Specific Satzglieder in a particular sentence

Question

I recently stumbled over this sentence and can't figure out which Satzglieder it consists of:

Ich steige vom Bus in den Zug um.

I realise that Ich is the Subjekt and steige … um is the Prädikat, but I really struggle with the parts vom Bus and in den Zug. Are these adverbiale Bestimmungen or Präpositionalobjekts? Could you ask something like

Wohin steige ich um? → In den Zug.

or would that be grammatically incorrect? Additionally, would it be different when um is omitted in the sentence

Ich steige vom Bus in den Zug.

Without um it seems to me that there's more freedom as to which prepositions you can use. Maybe I'm just overthinking this, but to me, nothing really seems to make sense and before I spend the entire day trying to figure this out, I decided to ask here, hoping that someone smart(er than me) could help me on this. Feel free to provide other example sentences etc.

Answer 1

Both vom Bus and in den Zug in your examples are adverbials.

Prepositional objects differ from adverbials in that their preposition cannot be understood in the usual sense. For example, in

Ich warte auf den Bus.

you can't read that auf den Bus as a direction. It makes no sense. So it must be a prepositional object and that must be a phrasal verb warten auf+‹Akk›. Compare:

Ich warte auf dem Platz.

This is indeed an adverbial and it specifies the location where you are waiting. At the square. The verb phrase is a plain warten. You could even say

Ich warte auf dem Platz auf den Bus.

with the phrasal verb warten auf+‹Akk› and an additional adverbial that tells where you are waiting.

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Additionally, would it be different im the sentence were "Ich steige vom Bus in den Zug.", omitting the "um". Without the "um" it seems to me that there's more freedom as to which prepositions you can use.

You can use both steigen or umsteigen in that example, and vom Bus and in den Zug are still adverbials. As both steigen and umsteigen don't feature a prepositional object.

But be aware that the meaning is slightly different. Steigen is more near to the actual movement, while umsteigen means that you change your means of transport.

So if you say steigen instead of umsteigen, people assume that you move directly from the bus to the train without touching the ground.