Thank you very much for your answer LN, it is very detailed and
interesting. May I ask if you know of a good reference book on the
subject ? I got myself the three volumes of the "New Introduction to
Old Norse", which have been and still are very helpful to me, but I
start to feel the need for something more than an introduction -
especially since I find easier to develop a sense for Old Norse and
memorize the patterns by understanding how the sounds evolved and
altered each other.

By the way, I noticed in your reply that the icelandic letters weren't
displayed correctly in my (quoted) question: was it the case in my
initial text ?

Thank you !

Gaël

2008/12/13 llama_nom <600cell@...>:

>
> Good questions, Gael. No need to apologise! These masculine nouns with
> u-mutation originally had an unstressed /u/ in some of their endings,
> including the nominative and accusative singular (and the accusative
> and dative plural). This /u/ is sometimes called the stem vowel or the
> thematic vowel. By "originally" I mean in an earlier stage of the
> language, before the Viking Age.
>
> *skelduz > *skealduz > ON skjöldr "shield"
> *arnuz > ON örn "eagle"
>
> (That asterisk * indicates hypothetical reconstructions.)
>
> The /u/ in this class of nouns was inherited from Proto-Germanic and
> can still be seen in Gothic (Go. skildus, ON skjöldr), and in Old
> English where the root syllable is short (Go. magus, OE magu, ON mögr
> "son, boy"). It isn't related to the epenthetic /u/ of Modern
> Icelandic which was a much later development that affected all noun
> kinds of nouns that ended in a consonant followed by /r/. The
> epenthetic /u/ didn't cause u-mutation.
>
> These masculine "u-stem" nouns, as they're called, are masculine in
> related old Germanic languages, and probably also in Proto-Norse and
> Proto-Germanic. There are a very small number of feminine u-stem nouns
> in Gothic and Old English, e.g. Go. handus, OE hand "hand". Probably
> ON hönd "hand" once followed the u-stem declension, but the only trace
> of this left is the dative singular: hendi.
>
> The u-stems are relatively few compared to those masculine nouns that
> originally had other vowels in those endings. That's why most
> masculine nouns don't have u-mutation. Of masculine nouns ending in -r
> in Old Norse, the most common type had /a/ in the nominative and
> accusative singular endings in Proto-Germanic and Proto-Norse.
>
> *dagaz > ON dagr (Go. dags, OE dæg).
>
> Others had /i/ for their stem vowel, which sometimes results in
> i-mutation in the Old Norse word. But often unmutated forms appear,
> especially where the root is short:
>
> *balgiz > ON belgr "skin; skin bag; bellows" (Go. balgs, OE belig).
> *stadiz > ON staðr "place" (Go. staþs, OE stede).
>
> ...and a few more classes too, each with their own peculiarities;
> likewise for neuters and feminines. Hope that helps. Let me know if I
> lapsed into jargon or if there's anything else you're unclear about.
>
> LN