Parts of speech in the question "Чей это ...?"

Question

When someone asks a question along the lines:

Чей это кот? Чья это собака? Чьё это письмо? Чьи это очки?

I have the following two questions regarding the structure of these interrogative sentences:

1. What type of pronoun is чья/чей/чьё/чьи here? Is it a pronoun which replaces a noun, or a pronoun that replaces an adjective?

For example - "This is your car" -- here "your" takes the place of an adjective

BUT

"This car is yours" -- here "yours" takes the place of noun

So in these questions, does чьё/чья/чей/чьи mean "whose" in the sense of "Whose is this?" (replacing a noun) or "Whose car is this?" (replacing an adjective)?

2. I have an essentially analogous question about the function of "это" in this type of question.

In these questions, does "это" mean "this" in the sense of "Think about this" (takes the place of a noun) or "this" in the sense of "Think about this question" (takes the place of an adjective)?

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My confusion is as follows: чей/чья/чьи/чьё declines with the noun in "...", but this isn't enough to tell us whether it is taking the role of a noun or adjective, because both of these types of pronouns decline the same in Russian -- i.e. "(Это) авто -- твоё." and "Это -- твоё авто." are both valid sentences, and "твоя" is declined the same way in both, despite the fact that it serves a different function in both.

But in German, one would have "Das Auto ist deins" and "Das ist dein Auto". In German one can tell from the declension of "dein" what function it is serving in each sentence, and from that infer what the function of "das" is (along with whether it is separated from the noun by the copular verb, which generally isn't used in Russian).

The only hint in Russian that allows one to differentiate between "Это авто твоё" and "Это твоё авто" (at least as far as I can tell) is the word order. But the rules for word order in questions are usually different from the rules for word order in regular sentences, so I really don't know what at all to make of "Чьё это авто". Hence any help would be greatly appreciated.

Answer 1

Russian is much easier than English or German in this aspect. We don't distinguish between posessive pronouns and adjectives (they are both called pronouns in modern English grammar btw). Neither have we different forms for them like my and mine. It will be мой,моя,мое in all cases,you will never make a mistake. As for Russian into English translating the rule is the same as in English. Just look whether you have a corresponding noun after the posessive in your sentence or not.

Это моя книга.--This is my book. Чья это книга?-- Моя.Whose book is this?--It's. mine.

Answer 2

not sure i fully understand the crux but i'll try to give an answer and hopefully it'll help to arrive at a conclusion

1. in the presented questions the interrogative pronouns point at a possessor of the object in question who (the possessor) is expressed with a possessive pronoun or a noun in Genitive case in the answer

Q.

Чей это кот?

A1 (possessive pronoun)

Это наш кот

A2 (noun in Genitive)

Это кот соседа

there's an obsolete form, yet still understandable, where a possessive adjective is used instead of a noun

Это соседов кот

a modern variant with a regular adjective would be

Это соседский кот

although it's less specific than the former because it doesn't point at possessor's gender and number

that said, a female form of a possessive adjective is still very much in use

Это соседкин кот

BUT correspond the grammatical form of this interrogative pronoun must with the object and not with the possessor
it's essentially a possessive pronoun itself and these always correspond with the object

2. Это here is an demonstrative pronoun, which technically could be replaced by pronouns declined in accordance with the object of the question

Чей это кот? = Чей этот кот?

Чьи это очки? = Чьи эти очки?

though it sounds somewhat artificial and is rarely used

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But the rules for word order in questions are usually different from the rules for word order in regular sentences, so I really don't know what at all to make of "Чьё это авто".

in order to arrive at a function of noun (by your terminology) for это in the answer, a question must be worded in a specific way

Q. Этот кот, (он) чей? A. Этот кот - наш / Он - наш but a regular answer Это наш кот is equally valid

however in a reversed situation an answer Он - наш to a question Чей это кот? sounds awkward, because a purpose of such type of question isn't to find out whom out of several potential owners the cat belongs to, but just to find out in general who the owner is