Finnish declension

"Why is the nominative-like form called an accusative as well?"

I know I'm walking on thin ice, but the thinking may depend on the fact that in case of personal pronouns (the only true accusative forms that everyone seems to agree on) the accusative is used as equivalent to both nominative and genitive accusatives. At a slave market one might say ostan orjan/ osta orja but if one uses hän instead of orja, it becomes ostan hänet/ osta hänet. The grammatical case must be the same both if the object is a noun or if it is a pronoun - ergo, there's a nominative accusative form. In the end, the existence of nominative-accusative is at least partially a question of convention, but this is anyway the convention that is widely agreed upon.

Ok, that is an argument that does make some sense to me at least. The fact that the nominative of a noun becomes the accusative of a pronoun shows that there is a functional connection between the two.

But then, if we include them both under "accusative" then people may think that they're equivalent and interchangeable. We do the same with alternative genitive and partitive plural forms, after all. So I propose changing the table a bit, so that the "accusative" line becomes two rows high, and have two sub-rows each showing the two possible types of accusative. What should we call those sub-rows? Is the imperative the only case where the second accusative (the one like the nominative) is used, or are there others?

Yes, nominative-accusative is used with total objective (partial objective is always in partitive) in all positive passive forms:

ostetaan auto

on ostettu auto

ostettiin auto

oli ostettu auto

ostettaisiin auto

olisi ostettu auto

ostettakoon auto

olkoon ostettu auto

ostettaneen auto

lienee auto

In addition 3rd infinitive instructive both in active and passive, agent participle and negative participle require nominative accusative. Imperative takes genitive accusative in third person.

This is really too long to explain in the template. I think they should be called "nominative-accusative" and "genitive-accusative" which are direct translations of the Finnish grammatical terms nominatiiviakkusatiivi and genetiiviakkusatiivi. The accusative used to occupy two rows before, so that is no problem. Actually, the accusative box could be three rows high:

first row: text accusative on left column, 2nd and 3rd empty

2nd row: text nom. aligned to the right on left column, {{{nom_sg}}} | {{{nom_pl}}} on 2nd|3rd

3rd row: text gen. aligned to the right on left column, {{{gen_sg}}} on 2nd, 3rd empty

How's that?

It should read lienee ostettu auto' above instead of lienee auto.

Is that really an object? As far as I know, the whole idea of a passive is to make the "undergoer" the subject. Like in English they were welcomed.

Finnish does not have passive in exactly tha same sense as in English. Quote from Wikipedia article Finnish language: "The passive voice (sometimes called impersonal or indefinite) resembles a "fourth person" similar to, e.g., English "people say/do/". Your example "They were welcomed" is "Heidät toivotettiin tervetulleeksi", i.e. it really has an object, grammatically speaking.

Which form of the pronouns is used with the passive? Is it the nominative or the t-form?

It's the t-form.

Ok, then I think it would count as an accusative.

I found a scientific paper that uses the same argument. It calls it the "pronoun test": a form is really an accusative, if it turns into the t-accusative when you replace a word with a pronoun.