Learn Hardcore Czech: Otevři prosím okno, oběd je hotový a je tu horko. - Please open the window, lunch is ready and it is hot in here.

otevřít = infinitive (dictionary form) “to open”
Imperative (ty-form): otevřít → otevři (drop -t, add -i)
You use this form to tell one person you know well (friend, family, classmate) to do something.

If you said otevřít, that would just be “to open”, not a command.
Otevírat is the imperfective verb (“to be opening / to open repeatedly”), and its imperative would be otevírej, which would sound more like “keep opening” / “keep doing it”, or can sound more drawn-out or nagging in this context. For a one-time, simple request, the perfective otevři is standard.

For talking to more than one person or being formally polite, you’d use the vy-form: Otevřete (prosím) okno.

Why is prosím in the middle (Otevři prosím okno)? Can I move it?

Yes, prosím (“please”) is flexible in position. All of these are natural, with small differences in feel:

Prosím, otevři okno. – “Please, open the window.” (fronted, a bit more formal or emphatic)
Otevři prosím okno. – very common, smoothly polite
Otevři okno, prosím. – also common; “please” comes as a softener at the end

All three are polite in everyday speech. The middle position (Otevři prosím okno) and end position (Otevři okno, prosím) are probably the most typical in casual conversation.

Why is it okno? What case is that?

Okno (window) is in the accusative singular as the direct object of the verb otevřít (“to open [something]”).

Nominative singular: okno (subject)
Accusative singular: okno (object)

For neuter nouns in -o, the nominative and accusative forms are the same, so it looks identical, but grammatically it’s accusative here.

You could also say:

Otevři to okno. – “Open that window.” (to = “that”, also accusative)

Why don’t we say Ty otevři prosím okno? Where is the subject “you”?

In Czech, subject pronouns are usually dropped when the person is clear from the verb ending.

Otevři already marks 2nd person singular (“you, one person you speak to informally”), so ty is understood.

You would only add Ty for emphasis or contrast, for example:

Ty otevři okno, ne já. – You open the window, not me.

In a neutral request, Otevři prosím okno without ty is the natural form.

Why is it oběd je hotový and not something like oběd je horký or oběd je hotov?

hotový = “ready, finished, done”
horký = “hot” (high temperature)
hotov = shorter, more formal/literary form of hotový

So:

Oběd je hotový. – “Lunch is ready (to be eaten).”
Oběd je horký. – “Lunch is hot (temperature).”
Oběd je hotov. – also “Lunch is ready”, but sounds a bit formal, bookish, or old‑fashioned in everyday speech.

In a normal family / casual context, Oběd je hotový is the most natural way to say “Lunch is ready.”

What does je tu horko literally mean, and how is it different from just je horko or je tady horko?

je horko – “it is hot” (general statement about the weather or temperature)
je tu horko – “it is hot here (in this place/room)”
je tady horko – also “it is hot here”, very similar to tu

tu and tady both mean “here”:

tu – a bit shorter, slightly more neutral/everyday
tady – very common too, often a bit more emphatic or concrete (“right here”)

In this context (je tu horko), you’re stressing that it’s hot here in the room, which supports the request to open the window.
You could also say Je tady horko, which is equally natural.

Why is there a comma after okno but no comma before a?

The sentence has three clauses:

Otevři prosím okno – imperative (“Open the window, please”)
oběd je hotový – “lunch is ready”
(a) je tu horko – “and it’s hot here”

Czech punctuation rules:

Separate independent clauses with a comma:
→ Otevři prosím okno, oběd je hotový …
When two clauses are joined by a (“and”) in a simple way, you normally don’t put a comma before a:
→ … oběd je hotový a je tu horko.

That’s why there is a comma after okno, but none before a.

How polite is Otevři prosím okno, …? Is it too direct?

For someone you tutkáš (use ty with – friends, family, classmates, close colleagues), this is:

polite and completely normal in everyday speech
softened by prosím, so it doesn’t sound like a rude order

More or less polite variants (informal):

Softer, more tentative:
- Otevřel bys prosím okno? – “Would you open the window, please?”
- Mohl bys prosím otevřít okno? – “Could you please open the window?”
More direct, less polite:
- Otevři okno. – “Open the window.” (no prosím, can sound like a command)

For formal vy:

Otevřete, prosím, okno. – polite/formal
Even softer: Mohl byste / Mohla byste prosím otevřít okno?

Can I change the word order, like Prosím, otevři okno, oběd je hotový a je tu horko or Otevři okno prosím?

Yes, Czech word order is fairly flexible, and these options are all acceptable, with small stylistic differences:

Prosím, otevři okno, oběd je hotový a je tu horko.
– Slightly more formal or “announcing” style; prosím sets the tone right at the start.
Otevři okno prosím, oběd je hotový a je tu horko.
– Also fine; prosím at the end of the phrase softens the request.
Otevři prosím okno, oběd je hotový a je tu horko.
– Very natural, smooth rhythm, probably the most typical.

The main things that stay the same:

Otevři should come near the start of the request clause.
okno stays close to otevři, since it’s the object.
prosím can go before, between, or after otevři/okno without changing the meaning much.