Some actions are inherently repeatable strings of identical little events: shouting is a series of cries, knocking is a series of knocks, waving is a series of waves. Ukrainian has a dedicated tool for slicing one single instance out of such a string — the suffix -ну-. From крича́ти "be shouting" it makes кри́кнути "give one shout"; from сту́кати "be knocking" it makes сту́кнути "knock once"; from маха́ти "wave" it makes махну́ти "give one wave." These -ну- verbs are called semelfactives (from Latin semel "once"), they are perfective, and they are punctual — a single, instantaneous act. They sit opposite the multiplicative imperfectives in -а-, which name the action as an open, repeated process.
The semelfactive ↔ multiplicative contrast
The two members of a semelfactive pair are not "imperfective process / perfective whole" the way a normal pair is. They are one instance versus many instances: the -ну- verb is a single bounded flick of the action, while the -а- verb is the action conceived as iterated or continuous. Lining them up:
| Multiplicative (impf, -а-) | Semelfactive (pf, -ну-) | Meaning |
|---|---|---|
| крича́ти | кри́кнути | shout / give one shout |
| сту́кати | сту́кнути | knock / knock once |
| маха́ти | махну́ти | wave / give one wave |
| кива́ти | кивну́ти | nod / nod once |
| ковта́ти | ковтну́ти | swallow / take one gulp |
| блища́ти | блисну́ти | glint / flash once |
| стриба́ти | стрибну́ти | jump / give one jump |
| зітха́ти | зітхну́ти | sigh / give one sigh |
Хтось сту́кнув у две́рі — оди́н раз, ти́хо. Я прислу́халася, але́ бі́льше ніхто́ не сту́кав.
Someone knocked at the door — once, quietly. I listened, but no one knocked any more. (сту́кнув semelfactive, one knock; сту́кав multiplicative, repeated knocking.)
Не кричи́ на ме́не! — Я не кричу́, я кри́кнув оди́н раз з переля́ку.
Don't shout at me! — I'm not shouting, I gave one shout out of fright. (кричу́/кричи́ multiplicative, ongoing; кри́кнув semelfactive, a single cry.)
По́тяг ру́шив, і вона́ махну́ла руко́ю на проща́ння, а по́тім ще до́вго маха́ла вслід.
The train started, and she gave one wave goodbye, and then waved after it for a long time. (махну́ла semelfactive, one wave; маха́ла multiplicative, sustained waving.)
These -ну- verbs are perfective and punctual
Because a semelfactive names a single bounded act, it behaves like any perfective: it has no present tense (its present-form conjugation is a future), and it shines in narration, where it advances the story by one sharp event. сту́кнути, кивну́ти, блисну́ти are the verbs you reach for when something happens suddenly, once, and then it's over.
Він зазирну́в у кімна́ту, кивну́в мені́ й ти́хо причини́в две́рі.
He glanced into the room, gave me a nod, and quietly pulled the door to. (a chain of punctual perfectives — зазирну́в, кивну́в, причини́в — each one event advancing the narrative.)
Раптом у те́мряві блисну́ло сві́тло фар, і за мить усе́ зни́кло.
Suddenly the glare of headlights flashed in the dark, and a moment later everything vanished. (блисну́ло semelfactive, a single flash; contrast блища́ло 'was glinting' for a sustained shimmer.)
Я ковтну́в води́, щоб заспоко́їтися, і поча́в говори́ти.
I took a gulp of water to calm down, and started to speak. (ковтну́в semelfactive, one swallow; ковта́ти would be 'be swallowing / keep swallowing'.)
Watch out: not every -ну- verb is a semelfactive
The -ну- suffix has more than one life. Two other groups wear the same suffix but behave differently, and confusing them is a common trap.
1. Inceptive / change-of-state -ну- verbs describe entering a state, not a single repeatable act. These are often imperfective, with the state building gradually, and many of them drop the -ну- in the past tense for the masculine (here -ну- is part of the verb stem, not a semelfactive marker):
- ме́рзнути "to be freezing, get cold" → past мерз, ме́рзла, ме́рзло (the -ну- disappears in мерз).
- со́хнути "to dry (out)" → past сох, со́хла.
- ги́нути "to perish" → past гинув / гинула (here the -ну- usually stays, but the verb is still a process, not a semelfactive).
Ми пів годи́ни ме́рзли на зупи́нці, поки́ при́їхав авто́бус.
We were freezing at the stop for half an hour until the bus came. (ме́рзли imperfective state; note the past мерз / ме́рзли drops the -ну-.)
2. Plain perfectives in -ну- that aren't "once" at all — поверну́ти "to turn / return," відпочи́ну (perfective of відпочива́ти "rest"), and many motion verbs. Here -ну- is just part of the perfective stem, with no semelfactive flavour. Don't read "once" into every -ну-; read it only where there's a clear multiplicative -а- partner (сту́кати/сту́кнути).
Я на хвили́нку відпочи́ну й допоможу́ тобі́ з валі́зами.
I'll rest for a minute and help you with the suitcases. (відпочи́ну perfective future — a -ну- verb, but not a semelfactive: it has no *відпочи́кати multiplicative partner.)
Source-language comparison
For an English speaker, the semelfactive captures a distinction English makes only with extra words. "He knocked" is ambiguous in English — one knock or several? Ukrainian forces the choice into the verb: сту́кнув = exactly one knock, сту́кав = was knocking / knocked repeatedly. Where English says "give a shout," "have a sip," "take one look," Ukrainian packs the "one" into the -ну- suffix: кри́кнути, ковтну́ти, гля́нути. The mirror-image: where English says "keep knocking," "be waving," Ukrainian uses the -а- multiplicative сту́кати, маха́ти. So the punctual/iterative contrast that English marks lexically ("once" vs "keep V-ing") Ukrainian marks morphologically, inside the verb.
For a Russian speaker, the category is the same (Russian кри́кнуть / крича́ть, сту́кнуть / сту́кать). Relearn the Ukrainian forms and stress (кри́кнути, сту́кнути, ковтну́ти, блисну́ти) and note that Ukrainian keeps a strong native set like зітхну́ти, кивну́ти in everyday use.
Common Mistakes
❌ Він до́вго кри́кнув на ді́тей.
A semelfactive is a single instant — it can't be 'long'. For sustained shouting use the multiplicative imperfective: Він до́вго крича́в на ді́тей.
✅ Він до́вго крича́в на ді́тей.
He shouted at the children for a long time. (крича́в multiplicative, sustained.)
❌ Я за́раз сту́кну тричі. (semelfactive for three knocks)
One -ну- act = one knock, so 'three times' contradicts it. Use the multiplicative: Я за́раз сту́катиму тричі, or simply Я сту́кну тричі only if you mean three separate single knocks made as one signal — but for repeated knocking, сту́кати.
✅ Я по́стукаю / сту́катиму, поки́ не відчи́нять.
I'll keep knocking until they open. (the iterative, not a single сту́кнути.)
❌ Учо́ра він ме́рзнув на моро́зі. (keeping -ну- in the past)
The inceptive verb ме́рзнути drops -ну- in the masculine past: Учо́ра він мерз на моро́зі.
✅ Учо́ра він мерз на моро́зі.
Yesterday he was freezing in the cold. (past мерз, no -ну-.)
❌ Пташка́ маха́ла кри́льми оди́н раз і зле́тіла.
'One wave' is a single act — use the semelfactive, not the multiplicative: Пташка́ махну́ла кри́льми оди́н раз і зле́тіла.
✅ Пта́шка махну́ла кри́льми й зле́тіла.
The bird gave one flap of its wings and flew off. (махну́ла semelfactive, a single beat.)
Key Takeaways
- The suffix -ну- carves a semelfactive — one instantaneous instance of a repeatable action: кри́кнути "give one shout," сту́кнути "knock once," махну́ти "give one wave," кивну́ти "nod once," ковтну́ти "take one gulp," блисну́ти "flash once."
- Semelfactives are perfective and punctual: no present tense, perfect for narration, the opposite of their multiplicative -а- imperfectives (крича́ти, сту́кати, маха́ти, кива́ти) which name the action as a repeated or ongoing process.
- The punctual/iterative contrast English marks with words ("once" vs "keep V-ing") Ukrainian marks inside the verb.
- Beware other -ну- verbs: inceptive ones name a state and may drop -ну- in the past (ме́рзнути → мерз, со́хнути → сох); some -ну- verbs are plain perfectives (поверну́ти, відпочи́ну) with no "once" meaning. Read -ну- as "semelfactive" only where there's a clear -а- multiplicative partner.
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- What the Perfective MeansA2 — The perfective (доко́наний вид) views the action as a single bounded whole: a completed result (прочита́в, написа́в), a step in a narrative chain (прийшо́в, сів, відкри́в), an onset (заспіва́в, пішо́в), or a finished future result (прочита́ю). Its defining idea is BOUNDEDNESS, it drives narrative sequences, and — the fact that catches everyone — it has NO present: прочита́ю IS the future.
- What the Imperfective MeansA2 — The imperfective (недоко́наний вид) is the aspect of process, habit, simultaneity, and — crucially — of simply naming an activity without caring whether it finished: чита́ти, чита́ю, чита́в. It is the ONLY aspect with a real present, the default for repeated and backgrounded action, and the form Ukrainian uses to ask whether something was ever done at all (Ти диви́вся цей фільм? 'have you seen this film?').
- Biaspectual and Aspect-Only VerbsB2 — Not every verb has a clean imperfective/perfective pair: biaspectual verbs (двовидові) like телефонува́ти, організува́ти and атакува́ти carry BOTH aspects in one form and let context decide; imperfectiva tantum (бу́ти, ма́ти, могти́, хоті́ти, зна́ти) have no perfective at all; perfectiva tantum (опини́тися, розговори́тися) have no imperfective; and the semelfactive -ну- verbs (сту́кнути, кри́кнути, махну́ти) express a single instantaneous act against a multiplicative imperfective (сту́кати, крича́ти, маха́ти).
- Forming Aspect Pairs: Suffixes and StemsB1 — The other half of the pairing system: deriving an IMPERFECTIVE from a perfective by suffix, above all the -а-/-ува-/-ову- imperfectivizing suffixes — да́ти→дава́ти, купи́ти→купува́ти, показа́ти→пока́зувати, забу́ти→забува́ти, відкри́ти→відкрива́ти. Plus consonant mutations (зустрі́ти→зустріча́ти), root-vowel alternations (зібра́ти→збира́ти, поме́рти→помира́ти), and the handful of suppletive pairs that must simply be memorised (бра́ти/взя́ти, говори́ти/сказа́ти).
- High-Frequency Aspect Pairs to MemorizeA2 — A curated reference list of the ~40 most useful imperfective/perfective pairs, grouped by HOW they are formed — prefix pairs (чита́ти/прочита́ти), suffix pairs (купува́ти/купи́ти), suppletive pairs (бра́ти/взя́ти, говори́ти/сказа́ти), and root-vowel pairs (збира́ти/зібра́ти) — so you can absorb whole clusters at once instead of memorising every verb in isolation.