This phrase was taken from the fiction book called "Curious Incident of the Dog in the Night-Time". I'm trying to read the German version of the book ("Supergute Tage oder Die sonderbare Welt des Christopher Boone"). In the chapter 11 there's this first phrase:
"Dann kam die Polizei."
I'm looking for the subject. Is there a subject in this phrase? Would "Die Polizei" be the object? What is the structure here? I'm a very beginner in German.
There is, the subject is die Polizei.
In German, the subject in declarative sentences is often found in the position to the left of the finite verb (pre-field): Die Polizei kam. Sie spricht Deutsch. These are the sentence structures that one would typically encounter in a beginners' class.
However, that is not a necessity (there are studies suggesting this is only true in about 50% of the cases). Many connectors can take this pre-field position as well, the reason typically being that this allows them to more clearly express the relation of the internal ("the statement that follows") to the external connect ("the previous statement"). Take your example sentence: Clearly dann directly refers to a previous statement. There must be some context, presumably some sequence of events (First x happened. Dann kam die Polizei.). On a purely intuitive level, you would perhaps even expect in such a sequence of events that the dann wants to be as close as possible to the preceding event, just to better serve its "structuring" function. And, indeed, dann in this sequencing function is mostly found in the pre-field. (Die Polizei kam dann would be fine in terms of grammar, but for the foregoing reasons, speakers would clearly prefer the other version.)
With dann in the pre-field, you immediately know that die Polizei must move somewhere to the right of the finite verb. There's just no other place to go, you can't squeeze it in between the dann and the finite verb. (This sounds technical but in practice it will become intuitive at some point.)
In the sentence
Dann kam die Polizei.
die Polizei is the subject. You can rearrange the sentence like this:
Die Polizei kam [dann].
It's just the other way because dann refers to something that happened before and is obviously mentioned just before that phrase.
