Learn Hardcore Russian: Я не смогу прийти сегодня вечером.

Смочь is the perfective counterpart of мочь (to be able). Perfective verbs in Russian do not have a present tense, so я смогу (“I will be able”) is a simple future form. Adding не gives не смогу = “I will not be able.”

Why is прийти in the infinitive after смогу?

Modal verbs like мочь/смочь (can, be able) are followed by a second verb in the infinitive. Therefore смогу прийти literally means “I will be able to come.”

Why is прийти perfective, and could I use the imperfective приходить here?

Прийти is the perfective form, indicating a single, completed action (arriving once). The imperfective приходить describes repeated or ongoing actions. Since you’re talking about one arrival tonight, you use прийти. Saying не смогу приходить would imply habitual or continuous coming, which doesn’t fit a one‑time event.

What case is вечером, and how does сегодня вечером function in the sentence?

Вечером is the instrumental singular of вечер (evening), used adverbially to indicate time. Сегодня вечером = “this evening” is a time adverbial phrase telling us when the action happens. Russian word order is flexible, so you could also say Сегодня вечером я не смогу прийти without changing the basic meaning.

Can I say Я не могу прийти сегодня вечером instead of не смогу? What’s the difference?

Yes. Я не могу прийти сегодня вечером uses present tense, imperfective не могу (I cannot), but it’s commonly used for future events with time markers. Subtle distinctions: • не могу (present, imperfective) – more colloquial/familiar; can feel less formal.
• не смогу (future, perfective) – more definite/formal; emphasizes a completed inability in the future.

What’s the difference between прийти and приехать?

Both mean “to arrive/come,” but:
• прийти (perfective of приходить) – “to come on foot.”
• приехать (perfective of приезжать) – “to arrive by vehicle” (car, train, etc.).
Use прийти if you arrive walking, приехать if by transport.

Where does the stress fall in смогу and прийти?

• смогу – stress on the second syllable: смоГУ.
• прийти – stress on the second syllable: приЙТИ.

Does moving сегодня вечером to the front change the meaning? For example, Сегодня вечером я не смогу прийти.

You can freely move сегодня вечером to the front. Сегодня вечером я не смогу прийти places emphasis on when you can’t come but does not change the essential meaning.