This is what Antonio Loprieno says about Ancient Egyptian negation on page 127 of Ancient Egyptian: A linguistic introduction (1995):
"From an etymological point of view, nn is presumably the result of the addition of an intensifier to the nexal nj, much in the same way in which similar predicate denial operators developed in Indo-European languages: Latin non < *ne-œnum 'not-one,' English not, German nicht < *ne-wicht 'not-something,' etc."From the immediate sound of it, I'd gather that Loprieno's use of "presumably" introduces a theory that the author himself considered possible but unverified. (The direct comparison with Latin non is naturally not to suggest that Egyptian and Indo-European negation are somehow related.) However this comparison still strikes me as awkward, perhaps because the direct comparison of the intensifying -n of Latin non with a merely implied suffix *-n in Egyptian nn is just *too* conveniently similar to me.
I also question that this transliterated nn properly reflects the intentions of the Egyptian scribes to write two instances of actual /n/. The simultaneous use of a negation nj suggests another interpretation to me. I find that in a wide number of languages, a negational morpheme will have both full and reduced variants which may share a common etymology. In French, for example, there is both unbounded non (when answering questions or negating adjectives, for example) and the reduced form ne used before verbs (normally with added pas, plus, guère or jamais after the verb, of course).
So can I get away with imagining something like Middle Egyptian *anī with reduced *ani behind spellings nj and nn respectively? How have others reconstructed this word? In this view, the terminating -n in the latter transliteration would not be actually phonetic but rather the byproduct of the lenient rules of the Egyptian writing system in how speech sounds are expressed. Consider that the Egyptian writing system evolved not just pragmatically as a writing system but also as a kind of sacred art form with much room for artistic creativity. As we see by how negation was often written (see image above), the second glyph (water symbol) may simply be meant to reinforce the /n/ already represented by the double-arms. And when we find, for example, the negational double-arms followed by not one but two water symbols, does this really prove two literal /n/'s? Or is it meant as a clever rebus showing a "dualized" /n/, thereby to be read nj (nb. the dual marker happened to be -j)?
Loprieno does in fact confess back on page 125:
"[...] the second one shows the same logographic sign accompanied by the phonogram n /n/ [...] and is conventionally transliterated nn, although it probably exhibited just a single /n/; [...]"When I think about it more, these choice of glyphs to write negation in hieroglyphs is likely to have come about simply to disambiguate from the word 'of' which was already written as a single n. In actual speech, the difference between words 'of' and 'not' then should depend only on the choice of accompanying vowels surrounding the single /n/.
If so, Loprieno's example of Latin non and the suggestion of an alleged intensifying suffix amounts to a bit of a distraction from a likelier reality, as far as I can piece this together so far.
(2011 June 20) I repaired a teensy error I just noticed in my post, "the masculine dual marker happened to be -j", which I corrected to "the dual marker happened to be -j" since technically the masculine dual in all was properly -wj while it was -tj in the feminine dual.