Learn Hardcore Croatian: Znanstvenik radi u laboratoriju i proučava vodu. - The scientist male works in a laboratory and studies water.

Znanstvenik can mean “a scientist” or “the scientist” depending on context.
Laboratorij / laboratoriju can mean “a laboratory” or “the laboratory”.
Vodu can mean “water” in a general or specific sense (again, context decides).

So Croatian speakers rely on context, word order, and sometimes other words (like taj = that, ovaj = this) instead of articles.

Why is it znanstvenik and not znanstvenika?

Znanstvenik is in the nominative singular case — the basic dictionary form used for the subject of the sentence.

Znanstvenik radi… → The scientist works…
If znanstvenik were not the subject, the form would change:
- Vidim znanstvenika. = I see the scientist. (accusative)
- Bez znanstvenika. = Without the scientist. (genitive)

Here, znanstvenik is the one doing the action, so nominative is required.

What case is laboratoriju, and why is it used after u?

Laboratoriju is in the locative singular case.

In Croatian, certain prepositions require specific cases. U (in, at, into) is one of them:

u + locative → location where something happens (static “in/at”)
- u laboratoriju = in the laboratory
- u kući = in the house
- u školi = at school / in school

So radi u laboratoriju literally means “(he) works in the laboratory”, with laboratoriju in locative because it follows u indicating location.

Why is it laboratoriju and not laboratorij?

Laboratorij is the nominative form (dictionary form):

Ovo je laboratorij. = This is a laboratory.

When you say “in the laboratory” with u, you usually need the locative case:

u laboratoriju = in the laboratory

So:

Nominative: laboratorij
Locative: (u) laboratoriju

The ending -u here is part of the locative singular ending for this type of masculine noun.

Why is it vodu and not voda?

Voda is the nominative singular (dictionary form):

Voda je hladna. = The water is cold.

In proučava vodu, vodu is the direct object of the verb proučava (studies), so you need the accusative singular:

Nominative: voda (subject)
Accusative: vodu (object)

So:

Voda teče. = The water is flowing. (subject → nominative)
On proučava vodu. = He studies water. (object → accusative)

What is the difference between radi and proučava?

Both are 3rd person singular present tense, but from different verbs:

raditi = to work, to do
- on radi = he works / he is working
proučavati = to study, to research, to examine (in depth)
- on proučava = he studies / he is studying (researches)

So in the sentence:

radi u laboratoriju → he works in a laboratory (his job)
proučava vodu → he studies/researches water specifically

How can radi mean both “works” and “is working”?

Croatian has only one present tense form for both the English simple present and the present continuous.

So radi can mean:

“he works” (general, habitual)
“he is working” (right now)

Context decides which is more natural:

On svaki dan radi u laboratoriju.
= He works in the laboratory every day. (habit)
Sada radi u laboratoriju.
= He is working in the laboratory now. (right now)

In Znanstvenik radi u laboratoriju i proučava vodu, radi could be understood either way, but often it’s read as a general description of his job.

Why is there no “he” (on) in the sentence?

Croatian is a “pro-drop” language: subject pronouns (like ja, ti, on, ona) are usually omitted if the verb ending already shows the person.

Radi u laboratoriju.
Literally: Works in (the) laboratory.
Understood: He/She works in the laboratory.

Here, the subject znanstvenik is already present, so adding on (he) is usually unnecessary:

Znanstvenik radi u laboratoriju. = The scientist works in the laboratory.
Not: Znanstvenik on radi… (that would be unnatural or emphatic in a strange way).

Can the word order be changed, for example: U laboratoriju znanstvenik radi i proučava vodu?

Yes. Croatian word order is more flexible than English because meaning is largely carried by endings (cases), not position.

All of these are grammatically correct, with slightly different emphasis:

Znanstvenik radi u laboratoriju i proučava vodu.
→ Neutral, default order.
U laboratoriju znanstvenik radi i proučava vodu.
→ Emphasis on where he works (In the lab, the scientist works and studies water).
Znanstvenik u laboratoriju radi i proučava vodu.
→ Slight focus on the lab as the place of his work and research.

The basic meaning stays the same; word order mainly changes what you highlight.

What is the difference between i and a as translations of “and”?

Both i and a can be translated as “and”, but they are used differently:

i = and (neutral addition, same direction)
- radi i proučava = works and studies (just two actions of the same subject)
a = and/but (contrasting, or “on the other hand”)
- On radi, a ona proučava.
  = He works, and she studies / but she studies.

In your sentence, i is correct because you are simply listing two actions of the same subject with no contrast:

Znanstvenik radi u laboratoriju i proučava vodu.
= The scientist works in the laboratory and studies water.

Is there a difference between proučavati and učiti for “to study”?

Yes, important difference:

učiti = to learn, to study (as a student)
- Učim hrvatski. = I’m learning/studying Croatian.
proučavati = to research, to study in depth, to examine scientifically
- Znanstvenik proučava vodu.
  = The scientist studies / researches water.

So a scientist (znanstvenik) usually proučava a topic in a research sense, not uči it like a beginner student.

What is the aspect difference between proučava and prouči?

Croatian verbs often come in aspect pairs:

proučavati – imperfective (ongoing, habitual, process)
- On proučava vodu. = He studies / is studying water.
proučiti – perfective (completed action, result)
- On će proučiti vodu. = He will study (and finish studying) the water.

In the present tense, you normally use the imperfective for ongoing or repeated actions:

Znanstvenik proučava vodu. → His current/repeated research activity.

You typically don’t say On prouči vodu in the present to describe regular activity; perfective present tends to have future-like or single-completion meaning.

How would you say “The female scientist works in the laboratory and studies water”?

Croatian marks gender on many nouns:

znanstvenik = male scientist
znanstvenica = female scientist

So you would say:

Znanstvenica radi u laboratoriju i proučava vodu.

The verbs radi and proučava stay the same; only the noun changes to a feminine form.

How would you say “Scientists work in the laboratory and study water” (plural)?

You need plural forms for the noun and verbs:

Znanstvenici rade u laboratoriju i proučavaju vodu.

Changes:

znanstvenik → znanstvenici (plural, nominative)
radi → rade (3rd person plural of raditi)
proučava → proučavaju (3rd person plural of proučavati)

Laboratoriju and vodu stay singular here, because you are talking about one lab and water in general.