Learn Hardcore Czech: Můj bratr často rychle píše úkol u počítače. - My brother often writes his homework quickly at the computer.

Můj is the masculine singular form of “my” that agrees with bratr (brother), which is a masculine noun in the nominative singular (the basic dictionary form, used for the subject).

Můj bratr = my brother (subject, nominative)
Moje is used for most feminine and neuter nouns in nominative (e.g. moje sestra, my sister).
Mého bratra is genitive or accusative, not nominative. You would use it when bratr is not the subject, e.g.:
- Vidím svého / mého bratra. – I see my brother. (accusative)

In your sentence, my brother is the subject (who is doing the writing), so Můj bratr is the correct form.

What case is bratr in, and how do I know?

Bratr is in the nominative singular.

Clues:

It is the subject of the sentence (the “doer” of the action): Who writes the homework? – Můj bratr.
Czech subjects normally appear in the nominative.
The basic, dictionary form of a noun is nominative, and bratr appears exactly in that form here.

Other common forms of bratr:

bratra – accusative/genitive singular (e.g. vidím bratra, I see (my) brother)
bratrem – instrumental singular (e.g. s bratrem, with (my) brother)

What is the basic word order of this sentence, and can I move the words around?

The sentence Můj bratr často rychle píše úkol u počítače. has this structure:

Můj bratr – subject
často rychle – adverbs (how often? how?)
píše – verb
úkol – direct object
u počítače – place (location)

So the “neutral” order is:

Subject – (frequency adverb) – (manner adverb) – Verb – Object – Place.

In Czech, word order is fairly flexible, but changes of order often change the emphasis:

Můj bratr často rychle píše úkol u počítače.
Neutral: your brother often writes his homework quickly at the computer.
Často můj bratr rychle píše úkol u počítače.
Emphasizes často (often): as for “often”, it’s my brother who does this.
Můj bratr píše úkol u počítače často rychle.
Sounds a bit unnatural; the adverbs usually come before the verb.

For learners, it is safest to keep adverbs before the verb as in the original sentence.

Why is it často rychle, not rychle často?

Both často (often) and rychle (quickly) are adverbs, but they express different things:

často – frequency (how often?)
rychle – manner (how? in what way?)

The most natural order in Czech is:

frequency adverb (často, někdy, vždy, občas…)
manner adverb (rychle, pomalu, dobře, špatně…)

So:

často rychle píše sounds natural
rychle často píše sounds odd or marked; speakers might avoid it

So the usual pattern is: [how often] + [how] + verb.

What verb form is píše, and why not napíše?

Píše is:

3rd person singular
present tense
of the imperfective verb psát (to write).

You use imperfective verbs (like psát) for:

repeated actions: Můj bratr často píše úkol… – My brother often writes/does his homework.
ongoing processes: Píše úkol. – He is writing his homework (right now).

Napíše is the 3rd person singular future of the perfective verb napsat (to write/finish writing):

Můj bratr napíše úkol u počítače. – My brother will (manage to) write / will finish the homework at the computer.
→ focuses on completion of one homework, not on repetition.

Since the sentence talks about something that happens often, píše (imperfective) is correct.

How is psát → píše formed? Why is the vowel different?

The infinitive is psát. In present tense, the stem changes:

já píšu / píši – I write
ty píšeš – you write
on/ona/ono píše – he/she/it writes
my píšeme
vy píšete
oni píšou / píší

The vowel change a → í (psát → píše) is just an irregular stem alternation that many verbs in Czech have. It is not something you can “calculate”; it must be learned as part of the verb’s conjugation pattern.

Why is it úkol and not úkoly or something like domácí úkol?

Úkol means task / assignment. For school homework:

Singular: úkol – one specific task
Plural: úkoly – several tasks
domácí úkol – homework assignment (literally home task)

In ordinary speech, for school work, people often say:

domácí úkol (sg.) or domácí úkoly (pl.)
or simply úkol / úkoly, when it is clear we are talking about homework

So:

píše úkol – he is writing a (specific) homework task
píše domácí úkol – he is writing his homework assignment
dělá úkol(y) – he is doing his homework (more general, not only writing)

The sentence is grammatically fine; domácí is just a common clarifying adjective if you want to make “homework” explicit.

What case is úkol in here, and how can I tell?

In píše úkol, úkol is:

accusative singular (direct object of the verb psát).

You can recognize it because:

It answers “What is he writing?” → úkol.
It is the thing affected by the action, i.e. the direct object.
For masculine inanimate nouns like úkol, nominative and accusative singular often look the same:
- nominative: úkol (subject) – Úkol je těžký. – The task is hard.
- accusative: úkol (object) – Píše úkol. – He writes the task.

So the form úkol is ambiguous by shape, but the sentence role shows it is accusative here.

Why is it u počítače and not u počítač?

The preposition u (at, by, near) in Czech always takes the genitive case.

Nominative: počítač – computer
Genitive: počítače

After u, you must use počítače:

u počítače – (physically) at the computer

So u + genitive is a fixed pattern:

u domu – at the house
u školy – at the school
u stolu – at the table
u počítače – at the computer

U počítač would be ungrammatical, because počítač is nominative, not genitive.

What is the difference between u počítače, na počítači, and v počítači?

They all involve počítač (computer), but with different prepositions and meanings:

u počítače – at the computer (physically sitting / standing near it)
→ Focus on location next to the computer.
na počítači – literally on the computer. Often means on the computer in the sense of using the computer as a tool (e.g. working on it).
- Píše úkol na počítači. – He is writing the homework on the computer (typing, not by hand).
v počítači – in the computer, usually only for things stored inside it:
- Mám dokument v počítači. – I have the document in the computer.

Your sentence with u počítače emphasizes that he is sitting at the computer while writing.

Why are there no words like “a” or “the” in this sentence?

Czech has no articles (no equivalents of “a / an / the”). Nouns normally appear without any article-like word:

bratr – a/the brother
úkol – a/the homework task
počítač – a/the computer

Whether the meaning is definite (the brother we know) or indefinite (some brother) is understood from context and things like possessives and word order, not from an article.

In your sentence:

Můj bratr → clearly “my brother”, so it is naturally definite in English.
úkol → most naturally “his homework (task)”, because of context.

Could the sentence also be Bratr často rychle píše úkol u počítače without Můj?

Yes. Dropping můj is grammatically correct:

Bratr často rychle píše úkol u počítače. – (My) brother often quickly writes (his) homework at the computer.

In Czech:

Possessives like můj are not always obligatory when it is clear whose thing it is from context (especially with close family: bratr, sestra, máma, táta…).
Using Můj bratr makes the possession explicit and is very natural when you introduce or specify who you are talking about.

So both are possible; Můj bratr just stresses that it is your brother.

Can u počítače go earlier in the sentence, like Můj bratr u počítače často rychle píše úkol?

Yes, this is also grammatical:

Můj bratr u počítače často rychle píše úkol.

It slightly shifts the feel:

Original: Můj bratr často rychle píše úkol u počítače.
→ flows as: who – how often & how – what – where.
Variant: Můj bratr u počítače často rychle píše úkol.
→ brings place (u počítače) closer to the subject, starting with where he usually is.

Both are acceptable. For learners, the more typical pattern is:

Subject – (adverbs) – Verb – Object – Place
Můj bratr často rychle píše úkol u počítače.