Learn Hardcore Romanian: Dumneavoastră ați mers cu metroul ieri?

Dumneavoastră is the formal/respectful singular you in Romanian. It uses the same verb forms as the second-person plural and is used to address someone politely.

Why is the verb written as ați mers rather than just mers?

Romanian forms the compound past tense (perfectul compus) with the auxiliary verb a avea (to have) and the past participle. For second person plural (or formal singular), the auxiliary is ați and the past participle of a merge is mers, so ați mers = you went.

Could I use ai mers instead of ați mers?

Yes. ai mers is the 2nd person singular informal form (with tu). You would then say Tu ai mers cu metroul ieri? But with Dumneavoastră you must use ați mers.

Why is it cu metroul and not pe metrou?

cu expresses the means of transportation (like by).
Romanian typically says a merge cu metroul – to go by metro.
While you might hear pe metrou to mean on the metro, cu metroul is the standard way to say by metro.

Why is the article attached to metrou as metroul?

Romanian uses enclitic definite articles: nouns attach the article to their end. Thus metrou becomes metroul → the metro.

Is it okay to drop Dumneavoastră and just say Ați mers cu metroul ieri??

Yes. Romanian is a pro-drop language: you can omit subject pronouns unless you want emphasis or clarity. The verb ending still indicates person and number.

Why is ieri placed at the end of the sentence?

ieri means yesterday and Romanian adverbs of time are flexible in word order. You can say either:

Ieri ați mers cu metroul?
Ați mers cu metroul ieri?
Both are correct; order depends on emphasis and style.

How do I make this sentence negative?

Insert nu before the auxiliary:
Nu ați mers cu metroul ieri?
That means you didn't go by metro yesterday?

What is the difference between perfectul compus and imperfectul in Romanian?

perfectul compus (ați mers) describes a completed action in the past, often equivalent to English past simple (went).
imperfectul (mergeați) describes ongoing or habitual past actions, e.g. Dumneavoastră mergeați cu metroul = you used to go by metro.