Can: Мочь vs Уметь | Russian Grammar

English has one word, can, for two very different ideas: knowing how to do something (I can swim — I learned how) and being able to do it right now (I can swim today, the water's warm — circumstances allow it). Russian refuses to blur these. It uses уме́ть (umét') for the learned skill and мочь (moch') for the possibility in a given moment. Choosing wrongly doesn't just sound off — it changes the meaning. This page sorts the two verbs, drills the irregular conjugation of мочь, and ends with the one mistake that instantly marks a sentence as non-native.

уме́ть — to know how to (a skill)

уме́ть is about ability you acquired by learning: swimming, driving, cooking, playing an instrument, speaking a language. It answers "do you have the know-how?", not "can you do it this instant?". It is a perfectly regular first-conjugation -ть verb.

Person	уме́ть (imperfective)
я	уме́ю
ты	уме́ешь
он / она́	уме́ет
мы	уме́ем
вы	уме́ете
они́	уме́ют

уме́ть is followed by an infinitive, almost always imperfective (the skill is an ongoing, general capacity, not a single completed act).

Я уме́ю пла́вать, но не о́чень бы́стро.

I can swim, but not very fast. (уме́ю + imperfective пла́вать — the learned skill of swimming)

Ты уме́ешь гото́вить?

Can you cook? / Do you know how to cook? (asking about a skill, not about availability tonight)

Она́ уме́ет води́ть маши́ну с восемна́дцати лет.

She's known how to drive since she was eighteen. (a skill held over time)

The perfective partner суме́ть (sumét') means "manage to / succeed in" a one-off effort: Я суме́л его́ убеди́ть — "I managed to convince him." That's a different shade (success at a single task), covered with the past/future modal forms on ability in the past and future.

мочь — to be able to (possibility in the moment)

мочь is about whether something is possible right now, given the circumstances: your physical state, your schedule, permission, the situation. It does not mean you have a skill — it means nothing is stopping you (or, negated, that something is). мочь is irregular, with a г/ж consonant alternation running through the conjugation.

Person	мочь (imperfective)
я	могу́
ты	мо́жешь
он / она́	мо́жет
мы	мо́жем
вы	мо́жете
они́	мо́гут

Notice the shape: the я and они́ forms keep г (могу́, мо́гут), while everything in between switches to ж (мо́жешь, мо́жет, мо́жем, мо́жете). The stress also shifts — it lands on the ending in могу́ but on the stem everywhere else (мо́жешь, мо́жет…). This is a small irregular set you simply memorize; there's no rule that derives the ж from the г here, only a sound change frozen into the paradigm.

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The trap inside the paradigm is the ты form. It is мо́жешь with ж, never *могешь. The г only survives in могу́ and мо́гут — the two "edge" forms. If you can rattle off "могу́, мо́жешь… мо́гут" with that г–ж–г pattern, you've got the hardest part of this page.

мочь takes an infinitive (of either aspect, depending on what you mean) or stands alone in short replies.

Я могу́ прийти́ за́втра, е́сли хо́чешь.

I can come tomorrow if you like. (possibility — nothing prevents it; perfective прийти́ for the single planned visit)

Ты мо́жешь помо́чь мне с дива́ном?

Can you help me with the sofa? (asking whether circumstances allow it — are you free, are you willing)

Я не могу́ откры́ть дверь — её, ка́жется, за́перли.

I can't open the door — it seems to have been locked. (not a lack of skill; an obstacle in the situation)

— Ты придёшь? — Не зна́ю, посмо́трим, мо́жет, и смогу́.

— Will you come? — I don't know, we'll see, maybe I'll be able to. (perfective future смогу́ — 'manage to')

The perfective смочь (future смогу́, смо́жешь… смо́гут, past смог / смогла́ / смогло́ / смогли́) is the natural way to say "will be able to / managed to" on a specific occasion.

The contrast, side by side

Put the same English sentence through both verbs and the meanings split apart:

Russian	What it actually says
Я уме́ю игра́ть на гита́ре.	I know how to play the guitar (I learned; it's a skill).
Я могу́ сыгра́ть сейча́с.	I can play right now (I'm free / willing / nothing's stopping me).

Я уме́ю води́ть, но сего́дня не могу́ — вы́пил вина́.

I know how to drive, but I can't today — I've had wine. (уме́ю = the skill is intact; не могу́ = circumstances now forbid it)

This sentence is impossible to translate with a single "can" twice without sounding strange in English too — which is exactly why Russian keeps the verbs apart. The skill (уме́ю) doesn't disappear because you had a glass of wine; what disappears is the possibility (могу́) of acting on it tonight.

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A quick test: if you could insert "know how to" in English, use уме́ть. If you could insert "be in a position to / be able to right now", use мочь. "I can speak Russian" = уме́ю (I learned it). "Can you speak up?" = мо́жешь (are you able to, right now).

мо́жно — the impersonal cousin

Alongside the verb мочь sits the impersonal word мо́жно ("it's allowed / it's possible"). It is not conjugated and has no subject; the person, if mentioned, goes in the dative. Use it for permission and general possibility:

Здесь мо́жно фотографи́ровать?

Is it allowed to take photos here? (general permission — no personal subject)

Мне мо́жно войти́?

May I come in? (dative мне; asking permission for myself)

Мо́жно вопро́с?

May I ask a question? (a fixed polite formula — мо́жно + a noun)

мо́жно overlaps with мочь in the permission sense — Мо́жно мне войти́? and Могу́ я войти́? both ask "may I come in?", with мо́жно being the everyday choice and Могу́ я…? a touch more formal. The full treatment of мо́жно and its negative нельзя́ — including the crucial way нельзя́ changes meaning with the aspect of the following verb — is on Можно, Нельзя.

Common Mistakes

❌ Я могу́ пла́вать.

Incorrect for 'I know how to swim' — this says 'I'm physically able to swim right now' (e.g. the water's safe, I'm not injured). For the skill, use уме́ю.

✅ Я уме́ю пла́вать.

I can / know how to swim. (the learned skill → уме́ть)

❌ Ты могешь помо́чь?

Incorrect — the ты form is мо́жешь with ж, not *могешь; г only survives in могу́ and мо́гут.

✅ Ты мо́жешь помо́чь?

Can you help? (мо́жешь — ж form)

❌ Я уме́ю прийти́ за́втра.

Incorrect — coming tomorrow isn't a skill; it's a possibility in the situation. Use могу́.

✅ Я могу́ прийти́ за́втра.

I can come tomorrow. (possibility → мочь)

❌ Она́ мо́жет говори́ть по-ру́сски.

Misleading for 'she speaks/knows Russian' — this suggests she's able to right now (e.g. she's not too tired). For knowing the language, use уме́ет (or, idiomatically, говори́т по-ру́сски / зна́ет ру́сский).

✅ Она́ говори́т по-ру́сски.

She speaks Russian. (the idiomatic way to state a language skill)

❌ Мне могу́ войти́?

Incorrect — мочь is a conjugated verb with a nominative subject; you can't add a dative. For dative-based permission, use the impersonal мо́жно.

✅ Мне мо́жно войти́?

May I come in? (dative мне + impersonal мо́жно)

Key Takeaways

уме́ть = know how to (a learned skill): уме́ю пла́вать, уме́ет води́ть. Regular -ть conjugation (уме́ю, уме́ешь… уме́ют), followed by an imperfective infinitive.
мочь = be able to right now (possibility, permission, circumstance): могу́ прийти́, не могу́ откры́ть. Irregular with г/ж alternation: могу́, мо́жешь, мо́жет, мо́жем, мо́жете, мо́гут — г only in могу́/мо́гут.
Perfective partners: суме́ть ("manage to" a one-off effort) and смочь ("be able to / manage to" on a specific occasion, future смогу́).
мо́жно (impersonal, dative person) handles permission and general possibility: Здесь мо́жно? Мне мо́жно войти́?
The signature error is using мочь for a skill (Я могу́ пла́вать); to a Russian ear that means "I'm physically capable of swimming at this moment", not "I know how". When you mean a skill, reach for уме́ть.

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