Breakdown of Sinun täytyy pukea lämmin takki tänään.
tänään
today
täytyä
to have to
lämmin
warm
sinun
your, yours
Questions & Answers about Sinun täytyy pukea lämmin takki tänään.
Why is the object lämmin takki instead of the genitive-accusative lämpimän takin?
This is the special rule for necessity sentences! When the main verb expresses necessity (like täytyy), a total object doesn't take the usual -n ending. Instead, it stays in the basic nominative (dictionary) form, which is why we see lämmin takki.
Why is the word for "you" in the genitive form sinun instead of sinä?
Verbs expressing necessity, like täytyy, require their logical subject to be in the genitive case. You can think of the structure literally as "Of you, it is necessary to put on a warm coat."
Since the subject is "you", why isn't the verb conjugated as täydyt?
Necessity verbs don't conjugate to match the subject. They always stay frozen in the 3rd person singular form (täytyy), regardless of whether I, you, or we have to do the action.
Can I also use pukea if I want to say "You are wearing a warm coat"?
No, pukea specifically refers to the active motion of putting clothes on or getting dressed. To say that someone is currently wearing something, Finnish uses a completely different structure, usually involving the verb olla (to be) and the word päällä (on top).