Learn Hardcore Croatian: Nemoj upaliti svjetlo u sobi. - Don't turn on the light in the room.

You can form a negative imperative with ne + imperative form (e.g. Ne pij! – Don’t drink!), but with many verbs and in everyday speech, nemoj + infinitive is more common and sounds more natural, especially for softer or more conversational prohibitions.

So:

Upali svjetlo. – Turn on the light. (affirmative imperative)
Nemoj upaliti svjetlo. – Don’t turn on the light. (negative imperative, natural)
Ne upali svjetlo. – Grammatically possible, but sounds harsher or unusual in many contexts; speakers generally prefer Nemoj upaliti / Nemoj paliti.

How is the negative imperative in Croatian generally formed?

There are two main patterns:

nemoj / nemojte / nemojmo + infinitive
- 2nd sg: Nemoj upaliti svjetlo. – Don’t turn on the light.
- 2nd pl / polite: Nemojte upaliti svjetlo. – Don’t turn on the light.
- 1st pl (rare / formal): Nemojmo to raditi. – Let’s not do that.
ne + imperative form of the main verb
- Ne pij! – Don’t drink!
- Ne govori! – Don’t speak!

Both are correct, but:

With many verbs, especially in everyday speech, nemoj + infinitive is more neutral and more common.
ne + imperative can sound sharper or more commanding, depending on context and intonation.

Why is the verb upaliti used here, and what’s the difference between upaliti and paliti?

Croatian distinguishes aspect:

paliti – imperfective (ongoing / repeated action)
“to be turning on / to turn on repeatedly / to keep the light on”
upaliti – perfective (single, whole action)
“to turn on once / to switch on”

In Nemoj upaliti svjetlo u sobi, the speaker is forbidding a single act of turning the light on (this one time).

Compare:

Nemoj paliti svjetlo u sobi. – Don’t (be) turning the light on (in general / as a habit / repeatedly).
Nemoj upaliti svjetlo u sobi. – Don’t go and switch on the light (this time, as one complete action).

In everyday conversation, both can be used, but the perfective upaliti fits well for “Don’t do this (once now).”

Could I also say Nemoj paliti svjetlo u sobi? How does that differ from Nemoj upaliti svjetlo u sobi?

Yes, you can say both, and both are correct, but the nuance changes slightly:

Nemoj paliti svjetlo u sobi.
Focus on ongoing / repeated action:
– Don’t (be) turning on the light in the room.
– Don’t use the light in that room.
– Don’t habitually keep that light on.
Nemoj upaliti svjetlo u sobi.
Focus on one concrete act:
– Don’t (even) turn on the light in that room (now / this time).

In many practical situations, speakers won’t think about this difference very consciously, but it’s how aspect works in the background.

What case is svjetlo in here, and why doesn’t its form change?

Svjetlo is a neuter noun and here it is in the accusative singular, because it’s the direct object of the verb:

(Nemoj upaliti) što? – svjetlo (what? – the light) → accusative.

For neuter nouns ending in -o, the nominative singular and accusative singular have the same form:

Nominative: Svjetlo je jako. – The light is strong.
Accusative: Vidim svjetlo. – I see the light.

So svjetlo looks like the base form, but grammatically it’s accusative in your sentence.

What gender is svjetlo, and does that matter here?

Svjetlo is neuter.

This matters because any adjectives or pronouns that modify it must agree in gender, number, and case:

upaliti jako svjetlo – to turn on a strong light
- jako – neuter, accusative singular
upaliti ovo svjetlo – to turn on this light
- ovo – neuter, accusative singular

In the sentence Nemoj upaliti svjetlo u sobi, there’s no adjective directly modifying svjetlo, so the gender agreement is not visible, but it would become important if you added modifiers.

What case is u sobi, and what’s the difference between u sobi and u sobu?

U sobi uses:

u
- locative singular of soba (room) → u sobi.

With u, the case depends on meaning:

u
- locative → location (answer to where?)
  - u sobi – in the room
u
- accusative → direction / movement (answer to into where?)
  - u sobu – into the room

So:

Nemoj upaliti svjetlo u sobi. – Don’t turn on the light in the room (location).
Uđi u sobu. – Go into the room (movement).

Can I change the word order, for example say Nemoj u sobi upaliti svjetlo? Does that change the meaning?

Yes, Croatian word order is flexible. You can say:

Nemoj upaliti svjetlo u sobi. (neutral, very natural)
Nemoj u sobi upaliti svjetlo.
Nemoj svjetlo upaliti u sobi. (less usual, but possible in some contexts)

The basic meaning (“Don’t turn on the light in the room”) stays the same. Changes in word order mainly affect:

Focus / emphasis
- Nemoj u sobi upaliti svjetlo. can slightly highlight u sobi (in that room specifically, as opposed to somewhere else).
Naturalness
- The original order (Nemoj upaliti svjetlo u sobi) is the most neutral and typical.

If you’re unsure, keep the original ordering: Nemoj upaliti svjetlo u sobi.

How would I say this to more than one person, or politely to someone I don’t know well?

Use the plural / polite form nemojte:

Nemojte upaliti svjetlo u sobi. – Don’t turn on the light in the room.

This is used for:

addressing several people, or
addressing one person politely (formal you).

You could also choose a less direct form, for politeness:

Molim vas, nemojte upaliti svjetlo u sobi. – Please don’t turn on the light in the room.

Is there a difference between svjetlo and svijetlo, or is one of them wrong?

Yes, there is a difference:

svjetlo – light (the noun) → correct in this sentence.
svijetlo – an adjective meaning bright, light (in color), e.g.:
- svijetlo plava boja – light blue color
- svijetla soba – a bright room (note the adjective form svijetla, not svijetlo here).

So in Nemoj upaliti svjetlo u sobi, you must use svjetlo (the noun, “light”), not svijetlo.

There is no word for “the” in the sentence. How do we know it means “the light in the room” and not “a light in a room”?

Croatian has no articles (no the, no a/an). Definiteness is expressed mainly by:

Context (what has already been mentioned / is obvious),
Word order and stress (what’s known vs. new information),
Sometimes demonstratives (taj, ovaj, onaj – that, this) if we need to be very clear.

In a typical real context, everyone knows which room and which light you’re talking about (for example, “this room’s ceiling light”). So:

Nemoj upaliti svjetlo u sobi. naturally translates as
Don’t turn on the light in the room.

If you really wanted to stress “that specific light”, you could say:

Nemoj upaliti ono svjetlo u sobi. – Don’t turn on that light in the room.