I was somewhat gobsmacked (can you be “somewhat gobsmacked”, or is that akin to saying “almost a virgin”?) to read the following comment made by Layton in talking about how he chose his examples:
There is no reason to doubt that Biblical Sahidic Coptic is normal, idiomatic, and polished in character even thought its wording and rhetoric are also governed by the Greek original. (xii)
This brought me to a stop in my reading. As Layton says (albeit much less colloquially) in his opening chapter, there is much about how Coptic operated that we don’t know because it hasn’t been a spoken daily language for around a millennium. He also says that the Nag Hammadi texts “whose language resembles Sahidic display a non-Standard mix of isoglosses, sometimes fluctuating, from all over Egypt” (xii) so he has omitted them. I have no difficulty with the idea that the Biblical Sahidic in the oldest manuscripts is polished. I am less sure that it is necessarily either normal or idiomatic.
I think it is eminently sensible of him to chose the Sahidic Bible and the writings of Apa Shenoute (which he also uses) as the standard for Standard Sahidic because the corpora that we have available are those, Nag Hammadi and non-literary material such as personal, magical, legal and medical texts. I think it making too sweeping an assumption to say that religious texts, especially those translated from another language are either normal or idiomatic, though. Certainly, most modern English bible translations are neither particularly normal nor particularly idiomatic and there are loud cries of dismay when a version comes out that attempts more normal and idiomatic usage (and no, I don’t think I’m confusing this with colloquial usage, which is definitely not well accepted – I am thinking about how well the TEV/Good News is accepted in most church circles).
While we have no evidence that the Copts were like us in this, we have no evidence that they weren’t either. I think it would be safer to assume that the Sahidic Coptic Bible and the writings of Apa Shenoute are good examples of polished, formal, religous Sahidic and since it’s what we’ve got to work with, to use it as the standard. Even in my limited reading of the Nag Hammadi Sahidic corpus, I have come across examples where a word is clearly using the spelling of another dialect, so I would not doubt his expert judgement about the isoglosses in it. I just don’t think we can assume that religious documents are necessarily good examples of normal idiomatic usage and I think that there have been times when too-broad assumptions that “everybody knows” have blinded people to important discoveries for too long in the past.