Learn Hardcore Russian: Я сел на диван, затем прочитал письмо. - I sat on the couch, then I read the letter.

The verb сел is the past tense masculine singular of the perfective infinitive сесть (“to sit down”). Its imperfective counterpart is садиться, which you’d use for ongoing or habitual actions of sitting down.

Why is сел used here instead of садился?

Because сел (from perfective сесть) indicates a single, completed action. садился (imperfective) would imply the process of sitting down or a repeated/habitual action rather than one finished event.

Why is на диван in the accusative case, and what form would you use to say you’re already sitting on the couch?

When на expresses motion toward or onto something, Russian uses the accusative case. To describe location (already on the couch), you switch to the prepositional case: на диване.

Why is я omitted before прочитал письмо in the second clause?

Russian is a pro-drop language: if the subject is clear and stays the same, you can drop the pronoun. Since “I” is already established in the first clause, я isn’t needed again.

What does затем mean, and how does it differ from потом or после этого?

затем means “then” or “after that,” often used in a slightly more formal or narrative context than потом (“then/later”). после этого (“after this”) is more explicit and sometimes stronger, emphasizing that one action finished before the next began.

Could you replace затем with потом, and would that change the tone?

Yes. Я сел на диван, потом прочитал письмо. sounds more conversational. Using затем gives a more formal or literary flavor.

Why is прочитал in the perfective, and how would you say “I was reading the letter”?

прочитал (perfective) shows that the act of reading the letter was completed. To express an ongoing past action, use the imperfective читать: Я читал письмо (“I was reading the letter”).

Why is письмо in the accusative case, and does its form change from the nominative?

письмо is the direct object of прочитал, so it takes the accusative. As an inanimate neuter noun, its accusative form is identical to the nominative, so it remains письмо.

Why is there a comma before затем, and is it always required between such clauses?

The comma separates two independent clauses and marks the pause before the sequence adverb затем. In written or formal Russian it’s standard. In very short or colloquial statements it might sometimes be dropped, but generally you include it.

Can you move затем to the beginning of the sentence, and how would that sound?

Yes. Затем я сел на диван и прочитал письмо. This fronting of затем emphasizes the temporal link and gives a slightly more formal or narrative tone.