I've been wondering how a word for 'river' (yes, it's *(H-)-bh/p-r/l-
http://www.angelfire.com/rant/tgpedersen/Opr.html
again, sigh) could be related to ad-/pre- (eventually pre- and
postposition) like *(s)up- 'under; on', *(s)up-r- 'over, across' when
I got an idea from a posting by Loreto in Austronesian. It's this: in
stationary societies (let's assume one eg. on both sides of a river)
some locative expressions are not absolute, but relate to prominent
features (eg mountains, rivers) at the place they live (I read
somewhere a long time ago). Take eg. the Nordwestblock, where many
rivers named eg. <X> will have a secondory name <X-apa> (especially
if the name <X> is difficult to inflect if it's a loan from some
older stratum). Now inflect the <-apa> part in various locative and
directional cases, and one has invented a postposition (cf German
postpositions in <fluss-auf> 'up river', <fluss-ab> 'down river'.
Lithuanian has developed new directional cases from an element <-p(i)
>, which is probably the same (T&K).
From there, one might invent preverbs; Møller's example:
<das meer-bi segeln> 'the sea-on sail' >
<das meer besegeln> 'be-sail the sea'
BTW if anyone finds the thinking behind this muddled, rest assured I
do too; maybe one day I can express it clearer.
Torsten