Rob A. wrote:Very nicely explained, Alden....and as you say language learners eventually get to the point were they have enough knowledge that the learning process becomes imitative.... they no longer care about the "why" and are more interesteded in the "what"... I'm almost getting there myself ...

Though I still have this fascination with the "why"...
Kotona....and there are others which, of course, don't come to mind at the moment.....is one of those words which for some reason ...and I'm sure the linguists argue over it, has developed an etrenched usage pattern.....
There is indeed "why" for this phenomenon: in Proto-Uralic the only locative case ('in/at') had an ending
*-na, and the only separative case ('from') had an ending
*-ta. Here the mark * stands for a reconstructed form, although both these endings have preserved in Finnish:
1. In few old words and postpositions they still have local meaning:
koto-na 'at home',
koto-a 'from home' (in the weak grade t has disappeared);
luo-na 'near/at',
luo-ta 'from near/at(?)'.
2. In most words these old cases have developed into more abstract cases: essive
-na ('being as something') and partitive
-(t)a (marking mainly partial object):
maa-na 'as a land',
maa-ta '(at) some land' [as an object, like
näen maata 'I see some land'].
In Mordvin we can still see this kind of abstractization development in progress, and probably it happened in Proto-Finnic (ancestral form of Finnish, Karelian, Lude, Vepsian, Ingrian, Votian, Estonian and Livonian) somehow like:
otin vet-tä 'I took from water' --> 'I took some water'.
Here is an introduction to Proto-Uralic in Finnish, but I'm slowly translating it in English:
http://www.mv.helsinki.fi/home/jphakkin/Kantaurali.xps or
http://www.mv.helsinki.fi/home/jphakkin/Kantaurali.pdf
There is usually a big mental gap between the fennists (studying Finnish) and fenno-ugrists (studying Finnish [and related languages] as a Uralic language) - we the latter are still very interested in "why's" of different phenomena.
