This might look irrelevant. However:
Mordva has both an indefinite and a definite nominal paradigm.
Example: moda "earth"
case indefinite definite
Nominative moda moda-s´
Gen/Acc moda-n´ moda-n´t´
Dat/All moda-n´en´ moda-n´t´en´
Inessive moda-so moda-son´t´
Elative moda-sto moda-ston´t´
etc
The -n´t´- 's are generalised from *-m-t- (*-m accusative and *-n
genitive and adjective-formant)
from Daniel Abondolo: The Uralic Languages
"
Secondary and tertiary declension.
Metadeclensional forms may be obtained by attaching definiteness
strings such as sN -s´ sGA -n´t´, sDAll -n´t´en´ to most already-
inflected case forms. Thus to the indefinite inessive form of
moda "earth, ground", moda-o, one can add the definite sN ending -
s´, yielding modasos´ "that which is in the ground", the definite
inessive ending -son´t´, yielding modasoson´t´ "in that which is in
the ground", and so on. Each of the eleven definite case strings can
be added to forms inflected for at least six of the cases (genitive,
inessive, elative, translative, abessive, comparative). Such
metaforms are built to genitive bases by the addition of a
reduplicative: sN -s´es´, sG -s´en´t´, sDAll -s´en´t´en´, and so on.
e.g. secondary lative form of the genitive vir´-en´-
s´es´t´en´t´ "out of that of the forest"
Parallel to secondary forms such as the secondary inessive moda-so-
s´ cited above there exist tertiary, essentially synonymous, forms
in which the -s´es´ (-s´en´t´, -s´en´t´en´, etc) endings are added
to an inflected form augmented by -n´-, eg. sN moda-so-n´-s´es´, sG
moda-so-n´-s´en´t´ ...
"
BTW note Nom -s, Obl -t, supposedly from demonstratives. It looks
familiar.
I was wondering whether hypothetical PIE secondary and tertiary
declensions might explain some of the stem extensions of PIE nouns,
eg. are s-stems a secondary declension on the genitive?
Wrt n-stems, PIE has no case ending in *-n, but it does, like PFU,
have a adjective-forming suffix *-n. Now suppose PPIE NP's did not
have full agreement; we might have
<def art> <adj>-n <N>-case-ending
Ø <adj> <N>-case-ending
suddenly, full agreement become fashionable:
<def art>-case-ending <adj>-n-case-ending <N>-case-ending
Ø <adj>-case-ending <N>-case-ending
Voilà: weak and strong inflection (in Germanic).
Torsten