Learn Hardcore Ukrainian: Він залишив свій підпис на чековій книжці, і я зберіг копію. - He left his signature on the checkbook, and I kept a copy.

In Ukrainian, свій is a reflexive possessive pronoun that refers back to the subject of the sentence. In Він залишив свій підпис, using свій indicates that the signature belongs to him, the same person performing the action. Using його would imply possession by someone else, so свій is the correct choice when the owner is the subject.

Why is the noun чекова книжка changed to чековій книжці in this context?

The change occurs because the noun is used with the preposition на, which in this case requires the prepositional case to indicate location. Чековій книжці is the prepositional form of чекова книжка, showing that the signature was left on the checkbook.

What case is копію in, and why is it used in that form?

Копію is in the accusative case because it is the direct object of the verb зберіг (I kept). In Ukrainian, the direct object that receives the action of the verb is typically in the accusative case.

Is the comma before і necessary in this sentence, and what does it indicate?

Yes, the comma before і is necessary. It separates the sentence into two independent clauses: the first clause details what he did (Він залишив свій підпис на чековій книжці) and the second clause explains what I did (я зберіг копію). The comma indicates a pause between these two complete thoughts as required by Ukrainian punctuation rules.

How are the two clauses in the sentence structured and connected?

The sentence is a compound sentence consisting of two independent clauses linked by the coordinating conjunction і (and). The first clause, Він залишив свій підпис на чековій книжці, presents one complete idea, and the second clause, я зберіг копію, offers another. Together, they form a clear relationship between two related actions performed by different subjects.