Breakdown of Ona musi być chora, skoro śpi całe popołudnie.
być
to be
ona
she / it (f)
spać
to sleep
musieć
to have to
Questions & Answers about Ona musi być chora, skoro śpi całe popołudnie.
Why is there no preposition before całe popołudnie? Don't we usually need przez to say 'for' or 'through' an amount of time?
You can use przez (as in przez całe popołudnie), but in Polish, continuous duration is very often expressed using just the bare Accusative case. This is especially common with time expressions involving cały (the whole) to emphasize an uninterrupted stretch of time.
What is the nuance of using skoro instead of bo or ponieważ here?
Skoro translates best to "since," "seeing that," or "given that." It is used when drawing a logical conclusion from an observed fact. While bo and ponieważ simply mean "because" and state a direct cause, skoro highlights your deduction process (Fact: she is sleeping all afternoon; Deduction: she must be sick).
Why is chora in the Nominative case? Doesn't the verb być require the Instrumental case?
This is a common trap! The verb być requires the Instrumental case when it is followed by a noun or a noun phrase (for example, Ona musi być dobrą pacjentką — She must be a good patient). However, when być is followed only by an adjective, the adjective remains in the Nominative case, which is why we use chora.
Can musieć (must) be used to make deductions in Polish, just like in English?