Pteterito-presentic and active/passive

I've earlier tried to explain the Germanic t-preterite as derived from
a construction with the subject in instrumental and the verb in the
impersonal perfect in *-to (that form in due time became the 3sg
passive perfect), later with the subject in the nominative and
personal endings added to the verb, generalized from the 3sg, which
BTW would explain the absence of ending in the Germanic 3sg
t-preterite. Cf the similar endings in Gothic 3sg passive bairada "he
was carried" and 3sg active t-preterite salboda "he anointed".

The Germanic preterito-presentic verbs, many of which are modal in
sense, have for presence an active perfect and for preterite thus a
passive perfect. Odd. As if the verb was active and passive in sense
at the same time, as eg Engl 'feel' 'I feel it' vs. 'it feels'.
BTW, so is the case with at least one Latin verb: o:di:, o:sus sum "I
hate" (and possibly more?), for presence an active perfect and for
preterite a passive perfect.

In Dutch, the modal verbs can be used also in a passive sense:

Dat kan "That is possible" vs. Hij kan ... "He can ..."
(cf Sp. si puede, It. si puó, further Am.Engl. can do
Dat moet "That is necessary" vs. Hij moet ... "He must ..."
Dat mag "That is permissible" vs. Hij mag ... "He may ..."

which makes me wonder if the Germanic modal verbs originally had only
the passive sense and construed with the subject in the dative, so
To-him, it-is-possible ...
To-him, it-is-necessary ...
To-him, it-is-permissible ...

The sole modern surviving non-modal preterito-presentic verb *woid-
"know" has an adjective *wis- "certain" that fits nicely into this
pattern (escept it's not o-grade)
To-him, it is certain ... "I know"

But still I can't see where the tense distinction comes from. Why did
in the preterito-presentic verbs the perfect active become presence
active and perfect passive become preterite active? Perhaps those
presents were originally similar to the Hittite hi-presents, ie
perfects with added -i, which was later lost?


Torsten