Hittite preterites

From: P&G
Message: 21065
Date: 2003-04-17

Here is a cross-posting from the Indic list.  Someone may have a helpful response to make.
A curious thing about Hittite and the RV injunctive is that in Hittite,
secondary endings are said to function as marking a preterite.
I can't see how the RV injunctive functions develop out of a

Also, according to Bybee et al "The evolution of grammar", zero past
vs marked present is unknown in contemporary languages. This makes
Hittite seem quite strange. There have been suggestions that
sentence particles in Hittite had an aspectual role. I wonder
what the current thinking is.