Learn Hardcore Croatian: Oba prijatelja su večeras u parku.

Oba means “both” – it refers to two specific items from a known set, and it implies that the set is fully covered (both of them, not just some of them).

Oba prijatelja su večeras u parku.
= Both (of the) friends are in the park tonight.

Dva just means “two”, with no built‑in idea that this is the whole set:

Dva prijatelja su večeras u parku.
= Two friends are in the park tonight. (maybe there are more friends who are not)

So:

use oba when you mean both of the two known friends,
use dva when you are only stating the number two, without implying “all of them”.

Also note:

oba is used with masculine and neuter nouns,
the feminine form is obje (see another question below).

Why is it prijatelja and not prijatelji?

The base noun is:

prijatelj – friend (masculine)
prijatelji – friends (nominative plural)

But in oba prijatelja, the word prijatelja is in the genitive singular form, because numbers like dva / tri / četiri / oba / obje normally require genitive singular of the noun that follows.

So:

jedan prijatelj – one friend (nominative singular)
oba prijatelja – both (of) friend → both friends (genitive singular form)
pet prijatelja – five friends (here it’s genitive plural, but the form happens to look the same)

For many masculine nouns like prijatelj, the genitive singular and genitive plural look identical (prijatelja), which is confusing, but in oba prijatelja it is grammatically genitive singular, even though the meaning is “two people”.

Is prijatelja here grammatically singular or plural, and how does the verb agree with it?

Formally, prijatelja after oba is genitive singular.
However, the whole phrase oba prijatelja refers to two people, so it is treated as plural for verb agreement.

That’s why we say:

Oba prijatelja su večeras u parku.
su = “are” (3rd person plural)

Using singular je (“is”) here (Oba prijatelja je…) is considered wrong or very non‑standard in Croatian. So you should always use plural verb forms after oba prijatelja when it is the subject.

What case is parku in, and why does it have that ending?

Parku is in the locative singular case.

In Croatian, the preposition u (“in”) can take:

locative – for location (where something/someone is)
accusative – for direction/movement (where something/someone is going)

Compare:

Oba prijatelja su večeras u parku.
Both friends are in the park tonight.
→ u + locative (parku) = location, “in the park”.
Oba prijatelja idu u park.
Both friends are going to the park.
→ u + accusative (park) = movement towards, “to the park”.

So here, because they are located in the park, we use u parku (locative: parku).

Why is the verb su placed where it is? Could it move to another position?

Su is a clitic (an unstressed short word) and Croatian likes to place such words very early in the sentence, typically after the first stressed unit (the so‑called “second position” rule).

In Oba prijatelja su večeras u parku, the first stressed unit is oba prijatelja, so su naturally comes right after it.

You can change the word order for emphasis, but su must still stay very early:

Večeras su oba prijatelja u parku.
→ Emphasis on “tonight” (contrast with other times).
U parku su oba prijatelja večeras.
→ Emphasis on the location “in the park”.

You should not normally put su at the very end:
✗ Oba prijatelja večeras u parku su. – sounds wrong in standard Croatian.

What exactly does večeras mean, and how is it different from words like večer or noćas?

Večeras is an adverb meaning “this evening / tonight” (usually the evening period, not the deep night).

Oba prijatelja su večeras u parku.
= Both friends are in the park this evening / tonight.

Related words:

večer – a noun, “evening”
- ove večeri – this evening (literally “of this evening”)
noćas – “tonight / during this night” (more focused on night‑time, later than evening)

So:

večeras – this evening (adverb)
noćas – tonight / this night, often later at night
ove večeri – on this evening (more formal/literary)

How would the sentence change if the two friends were female?

For two female friends, both the numeral and the noun change:

Obje prijateljice su večeras u parku.
= Both (female) friends are in the park tonight.

Changes:

oba → obje (feminine form of “both”)
prijatelj (male friend) → prijateljica (female friend)
prijateljice is the form used after obje (formally genitive singular here, though it looks like plural as well).

The verb su stays plural, exactly as before.

Could we use oboje or obojica instead of oba here? What’s the difference?

You can use related forms, but they carry slightly different nuances and grammar:

oba / obje
- simplest, most neutral “both” before a noun
- oba prijatelja, obje prijateljice
obojica
- used for two male persons
- behaves like a noun: obojica prijatelja = “the two (male) friends”
- verb is plural:
  - Obojica prijatelja su večeras u parku.
oboje
- a collective numeral, often for mixed gender or things/people as a pair
- usually followed by a genitive plural:
  - Oboje prijatelja je večeras u parku.
- grammatically neuter singular, so often takes singular verb (je), though in speech plural sometimes appears.

For a learner, the simplest and safest form in this context is Oba prijatelja su večeras u parku.

Why is there no word for “the” in oba prijatelja? How do we know it means “both (of) the friends”?

Croatian has no articles like English “a / an / the”.
The meaning that in English is carried by “the” is expressed in Croatian by:

context (we already know which friends)
sometimes word order and emphasis
sometimes demonstratives like taj / ovaj (“that / this”) if you really need to be explicit.

In this sentence, oba prijatelja is naturally understood as “both (of the) friends”, because:

oba already implies a specific pair,
context normally tells us which friends we are talking about.

If you really wanted to mirror English “these two friends”, you could say for example:

Ova dva prijatelja su večeras u parku. – These two friends are in the park tonight.