Rob A. wrote:
I also think it brings clarity to the process to try to think of passive and imperative sentences as simply not having a subject...and NOT NEEDING ONE....one of the ways that Finnish grammar differs from "Latinate" and Germanic languages....

One man's clarity is another man's murk.
If you think of the simple imperative
Tule!, I experience the subject as
you. One can even say
Tule, sinä!
I also treat the simple (2p sing) imperative as the truest "basic" form of a verb and almost certainly the first kinds of verbs that existed.
If we look at
mainitse/mainita (mention), the simple imperative is
mainitse, which is also the invariant stem for the present personal endings
mainitse/n etc. (besides 3rd) and also the negative form as in
älä mainitse sitä. And that one relationship is true of
all verbs for which those forms exist at all, which is to say practically all verbs. As much as those forms hop around in behavior over different inflection types, that's a pretty remarkable fact, I think -- but understandable if you take as a given that the real core of the verb is
mainitse.
If we put
mainitse/mainita (mention) into passive imperative,
mainittakoon, että, "Let it be mentioned that", (one of the more common passive imperative idioms) then I also agree that in Finnish, there is no subject.
But in present and past, I see three main types of passive. Let's dispose of the colloquial
Mennään, "let's go," because it isn't really meant literally. It's not uncommon to state the me, though.
Then there is
Senaatissa huhutaan, että hallitus kaatuu, It's rumored in the Senate that the government will fall. Clearly there's no subject there.
But
Hänen oletetaan kuolleen seems different to me. Of course one can arbitrarily make the rule however one wishes, the way X^0 is defined to be 1 (even though it is a common-sensically meaningless quantity) because it's convenient for the arithmetic of exponents.
"He" is the object of the assumption but the subject of the dying and occupies the subject's traditional place in the sentence. I guess I have to go along with you to uphold the arithmetic of exponents because of sentences like
Hänet tapettiin. Now just so I have this straight (fat chance) -- in "He was killed," 'he' is the grammatical subject. But in
Hänet tapettiin, 'hän' is the grammatical object. Is that how the rules work?
If I seem dense sometimes, it's because I am sometimes.