Learn Hardcore Croatian: Idemo autobusom do velikog jezera u dolini. - We are going by bus to a large lake in the valley.

idemo = we go / we are going
- idem – I go
- ideš – you go
- ide – he/she/it goes
- idemo – we go
- idete – you (pl) go
- idu – they go

So Idemo autobusom… already clearly means We are going by bus….
You can say Mi idemo autobusom… for emphasis (like stressing we, not someone else), but it’s not required.

Does idemo mean “we go” or “we are going”?

It can mean both. Croatian has only one present tense form here, and it covers:

English present simple:
- Svaki dan idemo autobusom. – We go by bus every day.
English present continuous:
- Sada idemo autobusom. – We are going by bus now.

Context (time expressions like sada = now, svaki dan = every day, sutra = tomorrow) tells you which English tense is the best translation. Croatian does not need a special -ing form.

Why is it autobusom and not autobus? What is the -om ending?

Autobusom is the instrumental singular of autobus (bus).

The instrumental case is used for means of transport / instrument:
- Idemo autobusom. – We go by bus.
- Idem vlakom. – I go by train.
- Idemo autom. – We go by car.
- Putujemo brodom. – We travel by boat.

For most masculine and neuter nouns, the instrumental singular ends in -om:

autobus → autobusom
vlak → vlakom
grad → gradom

So autobusom literally means “with a bus / by bus”.

Can I say Idemo s autobusom to mean “We are going by bus”?

No, that would be strange in Croatian.

s / sa
- instrumental usually means “with (a person/companion)”:
  - Idem s prijateljem. – I’m going with a friend.
  - Idem s mamom. – I’m going with (my) mom.

If you say Idemo s autobusom, it sounds like “We’re going together with the bus” (as if the bus is a companion walking next to you).

For transport, you normally do not use s/sa. You just use the bare instrumental:

Idemo autobusom. – We are going by bus. ✔
Idemo s autobusom. – grammatically possible, but semantically odd in this context ✘

Why do we use do before velikog jezera? Could we use u or na instead?

do takes the genitive case and usually means “to / up to / as far as” some boundary or point:

Idemo do velikog jezera. – We’re going (as far as) the big lake.

Rough comparisons:

do
- genitive: focus on reaching a point / boundary
  - do rijeke – to the river
  - do grada – to the town (up to it)
u
- accusative: into an enclosed space
  - Idemo u grad. – We’re going to / into the town.
  - Idemo u kuću. – We’re going into the house.
na
- accusative: onto / to a surface, island, event, etc.
  - Idemo na jezero. – We’re going to the lake (often more like “to the lake area / to spend time there”).
  - Idemo na otok. – We’re going to the island.
  - Idemo na koncert. – We’re going to the concert.

In Idemo autobusom do velikog jezera, the idea is reaching the lake as a destination point, so do + genitive is natural.

Why is it velikog jezera and not veliko jezero?

Because do requires the genitive case, not the basic nominative form.

Nominative (dictionary form):
- veliko jezero – a/the big lake (subject or basic mention)
Genitive (after do):
- do velikog jezera – to the big lake

Both the adjective and the noun must be in the same case and agree in gender and number:

veliko jezero – nominative singular, neuter
velikog jezera – genitive singular, neuter

So:

Vidim veliko jezero. – I see a big lake. (accusative = same form as nominative for neuter)
Idem do velikog jezera. – I’m going to the big lake. (genitive after do)

Why does jezero change to jezera? Isn’t -a usually plural?

Here jezera is not plural; it’s genitive singular.

The noun jezero (lake) is neuter. Many neuter nouns ending in -o form the genitive singular by changing -o → -a:

jezero → jezera (one lake, genitive singular)
selo → sela (of the village)
more (sea) → mora (of the sea)

This can be confusing because jezera is also the nominative plural (lakes). You tell them apart by context and other words:

mnoga jezera – many lakes (nominative plural; adjective mnoga is plural)
do velikog jezera – to the big lake (genitive singular; velikog is singular genitive)

Why is it u dolini and not u dolinu, even though we are going somewhere?

Because in this sentence the movement is to the lake, and the valley is just the location of the lake.

u dolini – in the valley (locative case, static location)
u dolinu – into the valley (accusative, direction/motion into)

The structure is:

Idemo autobusom – We are going by bus
do velikog jezera – to the big lake
u dolini – which (the lake) is in the valley

So we are not saying “we’re going into the valley”; we’re saying “we’re going to the lake, which is (located) in the valley”. Hence u dolini (locative).

In general, when does u take the locative and when the accusative?

Very broadly:

u
- locative → Where? (location, no movement)
  - Jezero je u dolini. – The lake is in the valley.
  - Živim u gradu. – I live in the city.
  - Sjedim u sobi. – I’m sitting in the room.
u
- accusative → Where to? (destination, movement into)
  - Idem u dolinu. – I’m going into the valley.
  - Idemo u grad. – We’re going to/into the city.
  - Uđi u sobu. – Go into the room.

In u dolini, dolini is locative: it answers Where is the lake? – In the valley.
If you change it to u dolinu, you change the meaning to “into the valley”.

Croatian has no “a/the”. How do we know if velikog jezera means “the big lake” or “a big lake”?

Croatian doesn’t have articles (a, an, the), so velikog jezera by itself could be translated as either of the big lake or of a big lake, depending on context.

In practice:

If speakers have a specific, known lake in mind (maybe there is one famous lake in that valley), English will use the:
- Idemo autobusom do velikog jezera u dolini. → We’re going by bus to the big lake in the valley.
If it’s any big lake, and not known to the listener, English would use a:
- “We’re going to a big lake in the valley.”

Croatian leaves this to context, not to grammar. The sentence itself doesn’t force a or the; the translator has to choose.

Can we move autobusom, do velikog jezera, and u dolini to other positions in the sentence?

Yes. Croatian word order is fairly flexible, especially with adverbials (by bus, to the lake, in the valley). Some natural variants:

Autobusom idemo do velikog jezera u dolini.
– Emphasis a bit more on by bus (put first).
Idemo do velikog jezera u dolini autobusom.
– Neutral or light final emphasis on by bus.
Do velikog jezera u dolini idemo autobusom.
– Emphasis on the destination.

What usually stays together:

do + velikog jezera (don’t split do far from its noun)
u + dolini (keep the preposition with its noun)

So you can shuffle these phrases as blocks, mainly to change emphasis or style, but not split the prepositions from their noun phrases.

Could we use another verb instead of idemo here, like vozimo se or putujemo?

Yes, but the nuance changes slightly:

ići (here: idemo) – very general to go, by any means: on foot, by car, by bus, etc.
- Idemo autobusom do velikog jezera. – We’re going by bus to the big lake.
voziti se – to ride / travel in a vehicle (focus on being a passenger).
- Vozimo se autobusom do velikog jezera. – We’re riding the bus to the big lake.
putovati – to travel, usually suggests a longer trip or journey.
- Putujemo autobusom do velikog jezera. – We’re travelling by bus to the big lake.

All are grammatically fine; idemo is the most neutral and common way to say it.