Learn Hardcore Polish: Musimy wyjść z mieszkania wcześniej, żeby szef mógł wejść sam. - We must leave the apartment earlier so that the boss can enter by himself.

Polish verbs come in aspect pairs: wyjść is perfective (completed action), wychodzić is imperfective (ongoing/repeated action). With musieć you choose perfective when you mean “we have to actually leave (and finish that action),” so musimy wyjść is correct. Saying musimy wychodzić would sound odd, as if you repeatedly have to be in the process of leaving.

Why is z mieszkania in the genitive case?

The preposition z (“from”) always requires the genitive case when indicating origin or separation. Mieszkanie (nominative) becomes mieszkania (genitive singular), so z mieszkania means “from the apartment.”

What does żeby mean here, and could we use aby instead?

Both żeby and aby introduce purpose clauses meaning “so that” or “in order that.” Żeby is more common in spoken or neutral styles; aby is slightly more formal or literary. You could say aby szef mógł wejść sam, but in everyday speech żeby sounds more natural.

Why is szef mógł wejść using mógł instead of może?

When you introduce a subordinate clause with żeby or aby, Polish uses a so-called conjunctive mood, which in modern Polish looks like the past form of the verb. So instead of the present może (“he can”), you use the past form mógł to express “might/could” in this purpose clause.

What role does sam play in szef mógł wejść sam?

Here sam means “alone/by himself.” It emphasizes that the boss should enter without any of you accompanying him. It agrees in gender/number with szef (masculine singular).

Can the żeby-clause come before the main clause?

Yes. You could say:
Żeby szef mógł wejść sam, musimy wyjść z mieszkania wcześniej.
This inversion is grammatically fine, though in Polish it’s more typical to state the main clause first.

Why is the infinitive wejść placed at the end of the subordinate clause?

In Polish a modal or semi-auxiliary verb like mógł is conjugated, and the main action verb stays in the infinitive. Word order is flexible, but the pattern conjunction – subject – modal – infinitive – adverb is very common. Moving wejść elsewhere would sound unusual.

Could I replace wejść sam with wejść samemu or samemu wejść?

No. Wejść is an intransitive verb and sam as an adverb/adjective stays in its base form, agreeing with the subject in gender/number. Samemu would be the dative or instrumental form of sam, which doesn’t fit here. The normal form for “alone” after an intransitive verb is sam (or sama/sami/same to match the subject).