Learn Hardcore Croatian: Ljudi polako ulaze u tramvaj. - People are slowly getting into the tram.

Ljudi – people (plural of čovjek = person, man).
polako – slowly. It’s an adverb.
ulaze – they enter / they are entering. 3rd person plural present tense of ulaziti (to enter, to go in).
u – in / into / to (here: into).
tramvaj – tram / streetcar.

So a very literal gloss would be: People slowly enter into tram.
In natural English: People are slowly getting on the tram.

Why is it Ljudi, not ljude?

This is about grammatical case.

Ljudi is nominative plural – used for the subject of the sentence (the “doer” of the action).
ljude is accusative plural – used mainly for direct objects.

In the sentence:

Ljudi = People (subject) – they are doing the action.
ulaze = are entering (verb).
u tramvaj = into the tram (prepositional phrase showing direction).

Because people are the subject (the ones who enter), Croatian uses Ljudi (nominative), not ljude (accusative).

What kind of word is polako, and can it mean anything besides “slowly”?

Polako is an adverb. Its basic meaning is slowly.

In sentences like this, it simply modifies the verb:

Ljudi polako ulaze u tramvaj.
→ People are slowly entering the tram.

However, polako is very common in spoken Croatian with additional shades:

as a calming word: Polako. → Take it easy. / No rush.
as a mild warning or request: Polako, polako! → Easy, easy! / Slow down!

But in your sentence, it has the straightforward adverb meaning: slowly.

Can polako go in another position in the sentence? Does that change the meaning?

Yes, Croatian word order is flexible, and polako can move:

Ljudi polako ulaze u tramvaj.
Ljudi ulaze polako u tramvaj.
Polako ljudi ulaze u tramvaj.

All are grammatically correct and still mean roughly: People are slowly entering the tram.

Subtle differences in emphasis:

Ljudi polako ulaze u tramvaj. – neutral; focuses on the action as “slow entering”.
Ljudi ulaze polako u tramvaj. – can sound slightly more like you’re adding “and they do it slowly” at the end.
Polako ljudi ulaze u tramvaj. – starts with polako, so it highlights slowness or could sound a bit like a comment: “Slowly, people start entering the tram.”

But in everyday speech, these differences are minor; all are acceptable.

What is the verb ulaze exactly? What is its infinitive form?

Ulaze is:

3rd person plural (they)
present tense
of the verb ulaziti.

So:

Infinitive: ulaziti – to enter (repeatedly/in general), to go in
oni ulaze – they enter / they are entering

Conjugation (present tense, briefly):

ja ulazim – I enter
ti ulaziš – you enter (sg.)
on/ona/ono ulazi – he/she/it enters
mi ulazimo – we enter
vi ulazite – you enter (pl./formal)
oni/one/ona ulaze – they enter

In this sentence, ulaze refers to people currently entering, which in English you often translate as are entering / are getting on.

Why is it ulaze and not a form of ući? What’s the difference between ulaziti and ući?

Croatian (like other Slavic languages) has aspect: imperfective vs perfective.

ulaziti – imperfective: focuses on the process, repeated or ongoing action
- e.g. Ljudi polako ulaze u tramvaj.
  → People are slowly entering the tram. (we see the ongoing action)
ući – perfective: focuses on the completed action, the result
- e.g. Ljudi su ušli u tramvaj.
  → People entered the tram. / People have gone into the tram. (they are already in)

In your sentence, we’re observing the action as it is happening, so the imperfective ulaziti → ulaze is used.

Why do we need u before tramvaj? Could we ever say Ljudi polako ulaze tramvaj?

You must use the preposition u here.

ulaziti (u nešto) – to enter (into something)
The thing you’re entering is normally introduced by u:
- ulaziti u kuću – enter the house
- ulaziti u autobus – get on the bus
- ulaziti u tramvaj – get on the tram

Ljudi polako ulaze tramvaj is incorrect. The verb ulaziti needs the preposition u (or iz when going out: iz tramvaja).

What case is tramvaj in after u, and why does it look the same as the basic form?

After u (meaning into, to with movement), Croatian normally uses the accusative case.

u + accusative → direction / movement into something
- u tramvaj – into the tram
- u kuću – into the house
- u školu – to school

Here, tramvaj is in the accusative singular.

For many masculine nouns ending in a consonant (like tramvaj), the nominative and accusative singular forms are identical:

Nominative sg.: tramvaj – subject
Accusative sg.: tramvaj – object/direction

You know it’s accusative here because of the preposition u + the meaning of motion (into).

What is the difference between u tramvaj and u tramvaju?

This is a classic case + preposition difference:

u + accusative (u tramvaj) → into the tram / onto the tram
- Shows movement towards/into something.
- Ljudi ulaze u tramvaj.
  → People are entering the tram.
u + locative (u tramvaju) → in the tram / on the tram (location)
- Shows where something or someone is.
- Ljudi sjede u tramvaju.
  → People are sitting in the tram.

So, u tramvaj = direction, u tramvaju = location.

How do I know if this means “People are slowly getting on the tram” or “People slowly get on the tram (habitually)”?

Croatian present tense covers both:

ongoing action (English present continuous)
general/habitual action (English simple present)

So Ljudi polako ulaze u tramvaj can mean:

People are slowly getting on the tram (right now).
People (in general) slowly get on the tram. (e.g. describing a typical situation)

The difference is understood from context, not from the verb form.
If the context is “What’s happening at this moment?”, English would use are getting on; if it’s about routine or habits, English would use get on.

There is no word for “the” or “a” here. How do I know if it’s “the tram” or “a tram”?

Croatian has no articles (no “a/an/the”). The noun tramvaj is just tram; definiteness or indefiniteness is understood from context, not from a special word.

Ljudi polako ulaze u tramvaj.
Depending on context, English can translate this as:
- People are slowly getting on *a tram.*
- People are slowly getting on *the tram.*

If you really need to emphasize one specific tram, you can clarify with extra words:

Ljudi polako ulaze u onaj tramvaj. – People are slowly getting on that tram.
Ti ljudi polako ulaze u tramvaj. – Those people are slowly getting on the tram.

But in many cases, simple tramvaj is enough, and English chooses the or a based on what sounds natural.

Could you say na tramvaj instead of u tramvaj?

For public transport like buses and trams, Croatian normally uses u (“into”):

u tramvaj – onto the tram
u autobus – onto the bus

Using na tramvaj in this context would sound wrong or very unusual.

Na is used more for:

surfaces: na stol – onto the table
some forms of transport that you are literally on top of (e.g. a bike, a horse):
- na bicikl – onto the bike
- na konja – onto the horse

So: Ljudi ulaze u tramvaj, not na tramvaj.

Is tramvaj masculine, feminine, or neuter? How would it change in plural?

Tramvaj is a masculine noun.

Basic forms:

Singular:
- Nominative: tramvaj – tram (as subject)
- Accusative: tramvaj – tram (as object/direction)
Plural:
- Nominative: tramvaji – trams
- Accusative: tramvaje – trams (object/direction)

Example with plural:

Ljudi polako ulaze u tramvaje.
→ People are slowly getting on the trams. (several different trams)

Could I replace Ljudi with another word like osobe or čovjek?

You can, but it changes the nuance:

Ljudi polako ulaze u tramvaj.
– People are slowly entering the tram.
– Neutral, most common.
Osobe polako ulaze u tramvaj.
– Persons/individuals are slowly entering the tram.
– Sounds more formal/official, like in regulations, announcements, or legal language.
Čovjek polako ulazi u tramvaj.
– A man/person is slowly entering the tram.
– Singular form, and čovjek usually suggests a (male) person specifically.

For a general, natural sentence like yours, Ljudi is the normal choice.