In their book Runic Inscriptions of Viking Age Dublin, Barnes, Hag-
land and Page write the following words of interest pertaining,
among other things, to the differences between East and West Norse:
'The Dublin runic inscriptions, according to the archaeological
datings given to the layers in which the artefacts were found, all
fall within the period c. 950-1125, though there are occasional
uncertainties, as in the case of IR 14. Greenmount, Killaloe and
Beginish, although much harder to date, seem of a similar age. Their
rune forms and language suggest that they were made in or close to
the eleventh century. Roosky appears to be an arm-ring type dating
from the late ninth or early tenth century (Graham-Campbell 1976, 51-
3).
By 900 Scandinavian speech had become established in much of the
Irish Sea area: in Orkney and Shetland (as the sole or dominant
language); in northern Scotland (in combination with Gaelic and
other languages); in the Hebrides (in competitions with Gaelic, but
probably as the dominant language in the more northerly islands); in
Man (probably as the dominant language, but with some competition
from Gaelic, and possibly from Anglo-Saxon and P-Celtic); in a few
parts of Wales (in competition with Welsh); and in the towns of
Ireland, which the Scandinavians appear to have founded - how far
these towns were purely or largely Scandinavian-speaking is unclear,
as is the extent to which Scandinavians settled elsewhere in Ireland.
From archeaological, historical and onomastic sources, we know that
the Scandinavians who settled in the Irish sea came chiefly from
Norway, although a good number of those active in Ireland appear to
have been of Danish extraction, in so far as such national designa-
tions are valid for the Viking Age. Linguistic questions to be asked
in connection with the Irish runic inscriptions are therefore: to
the extent that they are written in Scandinavian, what type of
Scandinavian is it, and how far may the language have been influenc-
ed by Gaelic or any other language?
It is a widespread assumption that Scandinavian during the Viking
Age was a relatively homogeneous form of speech which exhibited only
small dialectical variations. Haugen (1976) terms it 'Common Scand-
inavian', but is nevertheless careful to point out that this is 'a
useful abstraction for the common elements in what were no doubt
both geographically and historically diveging dialects' (p. 150).
'By the end of our period (1050),' he adds, 'we will have to speak
of an East and a West Scandinavian area.'
Traditionally, the speech of Denmark and Sweden is classed as East
and that of Norway and Iceland as West Scandinavian. Characteristics
of East Scandinavian is monothongisation of /au/, /ei/, /öy/ to /ö:/,
/e:/, /ö:/ respectively; the absence in many cases of mutation (esp-
ecially the labial variety); an increased incidence of breaking;
retention of the distinction /r/:/z/; fewer consonantal assimilat-
ions; and an -s (rather than sk) form of the so-called 'middle
voice'. As the Viking Age merges into the Middles Ages, many other
differences become noticeable, e.g. a tendency in East Scandinavian
to move from the word order (head + modifier) to (modifier + head);
and in West Scandinavian to generalize the root þe(ss)- in the pro-
noun meaning 'this', where East Scandinavian retained for this pur-
pose a compound consisting of the basic deictic pronoun sá,sú,þat +
the particle -si or -a. '
The text continues, applying these criteria to show that the Dublin
inscriptions and others are largely West Norse, and in other ways
elaborating on the topic. I wanted to quote the above section, as I
feel that it provides a reasonable summary of basic differences that
developed between East and West Norse without being too technical. I
will try to make a point of pointing out such differences as they
come up in discussions on Norse_Course.