Learn Hardcore Ukrainian: Я купив квартиру.

In Ukrainian, past tense verbs agree with the speaker’s gender. Купив is the masculine form, so it is used when the speaker is male. If a female speaker were saying the same sentence, she would say Я купила квартиру.

What case is квартиру in, and why does its ending change from -а to -у?

The noun квартира is in the accusative case because it is the direct object of the verb купив. For many feminine nouns in Ukrainian, the accusative singular ending changes to -у (from -а), so квартира becomes квартиру in this context.

What is the basic syntactical structure of the sentence Я купив квартиру?

The sentence follows a subject–verb–object order: Я (subject) + купив (verb) + квартиру (object). This is a common word order in Ukrainian, though variations are possible for emphasis.

What is the infinitive form of купив, and what does it mean?

The infinitive of купив is купити, which means to buy. In this sentence, the perfective past tense (купив) indicates that the action of buying is completed.

Is it possible to change the word order in this sentence, and if so, what might be an alternative?

Yes, Ukrainian often allows flexible word order to emphasize different parts of the sentence. For example, saying Квартиру я купив puts more emphasis on квартиру (the apartment), which might be useful if you want to stress what was bought rather than who bought it.