Quick answer
Every Russian verb is either imperfective (process, repetition, general fact) or perfective (one completed act). Most verbs come as a pair.
What each aspect does
| Imperfective | Perfective |
|---|---|
| process: Я чита́л весь ве́чер. | result: Я прочита́л кни́гу. |
| repetition: Я чита́ю ка́ждый день. | one occasion: Я прочита́л э́то вчера́. |
| general fact: Ты чита́л Толсто́го? | completion: Ты прочита́л письмо́? |
| present tense exists | no present tense at all |
The last row is the key structural fact: a perfective verb in the “present” form is always a future. Я прочита́ю means “I will read it”, never “I am reading”.
How pairs are built
| Method | Imperfective | Perfective |
|---|---|---|
| prefix added | чита́ть | прочита́ть |
| suffix changed | реша́ть | реши́ть |
| different word | говори́ть | сказа́ть |
| stress moves | покупа́ть | купи́ть |
There is no rule that predicts which method a given verb uses, which is why aspect pairs are learned together, as one item: чита́ть — прочита́ть.
The three tenses
Imperfective: past чита́л, present чита́ю, future бу́ду чита́ть. Perfective: past прочита́л, future прочита́ю — and nothing in between. Six forms in total, which is fewer than English has.
Where aspect is not a choice
Three places force your hand. Negative commands take the imperfective: не забыва́й. Verbs of beginning, continuing and finishing take an imperfective infinitive: начина́ю чита́ть. And after нельзя́, the imperfective means “not allowed” while the perfective means “impossible”.
Typical mistakes
Я бу́ду прочита́ть.
Я прочита́ю. / Я бу́ду чита́ть.
A perfective verb has no бу́ду future.
Я прочита́ю ка́ждый день.
Я чита́ю ка́ждый день.
A habit is imperfective.
Check yourself
What does Я прочита́ю mean?