Serbian verb aspect: perfective and imperfective, explained for English speakers

Two verbs for one action

Look up "to buy" in a Serbian dictionary and you get two words: kupovati and kupiti. Both mean to buy, and neither is a variant of the other. Kupovati is the buying as an activity: something you do regularly, are in the middle of, or that takes time. Kupiti is the buying as a completed act: one purchase, done. Serbian makes you choose every time you use the verb, and the choice is called aspect. The activity verb is imperfective, the completed one perfective.

English has the same distinction but hides it in the tenses. I was buying, I used to buy and I buy every week are imperfective ideas; I bought it and I have bought it are perfective ones. Serbian moves that information out of the tense and into the verb itself, which is why it can get by with so few tenses.

Which one a sentence wants

The test that works most of the time: is the sentence about an action as a whole, finished, with a result? Then perfective. Is it about the action going on, repeating, or being the kind of thing you do? Then imperfective.

The idea	Aspect	Serbian
I bought a ticket (one act, done)	perfective	Kupio sam kartu.
I was buying a ticket when you called	imperfective	Kupovao sam kartu kad si zvao.
I buy bread every morning	imperfective	Kupujem hleb svako jutro.
I will buy it tomorrow (once)	perfective	Kupiću ga sutra.
I will be buying things all day	imperfective	Kupovaću ceo dan.
Buy milk! (one errand)	perfective	Kupi mleko!
Don't buy that! (a general warning)	imperfective	Ne kupuj to!

Words like svaki dan (every day), često (often), dugo (for a long time) and dok (while) call for the imperfective. Words like jednom (once), odjednom (suddenly), već (already) and a sequence of events call for the perfective. Negative commands are usually imperfective, which surprises learners: Ne kupuj, not Ne kupi.

How the pairs are formed

There is no single rule, but four patterns cover most pairs.

A prefix makes an imperfective perfective. pisati to write, napisati to write and finish; čitati to read, pročitati to read through; jesti to eat, pojesti to eat up; piti to drink, popiti to drink up. The prefix is the commonest way, and the dictionary form of a beginner's verb is usually the imperfective one.

A suffix makes a perfective imperfective. kupiti to buy, kupovati; dati to give, davati; platiti to pay, plaćati; ostati to stay, ostajati. Here the short verb is the perfective one and the long one the activity.

A change in the stem. doći to come, dolaziti; ući to enter, ulaziti; početi to begin, počinjati; uzeti to take, uzimati.

Two unrelated verbs. reći or kazati to say, against govoriti to speak; and a handful of others.

There is a complication worth knowing about early. A prefix often does more than perfectivise: pisati gives napisati (write to the end) but also potpisati (sign), prepisati (copy), opisati (describe). Each of those perfectives then grows its own imperfective, potpisivati, prepisivati, opisivati. That is how one root becomes a family of a dozen verbs, and why learning roots pays off.

The two traps

The present tense of a perfective verb is not a present. Kupim exists, but it does not mean I am buying, because a completed act cannot be happening right now. It means something like "once I buy" and lives in subordinate clauses: Kad kupim kartu, zvaću te, when I have bought the ticket I will call you. For anything happening now, use the imperfective: Kupujem kartu. This is the single most frequent aspect mistake English speakers make, because the perfective is often the verb they learned first.

The past tense needs the choice too. English speakers reach for one past form and use it everywhere. In Serbian Kupovao sam and Kupio sam are both past, and a story told with the wrong one sounds either unfinished or oddly jerky. Background and habit take the imperfective; the events that move the story forward take the perfective. Sedeo sam u kafiću i čitao novine. Odjednom je ušao Marko. I was sitting in the café reading the paper. Suddenly Marko came in.

How to learn it

Learn verbs in pairs from the start, even if the second one waits a few weeks: kupovati / kupiti, pisati / napisati. When you write a sentence, decide whether the action is a whole event or an ongoing one before you pick the verb. Then let the correction tell you when your instinct was wrong. The instinct is the goal; the rule above is a crutch until you have it, and a few hundred corrected sentences later the pairs stop being a choice and become a single verb with two shapes, which is what they are to a native speaker.