Learn Hardcore Croatian: Da je danas ljeto, plivali bismo na plaži. - If it were summer today, we would be swimming at the beach.

da je here introduces an unreal/irrealis condition (similar to English “if only it were / if it were”).
ako je normally introduces a real or possible condition (“if it is/if it will be”), like:
- Ako je danas ljeto, plivat ćemo na plaži. – If it is summer today, we will swim at the beach. (a real possibility)

So:

Da je danas ljeto, plivali bismo… ≈ If it were summer today, we would be swimming… (imaginary)
Ako je danas ljeto, plivat ćemo… ≈ If it is summer today, we’ll swim… (real/unknown)

Why is the verb je (present) used in da je danas ljeto, even though the whole situation is unreal?

In this type of unreal condition in Croatian, the clause with da often uses the present tense of “biti” (to be):

da je danas ljeto – literally that it is summer today → understood as if it were summer today.

English uses a special “past” form (were), but Croatian does not mark irreality this way. Instead:

irreality is shown by the combination:
- da + present tense in the if-clause
- conditional (bismo plivali) in the main clause

So grammatically it looks “present + conditional,” but the meaning is unreal/imaginary.

Could we also say Da bi danas bilo ljeto, plivali bismo na plaži?

You might hear forms like da bi… bilo in speech, but:

For a straightforward unreal condition, Da je danas ljeto, plivali bismo… is more natural and standard.
Da bi danas bilo ljeto tends to sound heavier or stylistically marked, and more like “for it to be summer today…” (a kind of wish or requirement) than a simple if it were.

For normal “If it were X, we would Y” sentences, stick to:

Da je X, radili bismo Y.
- Da je sada mir, spavali bismo. – If there were peace now, we would sleep.

Why is it plivali bismo, not bismo plivali?

bismo is a clitic form of the verb biti used to make the conditional (“we would”). Croatian clitics normally stand in second position in the clause, after the first stressed word or phrase.

In Plivali bismo na plaži:

First stressed word: plivali
Clitic goes second: bismo
Rest of the sentence: na plaži

Starting a sentence with Bismo plivali… is not correct in standard Croatian, because a clitic cannot be the very first element of the clause.

Other correct options:

Mi bismo plivali na plaži. (first word mi, then clitic bismo)
Na plaži bismo plivali. (first phrase Na plaži, then bismo)

What exactly does bismo mean, and how is the conditional formed in Croatian?

bismo is the 1st person plural conditional of biti (we would).

The conditional is formed with:

The past active participle (l-participle) of the main verb
The conditional form of “biti” (bih, bi, bismo, biste, bi)

For plivati (to swim):

plivao bih – I would swim (male speaker)
plivala bih – I would swim (female speaker)
plivao bi / plivala bi – he/she would swim
plivali bismo – we would swim (group incl. at least one male or mixed)
plivale bismo – we (all female) would swim
plivali biste / plivale biste – you (pl.) would swim
plivali bi / plivale bi – they would swim

So plivali bismo = we would swim.

Why is the form plivali used, and not an infinitive like bismo plivati?

Croatian does not form the conditional with “would” + infinitive like English. Instead, it uses:

past active participle (l-participle) + bih/bi/bismo/biste/bi

So:

plivali bismo – literally we would-have-swum → understood simply as we would swim.

Using bismo plivati is incorrect. The infinitive plivati can appear after modal verbs (e.g. moramo plivati – we must swim), but not for the conditional construction.

How does gender agreement work in plivali bismo?

The participle plivali agrees with the gender and number of the subject:

If the subject group is:
- All male or mixed (at least one male): plivali bismo
- All female: plivale bismo

Examples:

Group of boys/men or mixed group:
Mi bismo plivali na plaži.
Group of only women:
Mi bismo plivale na plaži.

In writing, if gender is unknown or irrelevant for a mixed group, plivali is the default.

Why is it na plaži and not na plažu?

The preposition na can take:

Locative (answering where? – location)
Accusative (answering where to? – direction/motion)

In the sentence:

na plaži – locative singular of plaža (on/at the beach)
The question is where? → location, so na plaži is correct.

Compare:

Plivali bismo na plaži. – We would be swimming at/on the beach. (location)
Išli bismo na plažu. – We would go to the beach. (direction)

Could we say u plaži instead of na plaži?

No, u plaži is not natural Croatian.

u = in / inside
na = on / on top of / at (a surface or open area)

A plaža (beach) is conceptualized as an open surface/area, so you are on it, not in it:

na plaži – on/at the beach
u moru – in the sea
u vodi – in the water

You could combine them:

Plivali bismo u moru, na plaži. – We would be swimming in the sea, at the beach.

Why is it ljeto and not ljeti in this sentence?

ljeto is a noun meaning “summer”.
ljeti is an adverb meaning “in (the) summer / during summer (in general)”.

In Da je danas ljeto, ljeto is the subject of the clause:

literally: if today were summer (i.e. if it were the season of summer today)

You cannot use ljeti there, because an adverb cannot be the subject:

✗ Da je danas ljeti – incorrect

But both can appear in different sentences:

Ljeti plivamo na plaži. – In summer (generally), we swim at the beach.
Sada je ljeto. – It is summer now.
Da je sada ljeto, plivali bismo na plaži. – If it were summer now, we would be swimming at the beach.

Is Da je danas ljeto, plivali bismo na plaži the only correct word order for the first part, or can we say Da je ljeto danas?

You can change the word order somewhat:

Da je danas ljeto, plivali bismo na plaži. – neutral, common.
Da je ljeto danas, plivali bismo na plaži. – also grammatically correct, but sounds a bit less natural; the focus slightly shifts to danas (“if it were summer today”).

Word order in Croatian is relatively flexible, but:

Time adverbs like danas are very commonly placed early in the clause.
The given order Da je danas ljeto is the most natural in everyday speech.

Could the sentence also be Plivali bismo na plaži da je danas ljeto, and what about the comma?

Yes, you can put the conditional clause at the end:

Plivali bismo na plaži da je danas ljeto.

Regarding the comma:

When the da-clause comes first, a comma is normally used:
- Da je danas ljeto, plivali bismo na plaži.
When the da-clause comes after the main clause and is closely connected in meaning, it’s usually written without a comma in modern usage:
- Plivali bismo na plaži da je danas ljeto.

So both variants are correct; it’s mostly a matter of word order preference and rhythm.

Is the subject “we” (mi) missing in Plivali bismo na plaži?

The subject “we” is not missing; it’s implied in the verb form.

bismo is only used for 1st person plural → “we would”.
Because Croatian verb forms carry person/number information, subject pronouns (ja, ti, mi, vi…) are often dropped when they are clear from context.

You can add it if you want to emphasize “we”:

Mi bismo plivali na plaži. – We would be swimming at the beach. (emphasis on “we”)

Does Da je danas ljeto sound natural in Croatian, or would people more likely say something else?

Da je danas ljeto, plivali bismo na plaži is natural and correct.

Other very common alternatives are:

Da je sada ljeto, plivali bismo na plaži. – If it were summer now…
Da je ljeto, plivali bismo na plaži. – If it were summer, we would be swimming at the beach. (no mention of “today/now”, context-dependent)

All of these are fine. The choice between danas and sada is mostly stylistic; both are frequent in this type of hypothetical sentence.