Learn Hardcore Croatian: Na predavanju o okolišu profesor govori o opasnosti plastike za našu zemlju i planet. - At the lecture about the environment the professor talks about the danger of plastic for our country and the planet.

You could technically hear u predavanju, but that would sound unusual and would suggest “inside the text/structure of the lecture” (very abstract), not simply “while attending the lecture”. For “at the lecture” as an event, na predavanju is the normal, idiomatic choice.

What case is predavanju, and why does it end in -ju?

Predavanju is in the locative singular case.

The base noun is predavanje (neuter, “lecture”).
Its locative singular form is predavanju.

The locative is required here because of the preposition na in the sense of “at (an event/place)”. Many neuter nouns ending in -anje / -enje (derived from verbs) have:

Nominative singular: predavanje
Locative singular: predavanju

A mini-pattern:

predavanje → na predavanju
stanovanje (living, residing) → u stanovanju
učenje (learning) → u učenju

So: na + locative = na predavanju.

Why is it o okolišu and o opasnosti, and what case do these nouns take after o?

The preposition o (“about”) is followed by the locative case.

In the sentence:

o okolišu – “about the environment” → okoliš (nom.) → okolišu (loc. sg.)
o opasnosti – “about the danger” → opasnost (nom.) → opasnosti (loc. sg.)

So the pattern is:
o + [noun in locative] = “about [noun]”

More examples:

govoriti o problemu – to talk about the problem
članak o zdravlju – an article about health
knjiga o povijesti – a book about history

That’s why you see okolišu and opasnosti, not okoliš / opasnost in their basic (nominative) forms.

What is the difference between okoliš and okolina? Could the sentence use okolina instead of okoliš?

Both okoliš and okolina relate to “environment”, but they’re not used in exactly the same way.

okoliš is the more technical or official word for “(the) environment” in the ecological, environmental-protection sense.
- zaštita okoliša – environmental protection
- ministarstvo okoliša – ministry of the environment
okolina is more like “surroundings / vicinity / area around something or someone”.
- moja okolina – my surroundings
- u gradskoj okolini – in the area around the city

In this sentence, because it is a lecture about the environment in an ecological context, o okolišu is the natural and correct choice.
You could say o životnoj okolini (“about the living environment”) in a more descriptive style, but o okolišu is the standard term.

Why is it opasnosti plastike, not opasnost plastika or opasnost plastika?

The phrase opasnosti plastike is actually made of two different cases:

opasnosti is locative singular, required by the preposition o → o opasnosti (“about the danger”)
plastike is genitive singular, depending on opasnost → “danger of plastic”

So structurally:

o
- opasnosti (locative) → “about the danger”
opasnost + genitive (plastike) → “danger of plastic”

This noun + genitive pattern is very common to express “X of Y”:

opasnost požara – danger of fire
problem ovisnosti – problem of addiction
nedostatak vode – lack of water

Using opasnost plastika (nominative plural) or opasnost plastika (incorrect form) would break the grammar; you need plastike in the genitive to show “danger of plastic”, and opasnosti in the locative because of o.

Can you omit the second o and say profesor govori opasnosti plastike?

No — you cannot omit the second o in this sentence.

The verb govoriti (“to speak, to talk”) requires the preposition o when you say what you are talking about:
- govoriti o nečemu – to talk about something

So you must say:

profesor govori o opasnosti plastike

If you say profesor govori opasnosti plastike, it sounds ungrammatical, because govoriti without o normally takes either no object or a different structure (e.g. govoriti istinu – “to tell the truth”, where it behaves more like “say/tell”).

Notice that there are two independent phrases:

na predavanju o okolišu – “at the lecture about the environment”
govori o opasnosti plastike – “he talks about the danger of plastic”

Each o belongs to a different part:

predavanje o okolišu
govoriti o opasnosti

You could join them if you changed the structure, e.g.
Na predavanju profesor govori o okolišu i opasnosti plastike.
Here one o governs okolišu i opasnosti plastike together. But in your original sentence each o is part of a different phrase.

What is the difference between govori (from govoriti) and priča (from pričati)? Could we say profesor priča o opasnosti plastike?

Both govoriti and pričati can be translated as “to talk”, but they have different tones:

govoriti is more neutral/formal:
- profesor govori – the professor is speaking (lecture-style, informational)
- govoriti istinu – to tell the truth
- govoriti o politici – to speak about politics
pričati is more informal, story-like, “to tell, to narrate, to chat”:
- pričati priču – to tell a story
- pričati o odmoru – to chat about the holidays
- pričati viceve – to tell jokes

In your sentence, profesor govori o opasnosti plastike sounds academic and appropriate for a lecture.

You could say profesor priča o opasnosti plastike, but it would feel more like:

“the professor is chatting/talking (in a more narrative, informal way) about the danger of plastic” So it changes the tone from formal lecture-style to more story-like / casual speaking.

Why is it za našu zemlju i planet, and what case is našu zemlju and planet in?

The preposition za (“for”) is followed by the accusative case when it means “for (the benefit/harm of)”.

In the sentence:

našu zemlju – “our country / our Earth” → zemlja (nom.) → zemlju (acc. sg. fem.)
planet – stays planet in accusative singular (it’s a masculine noun; nom. sg. = acc. sg. when it’s inanimate)

So:

za + accusative → za našu zemlju i planet

Some parallel examples:

za djecu – for the children
za našu budućnost – for our future
za cijeli svijet – for the whole world

That’s why you see zemlju (not zemlja) and našu in its accusative feminine form (see next questions).

Why do we only say našu once in za našu zemlju i planet? Would za našu zemlju i naš planet also be correct?

Both are grammatically correct:

za našu zemlju i planet
za našu zemlju i naš planet

In Croatian (as in English: “our country and planet”), an adjective can be understood as applying to both nouns in a coordinated pair, so you don’t have to repeat it.

However:

za našu zemlju i planet sounds smoother and is very natural in speech.
za našu zemlju i naš planet puts a bit more emphasis on planet as also being “ours”.

Note that if you do repeat it, the forms of naš must agree with each noun:

našu zemlju – feminine accusative singular
naš planet – masculine accusative singular (same as nominative for inanimate)

Why is it našu zemlju, not naša zemlja?

This is about case agreement between the noun and the possessive adjective naš.

The base forms are:

zemlja – nominative singular feminine
naša – nominative singular feminine of “our”

But in the sentence, zemlja is the object of za (“for”), so it must be in the accusative:

zemlja → zemlju (accusative singular feminine)

The possessive adjective must match that:

naša (nom. fem. sg.) → našu (acc. fem. sg.)

So:

nominative: naša zemlja – our country / our Earth (as subject)
accusative: za našu zemlju – for our country / our Earth (as object)

The same type of change happens with other feminine nouns:

moja knjiga (nom.) → vidim moju knjigu (acc.)
tvoja sestra (nom.) → za tvoju sestru (acc.)

Does zemlja here mean “country” or “planet Earth”? Why isn’t it capitalized?

The noun zemlja has several related meanings:

zemlja – country, land, state
zemlja – soil, ground, earth
Zemlja (capitalized) – the planet Earth (proper name)

In za našu zemlju i planet, the most natural reading is:

našu zemlju – “our country / our land (where we live)”
planet – “the (whole) planet”

So the idea is “danger of plastic for our country and the planet”.

If the author wanted to emphasize the planet specifically as a proper name, they could write:

za našu Zemlju i planet – “for our Earth and the planet” (a bit odd, redundant), or
more likely: za naš planet Zemlju – for our planet Earth.

Because zemlju is not capitalized, it is not the proper name “Earth” here; it is just “our country / our land” in a general, common-noun sense.

How flexible is the word order? Could we say Profesor na predavanju o okolišu govori o opasnosti plastike…?

Croatian word order is relatively flexible, and your alternative is correct:

Original:

Na predavanju o okolišu profesor govori o opasnosti plastike za našu zemlju i planet.

Alternative:

Profesor na predavanju o okolišu govori o opasnosti plastike za našu zemlju i planet.

Both are grammatical. The difference is mostly about focus and style:

Starting with Na predavanju o okolišu emphasizes the setting:
“During the lecture on the environment, the professor talks about…”
Starting with Profesor emphasizes the subject:
“The professor, in the lecture on the environment, talks about…”

Croatian allows you to move elements like profesor, na predavanju o okolišu, o opasnosti plastike around, as long as:

you don’t break fixed pairs like govoriti o + locative
you keep prepositions with their nouns

For example, all of these are fine, with slightly different emphases:

Profesor govori na predavanju o okolišu o opasnosti plastike…
O opasnosti plastike profesor govori na predavanju o okolišu…

Can you break down which case each noun in the sentence is in, and why?

Sure, here is each noun phrase with its case and reason:

na predavanju
- predavanju – locative singular
- Because of preposition na (“at”) indicating location/event.
o okolišu
- okolišu – locative singular
- Required by o (“about”).
profesor
- profesor – nominative singular
- Subject of the verb govori.
o opasnosti
- opasnosti – locative singular
- Again required by o (“about”).
plastike
- plastike – genitive singular
- Dependent on opasnost: opasnost plastike = “danger of plastic”.
za našu zemlju
- zemlju – accusative singular
- Required by za (“for” + accusative).
(našu) zemlju
- našu – accusative singular feminine of naš, agreeing with zemlju.
(i) planet
- planet – accusative singular masculine (same form as nominative for inanimate nouns)
- Also governed by za (“for”) together with zemlju.

So the prepositions na, o, za are the main drivers of the cases here, plus genitive after opasnost.