Learn Hardcore Russian: Мой друг идёт на вечеринку.

In Russian, adjectives—including possessives—must agree in gender, number, and case with the noun they modify. Since друг (friend) is masculine and in the nominative case (as the subject of the sentence), the masculine form мой is used. If the noun were feminine (for example, подруга), you would use моя instead.

How is the verb идёт formed, and what does it tell us about the action being described?

The verb идёт is the third person singular form of the imperfective verb идти in the present tense. This form indicates that the action—the friend going to the party—is currently in progress. Using the imperfective aspect here emphasizes that the action is ongoing rather than complete.

Why is the noun вечеринка transformed into вечеринку in this sentence?

The change from вечеринка to вечеринку is due to the accusative case. In Russian, when the preposition на expresses movement toward a destination—as in "going to a party"—the following noun must be in the accusative case. Thus, вечеринка becomes вечеринку to reflect that it is the destination of the action.

What role does the preposition на play in this sentence, and how does it affect the form of вечеринка?

In this sentence, на indicates direction or movement toward a destination. When is used to express movement (as opposed to a static location), it requires that the noun that follows be in the accusative case. That’s why takes the accusative form , clearly marking it as the destination of the friend's action.