here under the title Variant Readings of the Qur'an. But making access to the Qur'an manuscripts difficult is not inspiring much confidence in the claims of textual preservation of the Qur'an.
About textcritical scholarship on Bible and Qur'an (on another site).
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