Akk oder Dative (please answer)

[amirhossein]

Hello,

which indefinite articles is true according Akk and Dative grammar?

Sie kommen unter ( ⚪️eine oder ⚪️einer) Brücke durch.
'
'
In answer book have been wrote "einer Brücke" but:
I taught that with preposition "unter" comes "Dativ," if the verb indicates as static state.
While, "Akussativ" is used with the same preposition if the verb indicates as state of motion.
In the question above, "durchkommen" indicates motion, so I thought the article comes in "Akussativ"(eine). Or is it an exception with movements under bridges?

Thank you in advanced

[h34]

You are right, normally 'unter' is combined with the dative to express a static location. With 'unter […] hindurch' this is different. The dative case is used despite the fact that there is a movement. So this is an exception to the general pattern.

Static:
=> unter der Brücke (dative)
Dynamic:
=> unter die Brücke (accusative)
=> but: unter der Brücke hindurch (dative)

By contrast, 'über die Brücke hinüber' is used with the accusative, as you would expect.

I've tried to find a logical explanation but without success. 'Unter hindurch' simply seems to be an exception. There is a discussion about the same topic on Stackexchange but even there nobody seems to have a very convincing answer …

https://german.stackexchange.com/questions/20836/warum-unter-der-br%c3%bccke-hindurchgehen

[h34]

This list of circumposititions could be helpful:
https://files.ifi.uzh.ch/cl/volk/LexMorphVorl/Lexikon07.Prep.html#Zirk

an DAT entlang, vorüber Lokal
an DAT heran, vorbei Lokal
auf AKK hinauf, herauf Lokal
aus DAT her, heraus, hinaus Lokal
hinter DAT her, hervor Lokal
in AKK hinein, herein, hinauf, herauf Lokal
über AKK hinaus Lokal
um AKK herum Lokal
um GEN willen Kausal
unter DAT hindurch Lokal
von DAT aus Kausal
von DAT weg Lokal
von DAT ab Temporal, Modal
vom DAT an Temporal
zu DAT hin, hinüber Lokal

[amirhossein]

Thank you very much "h34" for your complete response.

[kevin]

Maybe it's helpful to think of a case where both are possible, with different meanings.

Wir waren erst noch auf der anderen Straßenseite, dann gingen wir an den großen Baum hinüber.
The tree is where the movement ends, it's the destination, so accusative.

Wir waren erst noch auf der anderen Straßenseite, dann gingen wir am großen Baum hinüber.
Probably we kept walking, but the tree just was the place (static) where we crossed the street. There is a movement in this sentence, but "am Baum" describes a position, not a movement, so dative.

In your sentence, my theory is that "unter der Brücke" describes the space (a position) that is crossed, but this space is not the destination of the movement, it just happens to occur in the same sentence.

[Quetzalcoatl]

I just read the title and I would have spontaneously chosen the dative case, just due to my "Sprachgefühl" without thinking about grammar. (I am a native speaker)

[amirhossein]

Thank you dear "kevin" and "Quetzalcoatl"