на день рождения vs на дне рождения

Question

Beginner here. There are 2 similiar sentences talking about a birthday, but use a different case and I am confused why.

The first is Вчера я была у Тамары на дне рождения.

Translation: Yesterday, I was at Tamara's for her birthday.

And the second is Кого ты пригласил на день рождения?

Translation: Whom did you invite for your birthday.

From what I can gather, the first declinates like

дне - locative/prepositional рождения - genitive (day of birth?)

день - accusative (guessing its not nominative) рождения - genitive (day of birth?)

So the first question, is the above correct?

The second question is why the difference? My guess from looking at wiktionary would be accusative is used to say something was for a particular date (more focus on purpose) and locative is used to say something was on a particular date.

Is that correct? Could you give a few other examples?

Would it still be correct to say Кого ты пригласил на дне рождения? like whom did you invite on your birthday? If so, how would the connotation of the question change?

Many thanks

Answer 1

Yes, you've parsed it correctly.

The Prepositional/Locative case describes a stationary condition while the Accusative describes movement/directionality.

The difference is of the same kind as in German if you happen to know it.

Positional: Das Buch liegt auf dem Tisch. (The book is on the table.) - Книга лежит на столЕ
Directional: Ich lege den Buch auf den Tisch. (I place the book on the table.) - Я кладу книгу на стол

Only in German the Dative is the equivalent of Russian Locative for this purpose.

Кого ты пригласил на дне рождения? means Whom did you invite AT your birthday? that is the invitation was handed while at the birthday party.

The difference can be highlighted with the following sentence

На моём дне рождения ^Locative мой друг пригласил меня на свой день рождения ^Accusative

At ^Locative my birthday party my friend invited me to ^Accusative his birthday party

So when you need to decide what case to use you may be guided by questions Где? (Where?) and Куда? (Whereto/whither?). The first implies a place/static condition and so requires Prepositional/Locative, the second implies direction/goal/destination and therefore requires Accusative.

Other examples

Cидя ^Where? в комнате ^Locative, я смотрю ^Whereto? в окно ^Accusative

Я встал на руки ^Accusative и стою на руках ^Locative

In Russian there're 4 prepositions with varying case governance depending on the type of activity: на, в, под, за

                                               НА / В           ПОД / ЗА

Positional                   Prep./Loc.             Instr.

Directional                             Accusative

Answer 2

Consider it as a party, a birthday party. If you are asked "Where were you yesterday?" – At Tamara's party.На дне рождения.(location, place). When you invite people to your party, to visit a place, an event, it's like they will go to your place, movement, приглашаю на день рождения (accusative - день).Compare it with location --movement/direction (at school – в школе, to school – в школу).

Мы были на празднике. Он пригласил нас на праздник.Мы были в театре. Мы ходили в театр. Она пригласила нас в театр.

You can say Кого ты пригласил на дне рождения потанцевать? Who did you invite to dance at the party?

Answer 3

It is дне because день is in the prepositional case (предложный падеж) with на; it indicates the location, where you are.
You cannot say "Кого ты пригласил на дне рождения?" because you want to have на + винителный падеж (accusative): invite TO your birthday.

Answer 4

The word "день" is declinable in this situation - на днЕ рождениЯ because it's Предложный падеж. The question for word день is на чём? - на дне and than the second question is to word "рождение" - на дне ЧЕГО? рождениЯ