Semantic differentiation between thematic and athematic?

From: Andrew Jarrette
Message: 38149
Date: 2005-05-29

I have read that in primitive IE, the verbs with "characterized presents", i.e. with n-infix, nu-affix, zero grade + -j-, sk-affix, etc. are formations built to verbs that are inherently punctual in meaning, and the durative character of the present tense was a secondary notion in these verbs, and therefore was denoted by derived means such as the affixes and infixes mentioned above, in contrast to the uncharacterized (unelaborated) aorist forms of these verbs, which were similar in form to the present forms of verbs that were inherently punctual.  Thus it seems that certain verb formations had an originally semantic function in IE.
My question is, has anyone found a semantic function for the existence in IE of both thematic and athematic verbs?  Why should there be two different types of verb conjugations?  In many cases originally athematic verbs were converted to the more prevalent thematic types in the descendant languages of IE, so there seems to be no practical need for the two types of conjugation.  But perhaps there was an original semantic differentiation between thematic and athematic verbs.  Has anyone found one, and what was it?  Also was there a semantic function for reduplication in the presents of verbs of the reduplicating class (which, apart from reduplication, are conjugated like the athematic types)?  As well, are there specific meanings for each of the various affixes and infixes of the characterized present stems (those that were inherently non-present or non-durative in basic meaning)?
I would most appreciate any response to these questions.
 
Andrew Jarrette