There are constructions in Dairwueh and Bryatesle where adpositions mark subjects. This is especially common in subordinate clauses, but not entirely unusual in main clauses either. Let us start out with the ones that work in both sub- and main clauses.
This essay has probably sat in the drafts folder for eight years by now so I figure it's time to publish it even though it's a bit rough.
1. The Dairwueh preposition 'teu'.
'Teu' has several uses, but the meanings nearly all derive from 'kind of'. A kind of, the kind of, some kind of, this kind of. It is very common when making categorical statements: teu darat tsem [...]
Its nature as a preposition is clear from the following facts:
- its complement is in the locative-instrumental
- it can be coordinated with certain other prepositions
- it can take a preprepositional.
- The preprepositional argument marks the use for which the kind(s) are meant - e.g. kaubeng teu dorule = health kind-of food ~ types of food intended for health
- It also marks a supercategory of which the thing is in a category "salar teu balin" - animal kind-of horse 'an animal, specifically a kind of horse'
2. Dairwueh burn and melt/dissolve
Not even in modern times does Dairwueh normally distinguish 'dissolve' from 'melt'. However, in chemistry and other contexts where the difference has some significance, the subject of 'dissolve' is often marked by the preposition yil (sometimes lo or əre), whereas melt tends to be reflexive. Similarly, chemists tend to distinguish two types of burning by marking the subject with a preposition.
A fire with visible flames has a normal subject, chemical corrosion uses yil or lo.
3. Bryatesle 'few'/'little'
In Bryatesle, 'few' operates syntactically as a postposition. It normally takes the accusative case, with the ablative used when expressing the sense of 'too few'. They are also found in coordinations with the following postpositions or in similar positions
- with, without (as in 'in association with')
- full of
- instrumental adpositions
It cannot stand as the subject of a transitive verb, but can be the subject of an antipassive construction.
4. The Bryatesle 'associative preposition'
Although Bryatesle primarily has postpositions, the grammaticalization path that lead to the associative preposition caused it to end up on the other side. The associative preposition simply is a marker of metonymy. Not necessarily mandatory whenever metonymy is involved, but quite often used for that purpose.
5. Sometimes in comparisons
In both Bryatesle and Dairwueh, it happens that both the comparanda are marked by the comparative marker.
6. Presence of vocatives
The presence of a vocative in a clause can cause the subject to be marked by adpositions in both Bryatesle; primarily the postposition '(+abl) gyner'.
7. In some subordinated coordinated structures where subjecthood is unclear
8. Resumptive pronouns
Resumptive pronouns in relative subclauses almost always have the postposition 'gyner' in Bryatesle.
9. In subclauses specifying the place or time of something.
10. The Dairwueh preposition 'ne'.
This preposition can be used with subjects and objects, but has several functions, and is not triggered by things "outside of" the NP, unlike the previous examples.
So, in what way are these subjects and not adverbs that just are topicalized?
The main reason would be their syntactical effects. I will list the very subject-like ones first:
- Permit reflexive reference
- Cannot be coordinated with adverbs
- Can be coordinated over gaps with subjects
- Have subject-like scope
- Undergo raising like subjects do
However, things that may look non-subject like include
- They block congruence on verbs
- The presence of an adpositional subject requires an adposition also in the complement of the copula in Bryatesle
- The preposition blocks the use of genitive for definite subjects in Dairwueh, and the neuter-ergative is blocked in Bryatesle.
- Explicitly transitive verb forms are nearly never permitted
- The Bryatesle 'few', for instance, requires a detransitivized verb whenever the English corresponding sentence would have 'a few ...' be the subject of a transitive verb.