In class we recently covered the nominative possessive pronoun, мой,твой,его, etc. modified by number and gender. When I looked ahead I was surprised to find that these pronouns are further declined by case. Of particular conflict is the genitive case (which I admit we haven't covered yet) whose purpose seems to be indicating possession - Моего, Твоего, etc. What are the use cases for all of these? To say, "I met my cat today", do I use nominative possessives since I am the subject, or genitive possessives because I'm...possessing?
You may be confusing two phenomena here, and the fact that both are described using the term "possession" does not help at all. Let's see.
Мой дом = My house = The house which belongs to me.
The possession here is expressed by the possessive pronoun мой — 1st person, masculine, singular (and, incidentally, Nominative). So far so good.
Мой отец = My father.
Of course my father doesn't belong to me but the grammatical meaning is still the same. :)
Okay. Now let's look at the Genitive where it, according to textbooks, shows possession:
Дом отца = The house of father = father's house.
Отец takes Genitive отца to express the fact that the house belongs to the father. That's what they mean when they talk about that "possession" function of Genitive.
So what happens if it's the house of my father? Well, father should obviously take Genitive as we just saw. But the possessive pronoun мой must agree in case with its object. So мой отец becomes моего отца:
Дом моего отца = the house of my father.
The possessive pronoun мой/моего means that we are talking about my father, i.e. the father who "belongs" to me. The Genitive case of my father has nothing to do with the fact that we are talking about my father but expresses the fact that the house in question belongs to that very old man (who by a totally unrelated twist of circumstances belongs to me).
I hope this relieves the confusion of possessive pronouns in Genitive ("possessive") case. :)
Expressing possession is just one, and I daresay by far not the main, function of Genitive. Briefly, and very generally, cases are part of the government system used by Russian (and almost completely lost by e.g. English) where different verbs and prepositions require their dependent nouns to take specific forms (see also what @Yellow Sky says on prepositions below). You'll certainly learn a lot more about this phenomenon in your class. But for now I'd just discourage you from believing that those simplified explanations of the cases' functions are 100% accurate or indeed exhaustive.
To make life a lot easier, you'll only need to learn how to decline мой, твой, свой, наш and ваш. Его, её and их look the same in all cases, genders and numbers.
Possessive pronouns may be said to describe quality (well, sort of), so the ones which do decline do so very much like adjectives. Just wait till you know how to decline adjectives and you will see how similarly the possessive pronouns decline.
In your I met my cat example the reflexive possessive pronoun свой must replace the normal possessive pronoun because it refers to the subject pronoun я.
Finally, you may find this old post by @CocoPop helpful:
Well, yeah, Russian is a language with cases and also declines pronouns. A sentence like
Я вижу твоего кота - I see your cat
may have you thinking the genitive is used here, when in fact it is just the accusative form, that just happens to have the same form as the genitive (this particular form of the accusative is used with animate objects, like people and animals). So it would be wrong to say that the genitive case is used in this sentence, and you should not confuse the two.
Я вижу твой дом - I see your house.
Я вижу твоего отца - I see your father.
In both cases, the accusative is used for the direct object (
отца), but animate objects just take a different form of the accusative, that happens to look the same as the genitive case.
There are two groups here.
- мой, твой, наш, ваш behave like adjectives, i.e. they modify the noun and take its gender (number) and case
- его, её, их are derived from corresponding Genitive pronouns and do not change in any way. Also, they don't get an initial «н» regardless of the environment.
"У кого-то есть что-то" is one of the easiest example for the use of Genitive, so might as well try that:
- У моего брата есть машина.
- У твоей сестры есть машина.
- У нашего папы есть собака.
Here, мой, твой, наш take Genitive because брат, сестра and папа have to be in Genitive in the first place, and possessives just follow.
Your example would be "Я сегодня увидел свою кошку".
Third person possessives remain the same: У её/его/их брата есть машина, Я увидел ёё кошку etc.
There are several ways Genitive is used in Russian, here are just some of them:
Possession. The name of the possessor must be in Genitive, so if the possessor is "my friend", both "my" and "friend" take Genitive,
мой друг (Nom.) - my friend
дом (Nom.) моего друга (Gen.) - the house of my friend
Direct objects in negative sentences. Very often they are in Genitive.
Я видел твой дом. (Acc.) - I've seen your house.
Я ещё не видел твоего дома. (Gen.) - I haven't seen your house yet.
After some prepositions. Many prepositions like от, из, для, без, etc. need a noun in Genitive after them, if there is a possessive pronoun referring to the noun, it is also in Genitive.
от моего дома - from my home
для моего друга - for my friend