Choosing Aspect: A Decision Guide | Czech Grammar

This page is the one to keep open while you write or speak. Everywhere else in the aspect section we explain why the system works the way it does; here we turn that understanding into a fast, repeatable decision procedure. Run a sentence through the questions below in order, and the first one that fits decides your aspect. The deepest thing to remember is the one most learners get backwards: aspect is about completion and boundedness, not about time. A perfective is not "the past tense" and an imperfective is not "the long action" — they are two ways of packaging an action, and that packaging is what you are choosing.

The decision tree

Ask these questions in order. Stop at the first "yes."

1. Is the action happening right now, in progress?

If you mean "I am doing it at this moment," you have no choice: it must be imperfective. The perfective has no genuine present tense (its present-tense forms point to the future), so anything anchored to now is imperfective by default.

Právě teď vařím večeři.

Right now I'm cooking dinner.

2. Is it habitual, repeated, or a general truth?

Routines, habits, and things that happen over and over are imperfective, because a repeating pattern is open-ended and unbounded — it is a process, not one completed whole.

Každý den čtu noviny u snídaně.

Every day I read the paper at breakfast.

3. Is it the start or the end phase of an action?

After a phase verb — začít (begin), přestat (stop), zůstat (remain doing) — the complement is imperfective, always. You cannot begin or end a completed whole; you can only begin or end a process. (See phase verbs require the imperfective.)

Začal jsem se učit česky loni.

I started learning Czech last year.

4. Is it a single, completed whole with a result?

If you are reporting one bounded event that reached its endpoint — something got done, finished, achieved — that is the perfective. This is its home: the one-off act, the result you can now point to.

Konečně jsem dočetl tu knihu.

I finally finished reading that book.

5. Is it a one-off future event, or an ongoing/repeated future?

In the future, the fork is between the perfective present-form future (a single completed event to come) and budu + imperfective infinitive (a future activity that is ongoing or repeated). "I'll write it (and finish)" is napíšu; "I'll be writing / I'll write regularly" is budu psát.

Zítra ti napíšu e-mail.

Tomorrow I'll write you an email. (one completed act)

Příští rok budu psát diplomovou práci.

Next year I'll be writing my thesis. (ongoing future activity)

💡

The order matters. Questions 1–3 force the imperfective regardless of anything else; only if all three are "no" do you weigh completion (question 4) and the future fork (question 5). When in doubt, ask: am I inside a process, or looking at a finished whole?

Cue words that tip the scale

Czech sprinkles its sentences with adverbs that strongly favour one aspect. They are not absolute rules, but they are reliable signals — when you see them, your aspect is usually already decided.

Lean imperfective	Meaning	Lean perfective	Meaning
často	often	najednou	suddenly, all at once
vždycky	always	konečně	finally
každý den	every day	už	already
obvykle	usually	náhle	abruptly
pořád	constantly, still	hned	right away, at once
celý den	all day (duration)	za hodinu	in an hour (within)

The left column points at repetition or duration (the imperfective's territory); the right column points at a single decisive moment or completion (the perfective's). Watch them work:

Často jezdíme na chatu.

We often go to the cottage. (často → imperfective, a repeated habit)

Najednou se rozsvítilo světlo.

Suddenly the light came on. (najednou → perfective, one abrupt event)

Celý den jsem uklízel byt.

I spent all day cleaning the flat. (celý den → imperfective, duration measured)

Za hodinu uklidím byt.

I'll clean the flat in an hour. (za hodinu → perfective, completion within a span)

Note the neat contrast in the last two: celý den ("all day", measuring a stretch the action filled) wants imperfective, while za hodinu ("within an hour", framing a completion) wants perfective. The very same verb (uklízet / uklidit) goes either way depending on which adverb frames it.

Completion, not time, is the deciding factor

The single biggest error English speakers make is assuming aspect tracks tense: that the perfective is somehow "more past" or the imperfective "more present." It does not. Both aspects appear in the past, and the choice between them in the past is entirely about whether you are reporting a completed whole or describing a process — never about how long ago it was.

Včera jsem psal úkol tři hodiny.

Yesterday I worked on my homework for three hours. (process, duration — imperfective)

Včera jsem napsal úkol a poslal ho učiteli.

Yesterday I did my homework and sent it to the teacher. (completed result — perfective)

Same day, same homework, same past tense — opposite aspects, because the first measures the activity and the second reports the result. Time is identical; packaging differs.

💡

Strip out the time word and ask the only question that matters: do I mean the activity (inside, unfolding, lasting, repeating) or the finished whole (one bounded event with its result)? Activity → imperfective. Whole → perfective.

Three quick decisions, reasoning shown

Walk these through the tree yourself before reading the verdict.

1. "Every evening she read to the children." → Question 2: habitual, repeated. → imperfective.

Každý večer dětem ČETLA.

Every evening she read to the children.

2. "She finally finished the novel last night." → Question 4: single completed result, flagged by konečně. → perfective.

Včera večer ten román konečně DOČETLA.

Last night she finally finished the novel.

3. "Tomorrow I'll be studying all day." → Question 5: ongoing future activity, with celý den confirming duration. → budu + imperfective.

Zítra se budu celý den UČIT.

Tomorrow I'll be studying all day.

Notice how each one is settled by a different question, and how the cue word (každý večer, konečně, celý den) corroborates the verdict. That is the workflow: run the tree, let the cue word confirm.

When both seem possible

Sometimes either aspect is grammatical and the difference is one of focus rather than right-versus-wrong. "I read that article" can be četl jsem ten článek (I was reading it / I read at it, focus on the activity) or přečetl jsem ten článek (I read it through, focus on completion). Neither is an error; they answer different questions — what were you doing? versus did you get through it? When you genuinely hesitate, pick the aspect that matches what you want to foreground: the doing, or the done. For a fuller side-by-side treatment of the contrast, see perfective vs imperfective.

Common Mistakes

❌ Teď udělám domácí úkol a je to hotové.

Wrong for 'I'm doing it now' — udělám is a future completion; a present-moment action must be imperfective (dělám).

✅ Teď dělám domácí úkol.

I'm doing my homework right now.

❌ Každý den napíšu deník.

Wrong — a daily habit is imperfective; the perfective napíšu claims one specific completed writing, clashing with 'every day'.

✅ Každý den si píšu deník.

I write in my diary every day.

❌ Budu přečíst tu knihu o víkendu.

Wrong — a perfective can't follow budu; for a one-off completed future use the perfective present form přečtu.

✅ Přečtu tu knihu o víkendu.

I'll read that book over the weekend.

❌ Začal jsem udělat ten projekt.

Wrong — after a phase verb the complement is imperfective: you can't begin a completed whole.

✅ Začal jsem dělat ten projekt.

I started working on that project.

The thread is always the same. Run the tree in order; the first "yes" decides; and never let a time word fool you into thinking aspect is about when rather than about completion.

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