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Свою (his accusative?)

Его (his) - его + something = his something?

Нем (him) - я думаю о нем ? (prepositional him?)

Него (genitive) - у него ....

Ему (dative) - ему один лет (it's the only use I saw)

1- What kind of his is Его? Why do we have to use свою while saying "Он любит свою маму" because свою is accusative "his"? If it is what is его then?

2- Can't we say он двадцать лет, instead of ему? Would it sound weird?

note (i'm studying with duolingo, it doesn't exactly give any thorough explanation)

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1. Свой is generally translated as "own" i.e. «Я люблю свою кошку» - "I love my own cat". It almost always refers to the subject of the clause owning the modified object.

It is required for third person when the subject owns the object in the clause. (Don't use её, его, or их if the subject owns the object) and is interchangeable in first and second person with мой, ваш, and наш. It is preffered with Ты instead of твой but use of твой is not wrong.

Be careful in multi-clause sentences because it always refers to the subject of the clause it is in, not any other clause. i.e. «Она забыла, где её кошка» calls for её not своя in the second clause.

It declines the same as мой. i.e своего is the genitive. See the declension table under the wiktionary entry.

  1. No you cannot say он двадцать лет. Russian doesn't state age in this manner. Correct form: ему двадцать лет.
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That's a lot of things packed into one.

  1. You can also say я люблю свою маму, or ты любишь свою маму. Свой is the universal reflexive. It means "the sentence subject's own". Он любит его маму would mean "he (e.g. John) loves his (e.g. Pete's) mom".

  2. он двадцать лет would be an unfinished statement: "for twenty years, he..." You can't say "he's twenty" this way for the same reason you can't say "him is twenty" in English.

Oh and by the way, ему один год.

Both его and него can be genitive as well as accusative. The н- has nothing to do with case; it appears after a preposition. The reason is similar to how "an eke name" turned into "a nickname", or "mine Ed" => "my Ned".

The Proto-Slavic prepositions *kъn "to" and *sъn "with" became *kъ and *sъ, but kept their old forms before third-person pronouns; this led to things like *kъn jemu "to him" and *sъn jimъ "with him" being reinterpreted as *kъ njemu and *sъ njimъ, and then, much like with "Ned" and "Nelly", it was generalised to every occurrence of those pronoun forms after a preposition, even the ones that didn't have that disappearing N.

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  • Last 2 passages are a little bit confusing, but I get the idea of Свой now.Does this also apply for Своего or is it just for "her","his"?
    – Burak
    Sep 18 '17 at 16:50
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Let us consider the sentence: "John is washing his car." Whose car is it? John's? Another man? We do not know. Of course, we may say "his own car" to emphasize whose car is it, but in Russian this is not needed. If it is his own car we say: "Джон моет свою машину.", if it is another man's car we say: "Джон моет его машину". Both "его" and "свою" are translated as "his".

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