Questions & Answers about Надень тёплое пальто, не то замёрзнешь.
Could I use а то or иначе instead of не то here?
Yes, absolutely. Не то and а то are both conversational ways to say 'otherwise' or 'or else' when giving a warning about a negative consequence. Иначе means the same thing but sounds slightly more formal or neutral, whereas не то fits perfectly with the casual tone of telling someone to grab a coat.
I always mix up надеть and одеть. Why is it надень here?
The classic rule is: you put clothing on yourself (надеть что-то), but you dress another person (одеть кого-то). Since the speaker is telling the person to put a coat on themselves, the imperative of надеть (надень) is the correct choice here.
Why doesn't пальто change its ending since it's the direct object (accusative case)?
Пальто is a borrowed foreign word. In Russian, nouns of foreign origin ending in -о, -е, -и, or -у are generally indeclinable, meaning they never change their endings no matter the case. The adjective тёплое does take the neuter accusative form, which just happens to look identical to its nominative form.
Why does замёрзнешь mean 'you will freeze' without using the future tense helper word будешь?