Breakdown of Byliśmy na plaży i nagle zwiało mu kapelusz.
być
to be
i
and
on
he / it (m)
na
on, at / to (motion toward) / for (a meal) / for (waiting for)
Questions & Answers about Byliśmy na plaży i nagle zwiało mu kapelusz.
Why does this sentence use the neuter verb zwiało instead of a masculine verb like wiatr zwiał?
This is the impersonal neuter past, used to describe uncontrollable events, accidents, or natural forces. Polish often drops the specific subject (like the wind) and uses a 3rd-person singular neuter verb to express that "it just happened." You could say wiatr zwiał, but zwiało emphasizes the sudden, uncontrollable nature of the event.
Why do we use the dative pronoun mu here instead of the possessive jego (jego kapelusz)?
When an action happens to someone's clothing, body parts, or personal belongings, Polish strongly prefers using a Dative pronoun to show who was affected by the action (the "experiencer"). Saying zwiało mu kapelusz (literally "it blew the hat to him") sounds much more natural to a Polish ear than using a possessive word like jego.
What is the infinitive of zwiało and does it have any other meanings?
The infinitive is zwiać, which is a perfective verb meaning "to blow off" or "to blow away." As a B2 learner, you might also recognize zwiać as a very common colloquial word for "to run away" or "to flee" (e.g., Musimy stąd zwiać! - We have to flee from here!).
Is kapelusz the subject of the second clause?