Originally Posted by
Shady_arc This is called "government": certain prepositions or contructions require a specific case.
C(со) + GEN is used for the meaning "down (from)".
За requires Instrumental in several meanings; most important of those are "behind"(place, rather then motion to get behind smth) and "to get something": "Магазин был за остановкой", "Я сходил за булочками".
Я видел как../Я слышал как../Я чувствовал как... is a standard consturction to express the idea of seeing/hearing and so on different thing as they happen. Like in English sentences "I saw him painting the wall", "I heard her being shot", "I felt rain drops running down my forehead". One of the things that are as easy in Russian as they are in English. Whatever the event was, just use "как" + sentence with no changes (). For example "rains drops run down my forehead" --> "rain drops were running down my forehead" --> "капли дождя стекали по моему лбу"--> "Я чувствовал, как капли дождя стекали по моему лбу" **
** if a sentence describes a process "rain drops were running down my forehead" in imperfective, you may as well use present tense after "как": "Я чувствовал, как по моему лбу стекают капли дождя".
"Конец холодам": "холода" means "cold weather" in general. "Конец холодно" is ungrammatical. Would be something like "The end to the is cold". "Холодно" is a short-form adjective, so it makes zero sense to use it as a NOUN in an oblique case (short-form adjectives are only ever used in a nominal predicate,i.e. as the verb in the sentence).
"свой" is a reflexive pronoun "oneselve's", which means my/his/her/John's/cat's and so on, depending on who or what is the subject of the sentence you use it in. Or a clause. Yes, I mean in a sentence like "I said that he must call his mother" use of "свой" in place of "his" will clearly refer to "his mother" rather than "my mother". "I" am the subject of the main sentence, but in the clause "he must call his mother" - it is "he" who is the subject.
This reflexive pronoun declines like an adjective, which is hardly a surprise. Because is is used just as an adjective: to describe nouns. Note that "себя" (oneself) clearly cannot have a Nominative (because it only refers to a subject of the sentence, which already is in Nominative somewhere else). Свой works as an "adjective", so it does have Nominative свой/своя/своё/свои depending on the gender and number of a word it refers to.
You don't have such a pronoun in English, so in complex sentences pay close attention, if there is such subject at all. In my example above, "Я чувствовал, как капли дождя стекают по моему лбу", you cannot use "свой". The clause "Rains drops were running down my forehead" has "rain drops" as a subject, and these clearly got no forehead. So "капли дождя стекают по своему лбу" is nonsense.